Solid State Phenomena Vols. 124-126

Abstract: Transparent fresnoite(Ba2TiSi2O8) glass-ceramics considered as a new type of non-linear optical materials have been prepared by controlled heat treatment in the system xK2O-(33.3-x)BaO-16.7TiO2-50SiO2(0≤x≤20 mol%), and optical properties were investigated. The glassy nature was analyzed by differential thermal analyses. The transparency of glass-ceramics was variable and controllable by the processing parameters like time and temperature. The transparent glass-ceramics showed second harmonic generation (SHG) when irradiated by a 1064nm laser beam (Nd:YAG). The SHG intensity was compared with a Y-cut α-quartz plate.

Abstract: In this paper we report on the effects of variables in thermal resistance measurement of high power GaN-based light-emitting diodes (LEDs). The investigated variables include ambient temperature, thermal interface material (TIMs) at different pressure. The combination of transient thermal measurement method and optical measurement was employed for the study. The measured thermal resistance of LED packages was found to increase with the ambient temperature. The temperature dependence of optical efficiency, forward voltage, and thermal properties of packaging materials are thought to be responsible for the increase of thermal resistance with the ambient temperature. The interface effect on the thermal resistance was studied by applying different external pressure on the interface with different TIMs. And the measured thermal resistances were found to reach stabilization at certain pressure level after initial decrease with the external applied pressure.

Abstract: 70TeO2-30WO3 glass thin films were fabricated using radio-frequency magnetron sputtering method and the effects of processing parameters on the growth rate, the surface morphologies, the crystallinity, and refractive indices of thin films have been investigated using AFM, XRD, SEM, and UV-Vis-IR spectrometer. Amorphous glass thin films with surface roughness of 4~6 nm could be formed only at room temperature and crystalline WO3 phase was observed in all the films prepared at above the room temperature. The deposition rate strongly depended on the processing parameters. It increased with increasing rf power and with decreasing processing pressure. Especially, it changed remarkably as varying the Ar/O2 gas flow ratio from 40sccm/0sccm to 0sccm/40sccm. When the films were formed in pure Ar atmosphere it shows a deposition rate of ~0.2 μm/h, whereas ~1.5 μm/h when the films was formed in pure O2 atmosphere. The refractive indices of TeO2-WO3glass thin films could be measured to be about 1.849~2.165 depending on the wavelength in the range of 500-1100 nm and the bandgap energy of glass thin film was ~3.34 eV.

Abstract: The efficient detection method based on nanostructured photonic DBR PSi has been developed for DMMP, which is a simulant for G-type nerve agents. The manufactured DBR PSi chip exhibits a sharp photonic band gap at 520 nm. The detection method involves the shift of DBR peak in reflectivity spectra under the exposure of vapors of analyte. Rapid detection has been achieved in few seconds, in situ, and observed by the red-shift of DBR peak resulted from the increase of refractive indices in DBR PSi. When DBR PSi chip is exposed to DMMP, TEP, and DEEP-saturated air, DBR peak in reflectivity is red shifted by 10 nm, 25 nm, and 10 nm, respectively. Real-time detection for the nerve gases indicates that the measurement is reversible. Detection limit of DMMP (1.5 ppm) using DBR PSi is 8.8 mg/m3 for 1 min.

Abstract: The nanostructural and optical features of Al-doped Si thin films, which were prepared by co-sputtering Al-chips and a Si main target, were investigated in terms of Al-doping and post-deposition heat-treatment conditions; the heat treatment was carried out at temperatures of 400 ~ 1100 °C. The structural and chemical features are related with the photoluminescence (PL) phenomena of the films. The PL intensity as well as the concentration of Si nanocrystallites were increased by doping particular amount of Al in the films.

Abstract: We have synthesized a Eu2+-activated Sr3MgSi2O8 blue phosphor and (Sr,Ba)2SiO4 yellow phosphor. We fabricated a phosphor-conversion white light emitting diode(LED) using an InGaN chip that emits 400 nm near-ultraviolet(n-UV) light and phosphors that emit in the blue and yellow region. When the white LED was operated at a forward-bias current of 20 mA at room temperature(RT), the color temperature(Tcp), average color rendering(Ra), operating voltage(Vf) and luminous efficacy(ηL) were estimated to be 5800K, 72.08, 3.4V, and 7.61 lm/W, respectively. The commission International de I’Eclarirage(CIE) chromaticity coordinates obtained from the measured spectra remained almost constant during the forward-baias current increase from 0.5 mA to 60 mA.

Abstract: Inductively coupled plasma reactive ion etching of Ge doped silica glasses and SiON was investigated, using C2F6- and NF3-based gas mixtures. Mesas with smooth surfaces and vertical sidewalls were obtained, with a maximum etch rate of about 310nm/min in the case of C2F6 RIE of Ge-SiO2 and 280 nm/min in the case of SiON. The NF3 plasma yielded slightly higher etch rate, although sloped sidewalls were obtained. Results of the X-ray photoelectron spectroscopy showed little contamination on the etched surfaces.

Abstract: In this paper, we present the imaging parameters and compare both mercuric iodide (HgI2) and amorphous selenium (a-Se) films. Using MCNPX code, we designed the film structure and its thickness for the optimized detector in the diagnostic x-ray range. The mercuric iodide film was formed by a wet binder process, while the amorphous selenium film was deposited by physical vapor deposition (PVD). These deposition methods are capable of being scaled up to sizes required in diagnostic imaging applications. The electronic properties are investigated using dark current, x-ray sensitivity and signal to noise ratio (SNR). From our results, the developed HgI2 film as an alternative to a-Se photoconductor, which is in practical use in flat panel x-ray imaging detector, will prove its usefulness in the future design and the optimization for various diagnostic modalities.

Abstract: We have synthesized a Eu2+-activated lanthanide co-doped Sr3SiO5 : Eu yellow-orange phosphor. In this experiment, sample powder has been synthesized by conventional solid state method. It was calculated that luminescent efficiency of a Gd3+ co-doped Sr3SiO5:Eu phosphor sample is up to 105% than that of only Sr3SiO5:Eu phosphor. Those samples can be applied such as phosphor for white LED lamps through integrating on the UV or blue chips. On the contrary, the use of a Dy, Ce, Pr and lanthanide short of Gd by the co-doping materials was caused by decreasing luminescent intensity. The emission band was shifted from 572nm to short wavelengths by co-doping lanthanide. The emission band of a Nd3+ co-doped Sr3SiO5 : Eu phosphor sample was not symmetrical at 570nm. As Nd3+ concentration increased, two emission bands were observed

Abstract: Si and Er co-doped SiO2 films were fabricated by radio-frequency (RF) magnetron sputtering technique with a Si-Er-SiO2 target. The optical gain of 0.7 dB/cm was confirmed by the direct pumping of Er3+ using the laser diode (LD) of 980 nm in wavelength and 60 mW in output power. On the contrary, the pumping Si-nanocrystals by the Hg lamp 365 nm (1.5 W/cm2) induced the absorption loss above 1.48 μm region in wavelength, which was attributed to the free carrier absorption of Si-nanocrystals.