| Compared with incandescent lamps, fluorescent lamps and mercury lamps, whiteLEDs(light emitting diode, LED) have advantages of high electro-optic conversionefficiency, long persistence, energy saving, small volume and so on. Therefore, thewhite LED is believed to be a future generation solid-state lighting source. At present,the most commonly used white LEDs are made by means of blue LED chip coveredby yellow powder phosphors and packaged with epoxy resin. However, this kindwhite LEDs basically suffer some weaknesses such as low chromatic stability, poorcolor rendering index, poor heat-resistance, aging resistance and moisture resistancewhich affect the reliability of white LED devices. Glasses have advantages of hightransparency, stable performance, easy formation and so on. So glasses become goodmatrix materials. In order to improve the luminous efficiency and reliability of whiteLED devices, glass ceramic phosphors have been investigated as alternatives topowder phosphors. Therefore, it is significant in LED theory and application to studythe luminescent properties of coating of phosphor P2O5-ZnO-B2O3glass.In this paper, Low-melting-point glass powders of P2O5-ZnO-B2O3(PZB) wereused as matrix, mixed with yttrium aluminum garnet crystals containing Ce (YAG:Cephosphors), solvent and binder. After stirring well, glass paste was made and coatedon glass substrate by screen printing, then sintered for the preparation of phosphorPZB glass coating. Using X-ray diffraction, Raman spectra, absorption spectra andfluorescence spectrometer, the effects of YAG:Ce phosphors mole fraction,phosphorus pentoxide content, sintering temperature on structure and luminescentproperties were studied. The results show that:1. The influencing factors of the structure of the coating of phosphor PZB glass:with an increasing mole fraction of P2O5,the amount of [PO4] and [BO4]groups increased. the stretching vibration of P=O groups and the symmetricstretching vibration of P-O-P groups were strengthen. The band at about1050cm-1was assigned as the symmetric stretching vibration of O-P-O unitsshifted towards higher wavelength; As the doping quantity of YAG:Cephosphors increased, the amount of YAG phased increase too, the amount of Zn2P2O7and BPO4phases remained basically unchanged; With theincreasing sintering temperature, the amount of YAG phases were notchanged much and the amount of BPO4phases decreased. When thesintering temperature increased from550℃to600℃，transformation ofZn2P2O7occured.2. The excitation spectra of the phosphor glass coating was taken for emission at543nm and showed a double peak structure which located at around340nm and460nm. The emission spectra was recorded for excitation at460nm and showed a broademission peak at around550nm.3. With the increasing YAG:Ce phosphors doping quantity, the intensities ofluminescence spectras increased first and then decreased. The light transmittance ofthe phosphor glass coating decreased；As the sintering temperature increased, theintensities of luminescence spectras increased first and then decreased. The lighttransmittance of samples increased.4. In this experiment, the suitable YAG:Ce phosphors doping quantity was25%and the sintering temperature was600℃.5. The luminescence decay time of phosphor PZB glass coating was around1.5μs. As the YAG:Ce phosphors content increased from10%to25%, theluminescence lifetime increased from1.52μs to1.558μs. The luminescence lifetimedecreased with the sintering temperature.6. The chemical stability of glass was studied using weight loss method.According to the national standards GB/T171129-1997，The water resistance of thematrix glass is in the third category and the phosphor glass is in the second category. |
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