Table of contents

Developments in the connected fields of optics, optoelectronics and photonics have had a profound effect on the emergence of modern technologies and their influence on our lives. In all of these fields, understanding and improving the basic underlying materials is of crucial importance for the development of systems and applications. The International Conference on Optical, Optoelectronic and Photonic Materials and Applications (ICOOPMA) has successfully married these fields and become a regular feature in the conference calendar. The 6th conference in the series, held at the University of Leeds from 27th July – 1st August, 2014, continued the ICOOPMA tradition and attracted 220 international delegates with a diverse range of disciplines and interests. The 59 papers in this Proceedings provide an excellent overview of the topics presented. The conference consisted of four thematic areas in the fields of inorganic semiconductors, carbon and polymeric materials, inorganic glasses and crystalline materials, and metamaterials and plasmonics where each theme area included research on basic materials through to device applications.

The conference began with a Workshop organised by Professor Dan Hewak (University of Southampton) with speakers covering Organic Optoelectronic Complexes (Dr Richard Curry, University of Surrey), Metamaterials (Dr Vassili Fedotov, University of Southampton), Graphene (Dr Monica Craciun, University of Exeter) and Amorphous Semiconductors (Dr Jiri Orava, University of Cambridge and Tohoku University). This provided an excellent overview of a representative range of the important topics that were discussed further at the conference. The conference included a banquet which successfully combined excellent food with a relaxing opportunity for the conference delegates to socialise and network. The pinnacle of the evening was the after dinner speech given by our distinguished guest, Professor Sir David Payne (University of Southampton), who gave a highly informative and humorous history of the development of photonics and the important role played by optical fibres, of which he was one of the key pioneers. Emerging scientific talent was also given a platform, with a particular feature of the conference being the Young Scientists Forum, organised by Dr Senthil Ganapathy (University of Southampton), consisting of a series of themed sessions providing up-and-coming researchers a opportunity to present and discuss their work.

Each technical theme of the conference was introduced with Plenary lectures delivered by leading international figures in their respective fields. Professor Jim Harris (Stanford University) discussed the development of epitaxially grown dilute-nitride semiconductors and the important role that they play in high efficiency solar cells. This theme was continued by Professor Wolfgang Stolz (Philipps University, Marburg) who described the use of novel III-V semiconductors for the development of lasers on silicon. Dr Jerry Meyer (Naval Research Laboratories) and Dr Kumar Patel (Pranalytica) discussed the important field of mid-infrared devices highlighting the significant developments that have been made in inter-band cascade and quantum cascade based devices, respectively and which have wide-ranging applications in sensing. Professor Neil Greenham (University of Cambridge) discussed solution-based semiconductors based on conjugated polymers and nanocrystals offering low cost routes to the wide-scale deployment of photonics. Professor Ortwin Hess (Imperial College) gave an overview of the physics and fascinating technological potential of negative refractive index materials. Professor Stephen Elliott (University of Cambridge) discussed the optoelectronic properties of phase change materials for memories. These areas were expanded upon in over 70 invited talks from international speakers highlighting recent developments in each of these areas. Further detailed discussions were presented in many parallel Oral and Poster sessions.

This Proceedings provides an exciting and wide-ranging discussion of the topics presented at ICOOPMA 2014. We are very grateful to the many people who helped with the organisation of the conference, with particular thanks to Alison Whiteley and her team who enabled the smooth running of the conference, Dr Senthil Ganapathy for his many and wide ranging contributions to the conference and finally Professor Safa Kasap for his wisdom, advice and strong support. The conference could not have happened without the commitment of the Local Organising Committee, who helped in many ways to assemble and run the conference, and for the International Programme, Advisory and Steering committees who guided the technical direction of the conference and assisted with the conference programme and proceedings. We are also extremely pleased to have received generous sponsorship from a large number of organisations and companies. Finally, we are also very grateful to Sarah Toms and the Editorial staff at the Institute of Physics, and the many contributors and reviewers for helping us to put-together this proceedings.

Stephen Sweeney, Guildford, UK Animesh Jha, Leeds, UK

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We present a novel process for integrating germanium with silicon-on-insulator (SOI) wafers. Germanium is implanted into SOI which is then oxidized, trapping the germanium between the two oxide layers (the grown oxide and the buried oxide). With careful control of the implantation and oxidation conditions this process creates a thin layer (current experiments indicate up to 20-30nm) of almost pure germanium. The layer can be used potentially for fabrication of integrated photo-detectors sensitive to infrared wavelengths, or may serve as a seed for further germanium growth. Results are presented from electron microscopy and Rutherford back-scattering analysis, as well as preliminary modelling using an analytical description of the process.

To induce an amorphous surface in a nano-crystalline silicon (nc-Si:H) thin film, the hydrogen dilution was reduced step-wise at fixed time intervals from 90 – 50% during the hotwire chemical vapour deposition process. This contribution reports on the structural properties of the resultant nc-Si:H thin film as a function of the deposition time. Raman spectroscopy, confirmed by high resolution transmission spectroscopy, indicates crystalline uniformity in the growth direction, accompanied by the progression of an amorphous surface layer as the deposition time is increased. The silicon- and oxygen bonding configurations were probed using infrared spectroscopy and electron energy loss spectroscopy. The growth mechanism is ascribed to the improved etching rate by atomic hydrogen in nano-crystalline silicon towards the film/substrate interface region. The optical properties were calculated by applying the effective medium approximation theory, where the existence of bulk and interfacial layers, as inferred from cross-sectional microscopy, were taken into account.

