In this paper, we report anatase and rutile titanium oxide (TiO2) nanoparticulate thin films fabricated on silica and Indium Tin Oxide (ITO) substrates using femtosecond pulsed laser deposition (fs-PLD). Depositions were carried-out at substrate temperatures of 25 °C, 400 °C and 600 °C from anatase and rutile phase target materials. Effect of substrate temperature on the surface morphology, microstructural, optical, and electrical properties of these films were systematically investigated by using various range of measurements such as scanning electron microscopy, (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Ultraviolet–visible-near infrared (UV–Vis–NIR) spectroscopy, and Hall Effect measurements. It is observed that the TiO2 thin films surface are predominated with nanoparticulates of diameter less 35 nm, which constitute about ~ 70%; while the optical bandgaps and electrical resistivity decrease with increasing substrate temperature. A mixed-phase (anatase/rutile) TiO2 thin film was produced at a substrate temperature of 400 °C when samples are fabricated with anatase and rutile target materials. The results of this study indicate that the structural and crystallinity, optical, and electrical properties can be controlled by varying fs-PLD process parameters to prepare TiO2 thin films, which are suitable for applications in photovoltaics, solar cells, and photo-catalysis.

A study on the preparation of thermally stable phosphor targets based on yttrium aluminium garnet doped with cerium (YAG:Ce) when excited by a high power laser diode is described. The luminous flux, chromaticity and Radial spectral flux of the targets along with their thermal stability have been determined when exposed to laser powers of up to 5000mW. This report presents successful high brightness light sources with adjustable emission properties achieved by utilising thermally stable phosphor targets excited by high power laser diodes.

The presence of voltage controlled negative differential resistance was observed in conduction characteristics recorded at room temperature for 300 nm thick spin-coated films of graphene oxide (GO) sandwiched between indium tin oxide (ITO) substrates and top electrodes of sputtered gold (Au) film. The GO crystallites were found from the X-ray diffraction studies to have an average size in the order of 7.24 nm and to be preferentially oriented along (001) plane. Raman spectroscopy suggested that the material consisted of multilayer stacks with the defects being located at the edges with an average distance of 1.04 nm apart. UV visible spectroscopy studies suggested that the band gap of the material was 4.3 eV, corresponding to direct transitions. The two-terminal ITO/GO/Au devices exhibited memristor characteristics with scan-rate dependent hysteresis, threshold voltage and On/Off ratios. A value of >10 4 was obtained for On/Off ratio at a scan rate of 400 mVs −1 and 4.2 V.

Laser diodes have the potential of becoming the light engines of future lighting technology since they have negligible efficiency droop factor, unlike light emitting diodes. This study demonstrates the possibility of laser diodes coupled to phosphor targets being used as a solid state lighting system with high power applications. It was revealed that white light emitting modules with efficiency of up to 217 lumens per watt based on laser diodes can currently be made and upon further development of laser diode technology and relevant phosphor materials there is room for further improvements. The report also demonstrates the ability of this technology to produce a tailored emission spectrum for a given specific requirement. Two test lamp prototypes were made using laser diodes and phosphor targets and their emission characteristics were investigated. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0101603jss] All rights reserved. Currently light emitting diodes (LEDs) coupled with phosphors are the most efficient source of solid state white light provided that they are operated at low input powers. The drop in the LED's efficiency at higher input powers is associated to a phenomenon called the efficiency droop. This phenomenon has been investigated for the past decade and is thought to be linked to the Auger effect.1-3 Despite extensive research in to the field no fundamental or definitive solution has been put forward to eliminate this effect. To achieve more lumens per power consumed, the LEDs are typically operated under higher input powers at the expense of efficiency.An alternative approach is to use Laser Diodes (LDs) in combination with the same phosphors applied in LED lighting but packaged differently to achieve high performance and efficient solid state lighting (SSL). The LDs are operated under stimulated emission and the mechanisms of efficiency droop are clamped at their lasing threshold. 4 This concludes that through application of LDs, higher efficiencies at higher input power densities can be achieved. The LDs are more efficient in this respect because they are operated by stimulated emission. At lasing threshold, all the recombination processes (The Auger, Shockley-Read-Hall mechanism & spontaneous) are clamped and additional carriers injected into the light quantum wells contribute only to stimulated emission, so it can be argued that unless a fix to the efficiency droop which is an intrinsic issue is found, the LDs will be competing with LEDs for the future of high brightness/high power SSL modules.5 Figure 1 demonstrates a comparison of the power conversion efficiency (PCE) of LDs and LEDs and what is expected in terms of performance improvement from them in future. Future LEDs will require modules which have a shift in PCE ...

