Typical CCD image sensors are not sensitive to Ultra-Violet (UV) radiation, because the UV photons have a penetration depth of 2nm in the ~1µm thick polysilicon gate material. An inorganic phosphor coating was developed previously (by Wendy Franks et al [1, 2]) that was shown to be a viable solution to creating a UV-sensitive CCD image sensor. The coating absorbs incident UV radiation (250nm) and re-emits it in the visible (550-611nm) where it can penetrate the gate material. This coating was deposited using a settle-coat type deposition. Improved coating techniques are presented here. These include a commercial coating from Applied Scintillation Technologies (AST), a Doctor-Blade coating, e-beam deposition, and laser ablation. The properties of the coating, and of the coated sensors are presented here. Tests performed on the sensors include Quantum Efficiency, Photo-Response Non-Uniformity, Contrast Transfer Function, and Lifetime. The AST coating is a viable method for commercial UV-responsive CCD image sensors. The Doctor-Blade coatings show promise, but issues with clustering of the coating need to be resolved before the sensors can be used commercially. E-beam deposition and laser ablation need further research to provide a viable coating.

Typical CCD image sensors are not sensitive to Ultra-Violet (UV) radiation, because the UV photons have a penetration depth of 2nm in the ~1µm thick polysilicon gate material. An inorganic phosphor coating was developed previously (by Wendy Franks et al [1, 2]) that was shown to be a viable solution to creating a UV-sensitive CCD image sensor. The coating absorbs incident UV radiation (250nm) and re-emits it in the visible (550-611nm) where it can penetrate the gate material. This coating was deposited using a settle-coat type deposition. Improved coating techniques are presented here. These include a commercial coating from Applied Scintillation Technologies (AST), a Doctor-Blade coating, e-beam deposition, and laser ablation. The properties of the coating, and of the coated sensors are presented here. Tests performed on the sensors include Quantum Efficiency, Photo-Response Non-Uniformity, Contrast Transfer Function, and Lifetime. The AST coating is a viable method for commercial UV-responsive CCD image sensors. The Doctor-Blade coatings show promise, but issues with clustering of the coating need to be resolved before the sensors can be used commercially. E-beam deposition and laser ablation need further research to provide a viable coating.

Si QDs embedded in SiOx or SiNx thin films, which could emit light in the entire visible range from 440 nm to 840 nm by controlling their size and/or their matrix, were synthesized by evaporation or plasma enhanced chemical vapor deposition techniques. Various shades of white could be obtained from multi-layered SiNx film structures by controlling the size of Si QDs and layer thickness. It was shown that the combination of these films can produce white emission spectra with superior color rendering properties compared to conventional fluorescent tubes. Such Si-based QDs can be used as down-converting phosphors to coat a blue/UV LED to generate white light, providing a less expensive fabrication process to obtain advanced solid state lighting devices. As a supplement, free CdTe QDs with emission colors spanning 520~700 nm and quantum efficiency up to 54%, were synthesized using a colloidal chemical method for white LED applications. White PL and a range of emission colors were obtained from mixed CdTe QD samples excited by a 420 nm blue LED. Another part of this research was to develop a new x-ray powder phosphor, ZnTe:O, for biological imaging applications used in CCD-based synchrotron x-ray detectors. A unique dry synthesis process, including gaseous dry doping and etching procedures, was developed to synthesize ZnTe:O phosphors. The excellent x-ray luminescence results of oxygen doped ZnTe, including high efficiency, high resolution, fast decay, low afterglow and an improved spectral match to the CCD detector, indicated that ZnTe:O is a promising phosphor candidate for x-ray imaging applications.

High thermal stability and humidity resistance of phosphor-converted white-light-emitting diodes (PC-WLEDs) using Ce:YAG doped glass, instead of conventional Ce:YAG doped silicone, as a phosphor-converted layer is proposed and fabricated. The glass has five times higher glass transition temperature (Tg) of 750¢J compare with silicone of 150¢J, that could exhibited better performance than silicone, including lumen loss, chromaticity shift, transmittance loss, and peak emission intensity undergoing three industry-standard reliability tests at either high (8wt%) or low (2wt%) doping concentrations of Ce:YAG. The proposed glass phosphor possesses host stability as glass and retains desired fluorescence as Ce:YAG. In thermal aging, thermal shock, and damp heat reliability results, the thermal aging has the largest degradation of lumen loss, but the results showed better thermal stability that the glass phosphor with 22~30% lumen loss improvement for 2~8 wt% Ce:YAG doping than silicone phosphor. The damp heat test has the largest degradation of chromaticity shift, but the results showed excellent humidity resistance that the glass phosphor with highest 49~65% chromaticity shift improvement for 2~8 wt% Ce:YAG doping than silicone phosphor. But under thermal shock test, there isn¡¦t a large difference between glass and silicone phosphor. In this study, we demonstrate the feasibility of adapting glass as a phosphor-converted layer in PC-WLED module that can potentially provide higher reliability and better performance for high-power LEDs, particularly in the area where strict reliability is highly required and in the environment where silicone does not stand for long.