The impacts of interface roughness (IR) scattering on device performance of indirectly-pumped (IDP) terahertz quantum cascade lasers are studied. Three different active region designs with almost the same lasing frequency at threshold and comparable oscillator strength are experimentally investigated and the measurement data are analyzed and compared with numerical simulation. The simulation results show that all structures suffer from the detrimental effect of intersubband roughness scattering in terms of threshold current density, and probably operating temperature. The intrasubband IR scattering time could also to be a limiting factor in the IDP structures due to the employed high energetic barrier.

The paper presents the advance process of synthesis of CdTe/CdSe core/shell Quantum Dots (QDs) with emission wavelength from 570 to 610 nm. This synthesis was performed using modified Hot-Injection method. The CdTe/CdSe core-shell QDs have been characterized by the transmission electron microscopy (TEM) with the aim to control the QDs shape and the average size. The optical absorption and photoluminescence (PL) spectra are investigated in four samples obtained at different reaction times (5, 10, 15 and 20 s) of core growth after the CdSe passivation of the CdTe cores. Obtained results have shown that synthesized QDs have a good crystallinity, spherical shape and bright emission at 610 nm. The reaction time enlargement permits increasing the average size of CdTe/CdSe core-shell QDs, together with "red" shifting the PL wavelength and increasing the PL intensity. The advantages of synthesized CdTe/CdSe core/shell QDs are discussed.

We have investigated the photoluminescence (PL) properties of a (GaAs)₁₂/(AlAs)₁₂ type-II superlattice (SL) at 10 K from the viewpoint of the formation of electron-hole droplets (EHDs). In the type-II SL, the lowest-energy exciton consists of an X-electron and a Γ-heavy-hole confined in the AlAs and GaAs layers, respectively; namely, the optical transition is indirect in momentum and real space. The excitation-power density was widely changed from ∼1 mW/cm² to ∼1 kW/cm² for precisely observing changes of PL spectra. It was found that a broad PL band appears with a threshold-like nature in the energy region lower than the biexciton. This suggests the occurrence of the Mott transition. The prominent feature of the broad PL band is the fact that the spectral profile hardly depends on the excitation-power density, which is one of typical properties of EHDs. From the line-shape analysis of the PL spectra, we estimated the stability energy of the EHD to be ∼2.9 meV relative to the biexciton energy. The above results consistently demonstrate the formation of the EHD.

Second-harmonic generation (SHG) in layered TlInS₂ crystals was studied over the temperature range of 77-300 K using a confocal laser microscope system. As expected, the SHG signal was observed in the low temperature ferroelectric phase of the layered compound. In addition, the polarization properties of the SHG signals of TlInS₂ were investigated in the 80-180 K range. The results are in good agreement with those of the symmetric space group C³₂ in the ferroelectric phase.

Reversible photo-induced deformation of amorphous carbon nitride (a-CN_x) films was investigated. The films were deposited at 400 and 600 °C on a rectangular shaped ultrathin SiO₂ substrate by reactive radio frequency magnetron sputtering with graphite target and pure N₂ gas. The amount of deformation change was estimated from bending curvature of a-CN_x/SiO₂ bimorph structure. For the film deposited at 400 °C, it bent toward the film side under illumination. Photo-induced deformation of the film estimated from the bending angle was observed in the excitation energy of 1.77 to 3.35 eV. The maximum deformation was observed under illumination of 2.6 eV which corresponds with π-π* bond of carbon nitride. In contrast, the deformation was hardly observed in the films deposited at 600 ^oC.The difference in these two films was probably due to difference in sp² bonding and termination structures.

Herein, we report the use of high-efficiency crystalline-selenium-based (c-Se-based) thin-film heterojunction photodiodes in imaging devices. As a novel experiment, we use an image pickup tube with a photoelectric conversion layer consisting of n-gallium oxide (Ga₂O₃)/p-c-Se heterojunction photodiodes to obtain high-resolution images at a relatively low applied voltage. We reduce the thickness of the Ga₂O₃ layer to expand the depletion layer into the c-Se layer at a lower applied voltage. In addition, Sn-doping of the Ga₂O₃ layer effectively increases the carrier concentration, thereby allowing the photodiode to operate at lower voltage.

A Ga₂O₃/Ga₂O₃:Sn/CuIn_1-xGa_x(Se_1-yS_y)₂(CIGS) structure is proposed for use in visible light sensors. CIGS thin films have been investigated for high efficiency thin-film solar cells. The typical structure of CIGS solar cells consists of ZnO/CdS/CIGS. However, the quantum efficiency of this structure at short wavelengths is decreased due to optical absorption loss from the CdS layer. In this study, a Ga₂O₃ layer was adopted instead of a CdS layer. Ga₂O₃ has a wide band gap and high transmittance in the visible region. Furthermore, it was assumed that it could function as a hole-blocking layer to suppress hole injection from the anode. Additionally, a Ga₂O₃:Sn thin layer was laid on the CIGS layer to spread the depletion region to the CIGS layer, because the carrier density of the undoped Ga₂O₃ layer was much lower than that of the CIGS layer. In this structure, signal current multiplication and quantum efficiency greater than unity were observed at applied voltages over 3.5 V.

We study the linear optical responses of of ZnO, in which the degeneracy of the p-like states at the Γ point is lifted by the crystal field and spin-orbit interaction, and the n = 1 (A- and B-) excitons are optically allowed under the condition of E ⊥ c. The coupled system of the light and multi-component excitonsforms the three branches, i. e., lower, middle, and upper branches through the radiative coupling between A- and B-excitons. We theoretically reveal the ratio of the components of A- and B-excitons in the respective branches which is determined from diagonalization of self-consistent equation of the nonlocal induced-polarization and Maxwell electric field.

