Investigation Of Preparation And Photoluminescence Properties Of Phosphors Used For Near Ultraviolet And/or Blue LEDs

White light emitting diodes (WLEDs) have attracted many attentions of researcher in recent years due to high luminous efficiency, energy savings, long persistence, environmental friendliness, small volume and lack of toxic mercury. Two basic approaches can be used to fabricate white LEDs. The conventional approach is the combination of near ultraviolet or blue light LED chips with photo convert phosphors. In this thesis, the phosphors have been summarized in detail firstly. Because of some disadvantages of present phosphors, such as poor chemical stability, low efficiency or critical synthesis conditions, novel phosphors or preparation methods have to be developed.In this thesis, Eu2+ and Mn2+ codoped Ba2Mg(BO3)2, Eu2+ doped oxyapatite-like oxysilicates Mx-yLn10-xSi6027-x/2 (M= Mg, Ca, Sr, Ba, Ln= Y, La, Gd) and its oxynitrides, Eu2+ doped Sr2Si5Ng have been prepared by high temperature solid state at different synthesis conditions and their photoluminescence properties have been investigated in detail.In present work, the phase structure of Eu2+ and Mn2+ codoped Ba2Mg(BO3)2 phosphors were determined by XRD. The phosphors emit orangish-red light under 365 nm excitation. By photoluminescence spectra and decay time measurements, the effect of Mn2+ on photoluminescence properties has been investigated in detail. The results show that Mn2+ don't act as activators but purify long wavelength emission of Eu2+ and thus the tunable orangish-yellow to orangish-red emission is obtained by varying Mn2+ concentration.Eu2+ doped oxyapatite-like oxysilicates phosphors with general chemical formula Mx-yLn10-xSi6O27-x/2:Eu2+ have been successfully synthesized by studying the firing conditions. The effect of firing temperature on phase structure and photoluminescence properties have been studied and then the optimized temperature was obtained. By the measurements of photoluminescence spectra, the effect of M2+ ions, Ln ions, M2+ ions concentrations and Eu2+ concentration on photoluminescence spectra have been investigated in detail. These phosphors show broad excitation bands ranging from 280-450 nm and exhibit from bluish-green to orange light under 365 nm excitation. The emissions of Eu2+ at different crystallographic sites have been discussed. The results show that short wavelength emission band attributes to the emission of Eu2+ at 4f site and long wavelength to that of Eu2+ at 6h site. The energy transfer between Eu2+ at two sites has been discussed. By SEM, the morphology and particle size has been determined and the results show that the phosphors have good crystallization with super fine size. Introduction of N3- generally leads to redshift emission of Eu2+, therefore, oxyapatite-like oxysilicates above mentioned have been prepared under NH3 atmosphere. The effect of Sr resources on nitrogen content, phase structure and photoluminescence properties have been studied by O/N analyzer, XRD and photoluminescence spectra. The results suggest that the phosphor using SrCN2:Eu as Sr resource exhibits higher emission intensity than that of using SrCO3. The Effect of firing temperature on phase structure of phosphors using SrCN2:Eu as starting materials have been investigated in detail and the solid state reaction process has been discussed by XRD measurements. For investigating the mechanism of Eu2+ emission, the effect of temperature at the range of 69-325K on photoluminescence spectra have been studied. The results indicate that two distinguished emission bands can be observed clearly and blueshift of long wavelength emission occurs with increasing temperature but short wavelength emission don't change except for temperature quenching. The possible mechanism has been discussed.Sr2Si5N8:Eu2+ is a excellent red emission phosphor for WLEDs application. In present work, Sr2Si5N8:Eu2+ phosphor has been synthesized at low temperature by using SrCN2:Eu as starting materials under NH3 atmosphere. The phase, nitrogen content and photoluminescence properties of Sr2Si5N8:Eu2+ phosphor have been determined by XRD, O/N analyzer and photoluminescence spectra. Blueshift of emission band was observed and the mechanism has been discussed.Due to playing a key role in preparing oxynitrides and nitrides above mentioned, Eu2+ doped MCN2 (Ca,Sr) with different Eu2+ contents were prepared by high temperature solid state reaction under NH3 atmosphere. The phase structures have been determined by XRD spectra. Because of potential photoluminescence ability, the optical properties and photoluminescence spectra at low temperature of SrCN2:Eu have been investigated in detail. The results show that SrCN2 has an energy gap of 4.56 eV by the reflection spectra and Eu2+ doped SrCN2 shows a broad band emission with a peak at 610 nm when it is excited by 350-520 nm at 77 K. With the temperature increasing, the emission intensity decreases remarkably, indicating that Eu2+ doped SrCN2 has a low quenching temperature. The temperature quenching mechanism has been investigated.