Preparation And Performance Of Glass Ceramics By Compositing Red Phosphor Filme For White LED

As the fourth generation lighting source, white LEDs have been widely used in the fields of indoor and outdoor lighting, due to their advantages of energy saving, environmental protection, long service life,low voltage, fast response and so on. The current w-LED structure by packing the YAG:Ce3+ phosphor dispersed in silicone or epoxy resin(phosphor-in-silicone, PiS) on the InGaN blue chip. However, there are three problems with this package: 1) thermal conductivity of the traditional organic packaging materials is too poor and easy to aging after long-term heat radiation in the work environment, easily causing serious discoloration and luminescent degradation; 2) refractive index mismatch of YAG:Ce3+ phosphor particles and organic packaging materials can also lead to loss of light scattering; 3) the absence of red emissive component in the YAG:Ce3+ results in the low color rendering index, high corrected color temperature, which can not get warm white. Therefore, the study of an ideal color-converting material with excellent color quality and durable reliability becomes especially significant and meaningful in long-lifetime high-power warm w-LEDs.This project created a combination of red phosphor coating and fluorescent glass: the fluorescent glass with excellent heat/chemical stability and optical properties was prepared, and then coated with red phosphor coating by screen printing on the glass substrate. The red phosphor coating stacked PiG plate (R-PiG) based w-LED is encapsulated to make white. The developed R-PiG color converter not only include the advantages of glass matrix with high thermal conductivity, excellent light transmittance and physicochemical stability,but also overcome the disadvantages of the traditional white LED with short life, the refractive index mismatch. Moreover, a facile chromaticity tuning for the thus-fabricated LED by the screen-printing technique was achieved. The main research contents are as follows:(1) Based on the previous experiment, transparent LuAG:Ce3+fluorescent glass (PiG) were prepared by one step using low temperature co-sintering method and then white LED device was constructed by coupling the PiG plate stacked with CaAlSiN3:Eu2+ red phosphor coating on commercial InGaN LED. The pre-prepared LuAG:Ce3+ fluorescent glass was chatractered by XRD, SEM and fluorescence spectrum to analyze its phase, microstructure and luminescent property, and its thermal stability test shows that the the fluorescence intensity of the LuAG:Ce3+ fluorescent glass was significantly higher than that of silica encapsulated LuAG:Ce3+ in the same condition, which showed that the fluorescent glass with excellent thermal conductivity, light output,fluorescence /stable performance was successfully prepared by the one step low temperature co-sintering method. However, it is difficult to obtain the warm white light for the luorescent glass plate based w-LED whether changing the doping concentration of phosphor fluorescent glass or film thickness. Then, the screen-printing process was performed to coat CaAlSiN3:Eu2+ ink containing red phosphor onto the PiG substrate.Owing to that red emissive component gradually intensifies with increasing the red phosphor amount, the appearance of the fabricated LED evolves from cool, to natural white, and finally warm white warm light, the CCT gradually decreases and the CRI increases. Moreover, the excellent thermal stability reveals the feasibility of this color-converting material to replace the conventional organic polymer encapsulants for the high-power LED applications. Finally, uniform angular color distribution in this LED structure is poor and will be further optimized in the future.(2) In the same way, the transparent YAG:Ce3+, Ga3+ (YAGG)fluorescent glass was firstly prepared by one step low temperature co-sintering method and screen printing Ca?Si5Al8:Eu2+ red phosphor coating film on YAGG substrate into LED device package. The pre-prepared YAGG PiG was chatractered by XRD, SEM and fluorescence spectrum to analyze its phase, microstructure and luminescent property,which showed that YAGG like LuAG:Ce3+ in the glass matrix, keep good optical stability. Then, the screen-printing process was performed to coat CaAlSiN3:Eu2+ ink containing red phosphor onto the PiG substrate. We study the red phosphor concentration and coating thickness on the resist heat and luminescent propties of the red phosphor coating to find the optimal coating thickness. At the given optimal screen-printed layer thickness and 0.8 mm-thick YAGG PiG, the appearance of the fabricated LED evolves from cool, to natural white, and finally warm white warm light, the CCT gradually decreases and the CRI increases. Finally, heat-resistance test was carried out to evaluate the luminescence performance of the R-PiG fabricated warm w-LEDs and the CIE chromaticity coordinates slightly increases with heat-treatment time, the CCT and CRI have no significant variation. Those results clearly demonstrate that the developed R-PiG color converter with an excellent thermal stability can be promising for the case in the high-powered long-duration LED devices.