We present a study of 1.3-μm InAs/GaAs quantum dot lasers monolithically grown on Si substrates by molecular beam epitaxy. We focused on the optimization of III-V buffer layers epitaxy grown on Si substrates, which includes the nucleation layers and the dislocation filter layers. The effect of growth temperature of GaAs nucleation layer has been investigated. Additionally, InAlAs/GaAs and In GaAs/GaAs strained layer superlattices(SLSs) are compared as dislocation filter layers. Our results show the optimization of III-V buffer layers grown on Si is critical to achieve high performance quantum-dot lasers. An optimised 1.3-μm board-area laser has been demonstrated with a low threshold current density of 194 A/cm² and output power of 77 mW at room temperature.

We develop a theoretical formalism to calculate photoluminescence (PL) spectrum of weakly confined excitons incorporating the microscopic nonlocal optical response. The nonlocality is caused by the center-of-mass (c. m.) motion of exciton and becomes remarkable in nano-to-bulk crossover regime. The theory successfully explains the characteristics of recently observed peculiar PL spectra in high quality CuCl films [5], wherein the signals appear at the exciton states with the very large radiative corrections not only for the lowest level but also for the higher ones including non-dipole types of excitons.

The processes of light-induced defect creation in hydrogenated amorphous silicon consist of self-trapping of holes in a weak Si-Si bond adjacent to a Si-H bond, nonradiativerecombination of self-trapped holes with electrons, the Si-H bond switching towards the weak Si-Si bond, and hydrogen-hopping or -tunneling along the weak Si-Si bond. The Si-H bond switching and hydrogen movements are treated by Monte-Carlo computer simulation in a simple cubic lattice. From the result of <r²> vs t in which r and t designate diffusion distance of hydrogen and diffusion time, respectively, the density of light-induced defects is estimated in a good agreement with the observed density.

Hydrogenated amorphous silicon nitride (a-SiN_x:H) is used as anti-reflection coatings in commercial solar cells. A final firing step in the production of micro-crystalline silicon solar cells allows hydrogen effusion from the a-SiN_x:H into the solar cell, and contributes to bulk passivation of the grain boundaries. In this study a-SiN_x:H deposited in a hot-wire chemical vapour deposition (HWCVD) chamber with reduced gas flow rates and filament temperature compared to traditional deposition regimes, were annealed isochronally. The UV-visible reflection spectra of the annealed material were subjected to the Bruggeman Effective Medium Approximation (BEMA) treatment, in which a theoretical amorphous semiconductor was combined with particle inclusions due to the structural complexities of the material. The extraction of the optical functions and ensuing Wemple-DeDomenici analysis of the wavelength-dependent refractive index allowed for the correlation of the macroscopic optical properties with the changes in the local atomic bonding configuration, involving silicon, nitrogen and hydrogen.

We have investigated the photoluminescence (PL) properties in a CuBr microcavity with HfO₂/SiO₂ distributed Bragg reflectors at 10 K from the viewpoint of cavity-polariton condensation. From the excitation-power dependence of PL spectra detected at an in-plane wave vector of k_||=0, we found that the PL characteristics of the lower polariton branch markedly change with a threshold nature: a drastic increase (decrease) in the intensity (band width). In addition, the PL energy exhibits a large blueshift, ∼10 meV, around the threshold excitation power, reflecting strong polariton-polariton interactions. The blueshifted PL energy is far below the bottom energy of the cavity photon. In addition, the estimated density of photogenerated electron-hole pairs at the threshold excitation power is two orders lower than the Mott-transition density for the formation of electron-hole plasma. The above results consistently demonstrate the occurrence of the cavity-polariton condensation.

We present density of dangling bonds of silicon created in a-Si:H films by illumination of intense pulsed light at low temperature. The density of the photo-created dangling bonds decreases at room temperature with increasing time from illumination with a decay time estimated to be approximately 4.2 × 10⁶ s (48 days). The results are compared with the intensity and lifetime of defect PL in a-Si:H films measured at various time from the pulsed illumination.

In the experiments, ZnO and CuInSe₂ semiconductor powders were used (the latter produced by the high-temperature synthesis method). Microstructural properties of the powders were analyzed using X-Ray diffraction and SEM. The experimental ZnO/CuInSe₂ samples were prepared by the screen printing technique. The V–I measurements of the samples indicated the presence of a p-n junction in the ZnO/CuInSe2 contact zone. The samples were exposed to artificial solar radiation, during which an exponential decay of photo-emf was observed. It was shown that the starting conductive properties of the p-n junction restores in ∼ 15 min after the exposition. Laser ablation technique was applied to ZnO/CuInSe2 p-n junction with purpose to improve its performance and quality. After several attempts, significant changes in electrical properties of samples was observed. Improvenent of p-n junction can be achieved only at single attempt at certain amount of delivered energy. Futherablation attempt leads to degradation of p-n junction of samples.

In this work we examined the phase transitions in the ternary thallium chalcogenide TlGaSe₂ by studying the temperature dependence of the Raman spectra with the aid of confocal microscopy. The unpolarized Raman scattering spectra of TlGaSe₂ single crystals were measured over the temperature range 78- 300 K (which includes the range of the successive phase transitions) in the frequency region of 50 – 300 cm^-1. The Raman spectra exhibited 12 lines at 300 K, but the number of lines rose to 17 at 78 K. In the temperature interval between 107 K and 120 K, where the phase transitions take place, the temperature dependence of the phonon frequencies showed discontinuities for several of the Raman lines.