A Ce:YAG-doped glass phosphor layer instead of conventional Ce:YAG-doped silicone phosphor layer as phosphor-converted white-light emitting diodes (PC-WLEDs) is demonstrated. The advantage of employing doped glass encapsulation in high power PC-WLEDs could be explained the material property of glass transition temperature of 750¢J was higher than silicone of 150¢J. The lumen degradation, chromaticity shift, color temperature change, transmittance, and fluorescence spectrum in glass and silicone based high-power PC-WLEDs under thermal aging at 150¢J, 200¢J, and 250¢J is compared and presented. Under highest temperature of 250¢J, the glass and silicone encapsulation base d PC-WLEDs exhibited 8.15% and 38.85% in lumen loss, 1.07 and 7.32 in chromaticity shift, 856 K and 3666 K in color temperature change, 4.21% and 28.1% in transmittance loss, respectively. However, the excitation spectrum altered as slight as emission spectrum before and after experiments. After aging test, the mean-time-to-failure (MTTF) evaluation of glass and silicone encapsulation materials for PC-WLEDs in accelerated thermal tests is also compared and presented by the using of Weibull distribution and Arrhenius equation. The MTTF of PC-WLEDs is defined the lumen decayed to 90%. The results showed that the glass as encapsulation material of PC-WLEDs exhibited higher MTTF than the silicone encapsulation by about 4.81, 5.92, and 7.53 times in lumen loss at 150¢J, 200¢J, and 250¢J, respectively. The results of the lumen loss, chromaticity shift, and MTTF investigations demonstrated that the thermal-stability performance of the glass based PC-WLEDs were better than silicone based PC-WLEDs at 150¢J, 200¢J, and 250¢J. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.

This paper tries to explore the phosphor optical characteristics through reliability tests using white light emitting diodes (WLEDs) with a high color rendering index (CRI ,Ra¡Ö90). Based on light mixing principles and considering the high CRI, three color-coded powders were mixed separately with silicone into a phosphor, and then bottomed with blue chips into WLEDs. The three powders were oxide nitride (red), YAG (yellow), and silicate (green). Two kinds of samples were fabricated ¡V phosphor and emitters similar to commercial products. Both cool-white (CCT=5650~7000K, lumen efficiency¡Ö60 lum/w.) and warm-white (CCT=2850~3250K, lumen efficiency¡Ö50 lum/w.) samples passed the Bin Code distribution process and brightness measurement. The results indicate better lumen efficiency than previously published research. After the three kinds of mono-colored phosphors were created, .we implemented the reliability test in which three CREE standards were chosen. These standards were (1) high temperature with high humidity test (60¢J , 90% humidity) in operating and non-operating condition; (2) thermal shock test (-40¢J ~125¢J ); (3) life time test. The thermal shock test showed the decaying power of intensity for red, yellow, and green phosphors were 11.7%, 17.5%, and 19.3% respectively. These results demonstrate that the red phosphor has the best thermal resistance. However, after the high temperature with high humidity tests, the decaying power of intensity for red,yellow, and green phosphor were 15.7%, 10.1% and 6.4% correspondingly. These results show that the green phosphor has best aqua resistance. In the life time test of emitters, the decaying power of intensity for the cool-white emitter was 3.2%, while the warm-white emitter showed 4.2%. As such, cool-white emitters were concluded to have better reliability than warm-white emitters.

Diss. Nr. 12807 Naturwiss. ETH Zürich. / Literaturverz.

Universiẗat, Diss., 2000--Osnabrück.

Universiẗat, Diss., 1998--Kaiserslautern.

Universiẗat, Diss., 2001--Osnabrück.