The photometric properties of an radio frequency (RF)-based sputtering plasma source were monitored through optical spectroscopy. The colour of the plasma source was deduced based on conventional chromaticity index analysis and it was compared to the direct spectral data plots of the emission peaks to investigate the possibility of characterising the plasma based on its specific colour and exploring the potential of defining a new method by which the plasma sputtering process can be addressed based on the plasma colour parameters. The intention of this investigation is to evaluate the possibility of simplifying the monitoring and assessment of the sputtering process for applied scientists operating plasma sputter deposition systems. We demonstrate a viable potential for this technique in terms of providing information regarding the stability of the plasma, chamber pressure, and plasma power; however, further work is underway to verify and assess a relationship between the quality of the thin film coating and the colour characteristics of the deposition plasma. Here, we only focus on the feasibility of such an approach and demonstrate interesting observations. We observed a linear relationship between the colour functions and the plasma power, while the stability of the sputtering plasma can be assessed based on the plasma colour functions. The colour functions also follow a unique pattern when the working gas pressure is increased.

Zn 1-x Cd x :Cu 0.03% ,Cl (where x = 0.5-0.9) infrared emitting phosphors have been synthesized by an aqueous thermal decomposition method. The aim was to developing infrared emitting phosphors for coding, marking, and identification applications. The phosphors were characterized by, X-ray powder diffraction, scanning electron microscopy and photoluminescence spectroscopy. The emission band at 1000 nm was sufficiently far into the infrared region that visible emission was minimized. Co-doping Zn 1-x Cd x S:Cu 0.03% with Al 3+ increased the infrared emission intensity to over twice that of the equivalent Zn 0.3 Cd 0.7 S:Cu 0.03% phosphor (with no Al 3+ ion co-doping), with the highest intensity being found for the phosphor composition Zn 0.1 Cd 0.9 S:Cu 0.03%, Al 0.03% . It is shown herein that the inclusion of Al 3+ into the phosphors causes the formation of cells with smaller cell volume, and it is suggested that this is the prerequisite for the improved photoluminescent properties. Finally we have shown herein that these infrared emitting powder phosphors are thus able to meet marking and coding requirements, especially in low light and poor visibility. Although the uses of phosphors are widespread in modern technologies and they are common in the display and lighting industries where products find applications in both domestic and commercial applications, their use in other areas is less widely appreciated. Such uses include:-on postage stamps to help letter sorting, on currency and bank notes for secrecy/authenticity, thermometry, luminescent paints and glow in the dark toys. In addition there are a number of military applications.Recently the wide availability of near-ultraviolet light and visible light emitting diodes (LEDs) and laser diodes in addition to infrared emitting systems has made the remote excitation of infrared emitting phosphors a practical possibility. Infrared emitting powder phosphors have the potential to meet marking and coding requirements, especially in low light and poor visibility.The advantages of IR emitting powder phosphors are:-1) That they can be easily deposited by conventional techniques to form large areas, if required, either by simple settling techniques, or by inclusion in a binder suitable for screen or ink-jet printing (the binder of course must be transparent over the required spectral range). 2) Such deposited powder layers, depending on their thickness and particle size and particle morphology etc., can be used in a transmission or a reflective mode with suitable UV or visible excitation sources.The ease of fabrication and the wide excitation spectra of the phosphors as well as their efficiencies facilitate a wide range of potential applications, including the following as preliminary examples: a) For use in coding/marking systems as simple IR sensitive markers. b) For improved marking/detection in conjunction with night vision systems.The origins of the green luminescence in ZnS:Cu phosphors (where Cu is introduced as a dopant into the ZnS lattice) has been attribute...

Single crystal CVD diamond has many desirable properties compared to current, well developed, detector materials; exceptional radiation, chemical and physical hardness, chemical inertness, low Z (close to human tissue, good for dosimetry), wide bandgap and an intrinsic pathway to fast neutron detection through the 12 C(n,α) 9 Be reaction. However effective exploitation of these properties requires development of a suitable metallisation scheme to give stable contacts for high temperature applications. To best utilise available processing techniques to optimise sensor response through geometry and conversion media configurations, a reliable model is required. This must assess the performance in terms of spectral response and overall efficiency as a function of detector and converter geometry. The same is also required for proper interpretation of experimental data. Sensors have been fabricated with varying metallisation schemes indented to permit high temperature operation; Present test results indicate that viable fabrication schemes for high temperature contacts have been developed and present modelling results, supported by preliminary data from partners indicate simulations provide a useful representation of response.

The spectral properties and colour functions of a radio frequency (RF)-based sputtering plasma source was monitored during consecutive sputter deposition of zinc doped indium oxide (IZO) thin films under argon and argon/hydrogen mix. The effect of target exposure to the hydrogen gas on charge density/mobility and spectral transmittance of the deposited films was investigated. We demonstrate that consecutive exposure to the hydrogen gas during the deposition process progressively affects the properties of thin films with a certain degree of continuous improvement in electrical conductivity while demonstrating that reverting to only argon from argon/ hydrogen mix follows a complex pathway, which has not been reported previously in such detail to our knowledge. We then demonstrate that this effect can be used to prepare highly conductive zinc oxide thin films without indium presence and as such eliminating the need for the expensive indium addition. We shall demonstrate that complexity observed in emission spectra can be simply identified by monitoring the colour of the plasma through its colour functions, making this technique a simple real-time monitoring method for the deposition process.