The present work demonstrates an analysis of electronic and optical characteristics of InAs/GaSbType II superlattice based photodetectors. The electronic characteristics are analyzed by developing a model of the Type II superlattice. The 8 band k.p method is implemented to deduce the wavefunctions. The effects of temperature on zero-bias resistance- area product (R₀A) are also included in the model. The newly proposed M-Structure design method is also implemented for our model. Electrical and optical properties of the material such as dark current density and absorption coefficient are calculated. At 50mV reverse bias, the dark current density is found equal to 1.5×10^-4 A/cm². These calculations are done based on the approximation based models of reflectivity. These results were used to demonstrate the variation of optical properties with applied bias voltage to be used as a novel optical switching technique in WDM based communication networks.

We have engineered both the optical and mechanical behaviour of a suspended line defect photonic crystal waveguide to demonstrate an improved sensor response. Utilizing thinner than the conventional photonic crystal membrane increases the mechanical sensitivity and the dynamic range of the sensor. The mechanical sensitivity is also increased by optimizing the membrane pad connected to the core photonic crystal waveguide. The pad optimization also ensures maximum pad flatness under uniform pressure. The overall sensitivity obtained is as high as 6% optical transmission change per Pa of pressure.

When the intersubband transitions of a doped quantum well are strongly driven by a coherent optical pump, the bare energy levels are split into dressed doublets, a phenomenon known as the ac Stark (or Autler-Townes) effect. In time domain this can be understood as Rabi oscillations of the confined electrons between two subbands. Here we show how, by employing asymmetric quantum wells, the selection rule preventing emission from an upper to a lower state of the same doublet can be lifted. The fluorescence spectrum of such strongly-driven system is then marked by an additional peak that would appear at the Rabi frequency, in the terahertz portion of the electromagnetic spectrum.

Low-cost semiconductor laser diode pump sources have made a dramatic impact in sectors such as advanced manufacturing. They are now disrupting other sectors, such as defence and security (D&S), where Thales UK is a manufacturer of sensor systems for application on land, sea, air and man portable. In this talk, we will first give an overview of the market trends and challenges in the D&S sector. Then we will illustrate how low cost pump diodes are enabling new directions in D&S sensors, by describing two diode pumped, solid- state laser products currently under development at Thales UK. The first is a new generation of Laser Target Designators (LTD) that are used to identify targets for the secure guiding of munitions. Current systems are bulky, expensive and require large battery packs to operate. The advent of low cost diode technology, merged with our novel solid-state laser design, has created a designator that will be the smallest, lowest cost, STANAG compatible laser designator on the market. The LTD delivers greater that 50mJ per pulse up to 20Hz, and has compact dimensions of 125×70×55mm. Secondly, we describe an ultra-compact, eye-safe, solid-state laser rangefinder (LRF) with reduced size, weight and power consumption compared to existing products. The LRF measures 100×55×34mm, weighs 200g, and can range to greater than 10km with a single laser shot and at a reprate of 1Hz. This also leverages off advances in laser pump diodes, but also utilises low cost, high reliability, packaging technology commonly found in the telecoms sector. As is common in the D&S sector, the products are designed to work in extreme environments, such as wide temperature range (-40 to +71°C) and high levels of shock and vibration. These disruptive products enable next- generation laser sensors such as rangefinders, target designators and active illuminated imagers.

Since its emergence a decade ago, amorphous silicon flat panel X-ray detector has established itself as a ubiquitous platform for an array of digital radiography modalities. The fundamental building block of a flat panel detector is called a pixel. In all current pixel architectures, sensing, storage, and readout are unanimously kept separate, inevitably compromising resolution by increasing pixel size. To address this issue, we hereby propose a "smart" pixel architecture where the aforementioned three components are combined in a single dual-gate photo thin-film transistor (TFT). In other words, the dual-gate photo TFT itself functions as a sensor, a storage capacitor, and a switch concurrently. Additionally, by harnessing the amplification effect of such a thin-film transistor, we for the first time created a single-transistor active pixel sensor. The proof-of-concept device had a W/L ratio of 250μm/20μm and was fabricated using a simple five-mask photolithography process, where a 130nm transparent ITO was used as the top photo gate, and a 200nm amorphous silicon as the absorbing channel layer. The preliminary results demonstrated that the photocurrent had been increased by four orders of magnitude due to light-induced threshold voltage shift in the sub-threshold region. The device sensitivity could be simply tuned by photo gate bias to specifically target low-level light detection. The dependence of threshold voltage on light illumination indicated that a dynamic range of at least 80dB could be achieved. The "smart" pixel technology holds tremendous promise for developing high-resolution and low-dose X-ray imaging and may potentially lower the cancer risk imposed by radiation, especially among paediatric patients.

We have investigated surface-modification effects on photoluminescence (PL) properties of the self-assemble monolayer of CdSe quantum dots from the viewpoint of the temperature dependence of PL properties. The band-edge PL band is strongly activated by the surface modification and is observed as the main PL band, contrary to the fact that the defect-related PL band is dominant in the as-grown sample. From the analysis of PL decay dynamics, it is demonstrated that the contribution of a bound exciton state to PL processes would suppress a trapping process to defects.

Temperature-dependent Eu³⁺ luminescence spectra in GaN(Mg):Eu can be assigned to, at least, two distinct Eu³⁺ centres, denoted by Eu0 and Eu1. The splitting energy levels of the ⁷F_J (J=1,2) multiplets for the Eu0 and Eu1 centres have been calculated using the equivalent operator Hamiltonian for C_3v crystal field with the addition of an odd parity distortion.

Organic materials display promise in numerous electronic applications, complimentary to traditional semi-conducting materials. Cyclolinopeptides show promise in light-emitting applications as an organic semiconductor. Photoluminescence measurements indicate charge transfer between the peptide and the metal, resulting in an increase in intensity of the emission from around the metal in the Cyclolinopeptide complex. Complementary X-ray absorption near-edge spectroscopy (XANES) shows a change in occupation of energy states in the peptide when complexed with the metal, indicating charge transfer, but peak positions show the peptide is not chemically changed by the metal. Combining X-ray emission and XANES provides element specific partial density of states, to estimate the element specific energy gap which is the proposed emission range for the peptide material. Organic light emitting diode devices have been fabricated, although no measurable emission has been seen as of yet. The devices have diode like current-voltage characteristics showing the peptide is semi-conducting with a threshold voltage of approximately 2.5 V.

Azobenzene containing compounds are among light polarization sensitive materials – the moieties may align relative to the electric field vector of light, leading to anisotropy and birefringence in the sample. Another phenomenon which can be observed in azo compounds under influence of light is macroscopic movement of the material. In this work photoinduced processes in low molecular weight organic glass – bis-azobenzene containing compound K-D-2 were experimentally studied. Birefringence was induced with linearly polarized laser light (473, 532 and 635 nm) and measured at 633 nm wavelength. Polarization holography with recording beam configuration +45°/-45° was used to induce mass motion. Dependence of the surface relief depth on the recording laser wavelength in the visible spectrum (375 – 671 nm) was obtained. Formation of the SRG was observed with all used wavelengths and high birefringence values were obtained. Certain correlation between the absorption of the wavelength and photoinduced mass transport and birefringence is yet to be confirmed.

A planar interdigitated sample substrate has been designed to support a thin-film sample of a polymer while the frequency-dependent dielectric properties of the thin film are measured. Trenches for the electrodes were etched into a SiO₂/Si wafer surface. Chromium was used as an adhesion layer prior to thermal evaporation of copper for the body of the electrode. The device was placed in a standard probe station and the dielectric character was recorded as a function of frequency with an impedance analyser. Devices with 20 to 70 fingers were measured and the results compared to analytical and finite element simulations. At 1 kHz, the total capacitance of a typical 20-finger device was 8 pF. The capacitive contribution of the thin film due to the fringing field in the polymer was about 2% of the total capacitance of the fabricated structures.

Organic Field Effect Transistors (OFET) possess wide applications in large area electronics owing to their attractive features like easy fabrication process, light weight, flexibility, cost effectiveness etc. But instability, high operational voltages and low carrier mobility act as inhibitors to commercialization of OFETs and various approaches were tried on a regular basis so as to make it viable. In this work, Poly 3-hexylthiophene-2,5diyl (P3HT) based OFETs with bottom-contact top-gate configuration using Poly vinyl alcohol (PVA) and Poly (methyl methacrylate) (PMMA) as gate dielectrics, aluminium and copper as source-drain electrodes are investigated. An effort is made to compare the effect of these dielectric materials and electrodes on the performance of OFET. Also, an attempt has been made to optimize the channel width of the device. These devices are characterised with mobility (μ), threshold voltage (V_T), on-off ratio (I_on/I_off) and their comparative analysis is reported.

The diffusion of singlet excitonsis known to occur through the Förster resonance energy transfer (FRET) mechanism and that of singlet and triplet excitonscan occur through the Dexter carrier transfer mechanism. It is shown here that if a material possesses the strong exciton-spin-orbit-photon interaction then triplet excitonscan also be transported /diffused through a mechanism like FRET. The theory is applicable to the diffusion of excitonsin optoelectronic devices like organic solar cells, organic light emitting devices and inorganic scintillators.

Ytterbium-doped waveguides are required for compact integrated lasers and Yb- doped Ta₂O₅ is a promising candidate material. The design, fabrication and spectroscopic characterisation of Yb:Ta₂O₅ rib waveguides are described. The peak absorption cross-section was measured to be 2.75×10^-20 cm² at 975 nm. The emission spectrum was found to have a fluorescence emission peak at a wavelength of 976 nm with a peak cross-section of 2.9×10^-20 cm² and a second broad fluorescence band spanning from 990 nm to 1090 nm. The excited- state life time was measured to be 260 μs.

Mid-IR imaging spectroscopy has the potential to offer an effective tool for early cancer diagnosis. Current development of bright super-continuum sources, narrow band acousto-optic tunable filters and fast cameras have made feasible a system that can be used for fast diagnosis of cancer in vivo at point of care. The performance of a proto system that has been developed under the Minerva project is described.

In conventional method, to identify location of the tumor intraperitoneally for extirpation of the gastric cancer, charcoal ink is injected around the primary tumor. However, in the time of laparoscopic operation, it is difficult to estimate specific site of primary tumor. In this study we developed a glass phosphors was realized with Yb³⁺, Nd³⁺ doped to Bi₂O₃-B₂O₃ based glasses, which have central emission wavelength of 1020 nm and 100 nm of FWHM. Using this glass phosphor, we developed a fluorescent clip and the laparoscopic fluorescent detection system for clip-derived near-infrared light. To evaluated clinical performance of a fluorescent clip and the laparoscopic detection system, we used resected stomach from the patients. Fluorescent clip was fixed on the gastric mucosa, and an excitation light (wavelength: 808nm) was irradiated from outside of stomach for detection of fluorescent through stomach wall. As a result, fluorescent emission from the clip was successfully detected. These results indicate that the glass fluorescent clip in combination with laparoscopic detection system is a very useful method to identify the exact location of the primary gastric cancer.

Ca 100, 200, 500, 1000 and 3000 at. ppm co-doped (Ce_0.01,La_0.3Gd_0.69)₂Si₂O₇ single crystals were grown by the μ-PD method. Luminescence and scintillation properties such as radioluminescence spectra, light yield and decay time were evaluated. Expected Ce³⁺ 4f5d emission have been observed in 350-430nm peaking at 360nm. Emission intensity took maximum at the Ca 100at.ppm co-doped sample and decreased by increasing the Ca concentration. The Ca 100at.ppm co-doped sample showed the highest light yield of around 20,000 photons/MeV. Scintillation decay time was accelerated with increasing Ca concentration. Scintillation decay time of the Ca 0, 100, 200, 1000 and 3000 at. ppm co-doped samples were 66.5ns(21%) 468ns(79%) and 44.0ns(22%) 430ns(78%), respectively.

Nonstoichiometric Lu₃Al_5+xO₁₂ (x= 0.05, 0.15, 0.35, 0, -0.05, -0.15, -0.35) crystals were grown by the μ-PD method. Luminescence and scintillation properties such as absorption, excitation and emission spectra, light yield and decay time were evaluated. Expected anti-site defect related host emission have been observed in 250-420nm. Emission intensity was increased by increasing the nonstochiometry. The x=-0.35 sample showed the highest light yield of around 12000 photons/MeV and slowest scintillation decay time of 1.96μs.

Ce:Gd₂Si₂O₇/SiO₂ eutectic was grown by the μ-PD method. The square-shape sample with a side of 5 mm and a length of 15 mm was obtained. Two phases of orthorhombic Gd₂Si₂O₇ and SiO₂ was observed. Rod-phase was SiO₂ and matrix phase was Gd₂Si₂O₇. Ce³⁺ 4f5d emission have been observed at 400nm. The sample showed light yield of around 16,000 photons/MeV. Scintillation decay time was 46.3ns(21%) 249ns(79%).

Laser induced cooling of solids or optical refrigeration is an area of optical science investigating interaction of light with condensed matter. This addresses a very important practical issue: design and construction all optical solid-state cryocoolers, which are compact devices, free from mechanical vibrations, moving parts, or fluids. They are based on reliable diode pump technology and in the most part free from electromagnetic interference in the cooled area. The optical cryocooler has a broad range of applications such as in the development of biomedical sensing, magnetometers for geophysical sensors and other sensors, satellite instrumentations where compactness and the lack of vibration are key parameters. The operation of these devices is based on anti-Stokes fluorescence also known as luminescence upconversion, in which light quanta in the red tail of the absorption spectrum are absorbed in a material from a pump laser and by adding thermal energy, blue-shifted photons are spontaneously emitted. Laser cooling of solids can be realized in rare-earth doped low phonon energy glasses and crystals as well as in direct band gap semiconductors. Both of these areas are very interesting and important and are discussed in this article.

X-ray induced luminescence (XL) properties of phosphor materials made of samarium doped barium sulfate have been investigated. The samples were prepared by sintering method heated at 900-1250 °C for 3 hours in air from the mixture of BaSO₄ and Sm₂O₃. The concentration of Sm were prepared from 0.01-6 at.%. In as-prepared sample, the Sm³⁺ was detected by photoluminescence (PL). The PL intensity is maximum about 2 at.% with Sm, and then starts decreasing. The PL intensity showed concentration quenching. The XL observed Sm²⁺ and Sm³⁺ ions. The XL was shown from the sample sintered up to 1200 °C. The XL intensity increased with Sm concentration up to 1 at.%. The intensity was almost constant larger than 1 at.% Sm. These concentration dependences is different since the X-ray energy absorbed to the host material at once, and the energy transferred to both Sm³⁺ and Sm²⁺ ions. Sm doped BaSO₄ is found a host for XL phosphor materials.

Since the light output of Zr⁴⁺ co-doped Ce:Gd₂SiO₅ scintillator improved compared with the Ce:Gd₂SiO₅ one, the light output and other scintillation properties of M⁴⁺/Ce³⁺ co-doped Gd₃Al₂ Ga₃O₁₂ (GAGG), where M = Zr, Hf, were investigated. (Gd_1-x, Ce_0.01, M_x)₃Ga₃Al₂O₁₂ (M=Zr, Hf, x = 0.001 and 0.0002) crystals were grown by the micro-pulling down (μ-PD) method. We found these samples had longer decay time constants and the light outputs of these co-doped samples were degraded compared with that of the conventional Ce:GAGG.

The conversion of ionic valence induced by X-ray irradiation can possibly be applied in X-ray imaging devices. Here, we report the X-ray irradiation time dependence of the valence change of Sm ions doped in a BaSO₄ matrix. The samples were prepared by sintering a mixture of BaSO₄ and Sm₂O₃ powder. The as-prepared sample consisted mainly of Sm³⁺. Sm²⁺ and Sm³⁺ were detected by using the photoluminescence (PL) spectral shapes. After X-ray irradiation (λ = 0.154 nm), the PL intensity of the Sm²⁺ increased proportionally to the X-ray irradiation time from 4 to 1000 s. The intensity began to saturate at more than 1000 s. The intensity of Sm³⁺ was constant regardless of the increasing Sm²⁺ intensity.

In this paper, using an inverse scattering approach, we describe how the selection of mode effective indices and thus phase velocities can be used to control group velocity in a waveguide. As such it is shown that differential group delay can be equalised or minimised over a wavelength of choice. A particular feature of the new designs is the development of rings and a peaked core which may split depending upon the number of guided modes. These designs show characteristics comparable with commercially available fibres but with refractive index profiles that differ from typical graded-index designs.

The exposure with band gap light of thermally evaporated As₄₀Sb₁₅Se₄₅ amorphous film of 800 nm thickness, were found to be accompanied by optical changes. The as-prepared and illuminated thin films were studied by X-ray diffraction, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy and Raman spectroscopy. The optical band gap was reduced due to photo induced effects along with the increase in disorder. These optical properties changes are due to the change of homopolar bond densities. The core level peak shifting in XPS spectra and Raman shift supports the optical changes happening in the film due to light exposure.

In the present study, NaYF₄-Yb³⁺/Er³⁺ having the composition NaYF₄-18%Yb³⁺/2%Er³⁺ and NaYF₄-20%Yb³⁺/2%Er³⁺ with and without the addition of PVP (polyvinyl pyrolidone) have been synthesised by a solution method using NaF, yttrium nitrate, ytterbium nitrate and erbium nitrate as precursors. Upconversion spectra of prepared nanomaterial under 980 nm laser excitation have been studied. The variation in upconversion spectra with new born calf serum and myoglobin has been studied. Myoglobin (Mb) may be helpful when used in conjunction with other cardiac markers for rapid determination of acute myocardial ischemia, especially in patients with a typical chest pain or nonspecific ECG changes. The variation of UC fluorescence with addition of Mb indicates the suitability of using NaYF₄ based UC nanoparticles in cardiac marker detection. The detailed study is currently under progress.

A high powered octagonal double clad ZBLAN (33 μm/330 μm, NA=0.13) glass fibre for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing and includes up-conversion phenomena. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at ZBLAN glass fibre air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. Simulation results show that the laser operation with 20 W of pump power at 0.98 μm wavelength can be achieved at 2.75 μm operating wavelength with Er³⁺ ion concentrations of 60,000 ppm.

Magnitudes of the non-linear coefficients of absorption and refraction have been evaluated near the bandgap wavelengths of chalcogenide glasses of the system As-S-Se by using the interferometric pump-probe method and are compared with literature data. Photoexcited plasma dynamics and long-time scale variation of the dielectric constant have been studied by comparison with the results of numerical modelling of the behaviour of the glasses when heated by the ultra-short laser pulses.

Silver diffuses into an amorphous (a-) chalcogenide layer while visible light illuminates Ag/a-chalcogenide films and neutron reflectometry is a suitable technique probing time evolution of the depth profiles without damaging the sample by the probe beam itself. In this paper, we report the results of time-resolved neutron reflectivity measurements of a-Ge₄₀Se₆₀/Ag/ Si films taken while the films are exposed to visible light. From the measurements, we found enormous changes in the neutron reflectivity profile, including a loss of total reflection region, with continuous illumination even after forming one homogeneous layer, which occurred about 50 min after starting illumination. At this stage, a clear off-specular scattering was observed by a linear detector and a surface roughness was observed with naked eyes.

Secondary optical processes are becoming more and more important in health and environmental applications. Ultraviolet produced from secondary emission or scintillation can damage DNA by direct photoexcitation or by the creation of reactive oxygen species. X-ray Excited Optical Luminescence (XEOL) and Time Resolved XEOL (TRXEOL) results for the fast emitter, CaF₂:ZnO, that have been treated by heating in air and in vacuum, show that the scintillation from the Self Trapped Exciton (STE) emission of CaF₂ at 282 nm is dominated by a slow process (>100 ns). A faster but weaker 10 ns component is also present. The ZnO and CaF2 show independent emission. The ZnO bandgap emission at 390 nm has dominant lifetimes of less than 1 ns.

We calculated "density"/"molecular weight" ratio of glass former oxides and modifier oxides to increase a number density of rare-earth ions in glass phosphor. Based on the calculated results, GeO₂ and ZnO were chosen for the glass former oxide and the modifier oxide, respectively. The effects of substituting GeO₂ for B₂O₃, ZnO for Sb₂O₃, or ZnO for Bi₂O₃ on luminescence spectra in Sm³⁺-doped glass were not observed. On the other hand, a drastically luminescence spectrum changing of Pr³⁺-doped glass was observed by substituting GeO₂ for B₂O₃. The output power of Sm³⁺ -doped glass and that of Pr³⁺ -doped glass increased with substituting ZnO for Bi₂O₃. We successfully achieved an ultra-wideband luminescence from 760 nm to 1100 nm with the output power of 2.5 mW by combining a blue LED with 0.15Sm₂O₃-0.12Pr₆O₁₁-10ZnO-45Sb₂O₃-45GeO₂ glass in one package.

Cathodoluminescence (CL) spectra have been collected from single nanometer-sized crystals of Y_1.98Tb_0.02O₂S and Gd_1.98Tb_0.02O₂S using a Gatan Vulcan cathodoluminescence imaging spectrometer. Slight variations observed in the CL spectra taken from the crystals are explained, and discussed in relation to bulk samples.

Replication of 3D-structures, in particular those that have a periodic modulation of a dielectric material at optical wavelengths and below have proven very difficult to fabricate. The majority of such replication techniques are complex or use moisture sensitive precursors requiring the use of for example a glove box. Here we demonstrate how an air stable supersaturated europium-doped yttrium nitrate phosphor precursor solution has the ability to easily impregnate a structure or produce a cast yielding faithful replicas composed of Y₂O:Eu³⁺ after a final short annealing step. New replicas of Lepidoptera (moth) wing scales using field emission scanning electron microscopy, structures down to 10 nm have been imaged. Moreover as these replicas are made of phosphors, their luminescence in some cases may be modulated by the internal periodic modulation built into their structures. In this work we will discuss more recent results on the use of the phosphors for making nanocasts of moth wing scales and show a range of beautiful pictures to show what the method can achieve.

Cathodoluminescence studies are reported of phosphors in a field emission scanning electron microscope (FESEM). A number of phosphor materials have been studied and exhibited a pronounced comet-like structure at high scan rates, because the particle continued to emit light after the beam had moved onto subsequent pixels. Image analysis has been used to study the loss of brightness along the tail and hence to determine the decay time of the materials. This technique provides a simple and convenient way to study the decay times of individual particles.

We numerically demonstrated broad and flattened gain spectra of optical parametric amplification employing highly nonlinear tellurite optical fiber and dual-pump configuration. The chromatic dispersion profile of the tellurite hybrid microstructured optical fiber was engineered to be near-zero and flattened, having four zero-dispersion wavelengths at 1421, 1643, 1928 and 2169 nm. The effect of pump wavelength was investigated when the two pump powers were kept at 1 W, the fiber length was 25 cm and the fiber nonlinearity was as high as 6642 W^-1km^-1. It is shown that OPA gain bandwidth with gain ripples could be as broad as 1393 nm at 10-dB signal gain. When the central pump wavelength approached the third zero- dispersion wavelength and the pump powers were 1.25 W, an ultra-flat (±0.01-dB gain fluctuation) and broad gain bandwidth (658 nm at 30-dB signal gain) could be achieved.

We developed a NIR absorption spectrometry system for detection of toxic substances by using a glass phosphor based LED. Using this NIR absorption spectrometry system, phosphoric acid solution samples were measured by molybdenum-blue method. Absorption band around 900 nm and that around 960 nm were observed. The absorption band around 900 nm increased with increasing of the phosphoric acid concentration. Partial least squares (PLS) analysis was revealed that a lower phosphoric acid concentration limit of 0.01 ppm. Furthermore, Cu dilute solutions were measured. Although there was no clear absorption band related to Cu, PLS analysis was revealed that a lower Cu concentration limit of 0.1 ppm. These results indicated that this NIR absorption spectrometry system is useful for practical applications.

Acousto-Optic Tunable Filters (AOTFs) are electronically-controlled bandpass optical filters. They are often preferred in applications in spectroscopy where their agility and rapid random-access tuning can be deployed to advantage. When used for spectral imaging a large aperture (typically 10mm or more) is desired in order to permit sufficient optical throughput. However, in the mid IR the λ² dependence on RF drive power combined with the large aperture can prove to be a hurdle, often making them impractical for many applications beyond about 2μm. We describe and compare a series of specialised free-space configurations of AOTF made from single crystal tellurium dioxide, that require relatively low RF drive power. We report on AOTFs specifically optimised for operation with a new generation of Supercontinuum source operating in the 2-4μm window and show how these may be used in a spectral imaging system. Finally, we describe an AOTF with an (acoustic) Fabry-Perot cavity operating at acoustic resonance rather than the conventional travelling-wave mode; the acoustic power requirement therefore being reduced. We present an analysis of the predicted performance. In addition, we address the practical issues in deploying such a scheme and outline the design of a prototype "resonant AOTF" operating in the 1-2μm region.

The films based on the low-molecular amorphous azochromophore 2-(3-(4-((4- (Ethyl(2-(trityloxy)ethyl)amino)phenyl)diazenyl)styryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile (IWK-2M) were prepared. The optical properties of the material, such as transmittance and reflection spectra of the film, sensitivity to polarization holographic recording by two wavelengths (405 and 532 nm) were studied. The direct relief formation during the polarization holographic recording was explored, relief depth dependence on exposure and record beam intensity was investigated. The holographic matrix on this material base was produced without chemical etching process; the replication of holographic image was performed.

Epitaxial thin films of indium tin oxide (ITO) were grown on yttria-stabilized zirconia single-crystal substrates by using a pulsed laser deposition to examine their plasmonic properties. The dielectric function of ITO was characterized by spectroscopic ellipsometry. Through the concentration of SnO₂ in the target, the carrier concentration in the films was modified, which directly leads to the tuning of the dielectric function in the near-infrared region. Variable-angle reflectance spectroscopy in the Kretschmann geometry shows the dip in the reflection spectrum of p-polarized light corresponding to the excitation of surface plasmon polaritions (SPPs) in the near-infrared region. The excitation wavelength of the SPPs was shifted with changing the dielectric functions of ITO, which is reproduced by the calculation using transfer matrix method.

Recently it has been demonstrated that chiral metamaterials show giant optical activity and circular dichroism. However, it has been rarely known about rotational force generated by incident wave in chiral metamaterials. We calculate the rotational force in the bilayered gammadion chiral metamaterial. In addition, we show that a bi-layered structure, which has greater optical activity than a single-layered structure, changes the rotational force tendency greatly. This result can be used as a possible optical manipulation in biological sciences.

In this paper, we demonstrate an enhancement to SPW cavity through the incorporation of high-Q WGM bottle microresonator (BMR) with surface microgrooves. A standard BMR fabricated through the "soften-and-compress" technique with initial length of 280 μm, bottle diameter of 187 μm and stem diameter of 125 μm was utilized in the experiment for supporting WGMs. Thin gold film was deposited on top of the BMR for generating SPWs. 21 microgrooves was then inscribed on the metal surface of the BMR along the azimuthal direction with 10 μm length, 485 nm width, 6 μm depth and pitch of 1.5 μm. Due to surface curvature, the gold film only covered half of the BMR with a characteristic meniscus shape and maximum thickness of 30 nm. The meniscus provides appropriately tapered metal edges that facilitate the adiabatic transformation of BMR WGMs to SPWs and vice-versa. Lorentzian shape-line fit performed on the TM excited resonances show that plasmonic Q values in excess of 4000 could be achieved from such structure with ∼ 25% coupling efficiency.

We theoretically examine the optical responses of two molecules near gold nanoblocks which generate strongly localized near-fields due to localized surface plasmon resonance. The molecules located in the near-fields efficiently interact with light. As a result, we find that correlations between the molecules exist, even though the molecules are distantly positioned. Because these correlations are of importance to collective behaviors of the molecules such as superradiance and superfluorescence, this result implies the possibility of these collective behaviors being generated through the plasmonic fields. Besides, correlations between molecules must be taken into account with regards to device applications of metallic nanostructure arrays.