| Since 1993, the Niehia Company developed the white LED based on the InGaN chip. A lighting revolution is sweeping all over the world after the first White LED (InGaN/Y3Al5O12:Ce3+) was reported in 1996. As a new solid-state light source, the white light emitting diode (W-LED) has been widely used in backlighting for liquid crystal displays and incandescent lamps due to its low power consumption, environmental friendliness, long lifetime, compact size, etc. White-light generation through GaN based light-emitting diode LED has a number of advantages over the existing incandescent and halogen lamps in power efficiency, reliability, and long lifetime.The most commonly used approach to generate white light relies on the combination of blue LED with yellow phosphor (YAG:Ce3+). However, this approach has because of the lack of sufficient red component, as well as poor thermal stability. To overcome these deficiencies, a combination of UV LED with red-green-blue (RGB) phosphors has been suggested. Unfortunately, light-resorption limits the improvement of luminescence efficiency and CRI. Thus, more and more attention has been paid to the strategy of the combination of white emitting phosphor with UV/NUV chip because of its excellent stability of light-emitting, and its simple fabrication process.Silicates are excellent hosts for photoluminescence materials for their low-cost and high physical-chemical stability. The advantages for UV/NUV chip with silicate phosphor are oxidation resisting and arid. Eu3+ and Tb3+ ions with sharp lines are originated from fâ†'f transitions. Then, the broad absorption and emission bands, which are believed to be associated with the electronic dâ†'f transition of the Eu2+ions. It is well known that the dâ†'f transition of Eu2+is strongly affected by the around crystallography environment, which results in red shift or blue shift of emission peak. It is possible to obtain a single-phase phosphor by co-doping Eu3+, Eu2+, Tb3+ions and adjusting luminescence color.This paper intends to obtain phoshors for white LED by high temperature solid state reaction which can be excited by UV/NUV light and research excellent optical properties. We have synthesized two different single-phase silicate phosphors. One is Eu3- and Tb3+ions co-doped in Sr1.5Ca0.5Si04 orthosilicate, the other one is Tb3+ions doping Sr2MgSi207 mesosilicate. We studied the preparation condition and discussed the luminescent mechanism.1. Synthesis and luminescent properties of Ca2-xSiO4:Eu2+green phosphorsGreen phosphors were synthesized by high temperature solid state reaction calcined at 1250℃. Comparison of XRD, SEM and luminescent intensity of samples shows that the phase purity and luminescent intensity can be improved by replace SiO2 with H2SiO3 at 1250℃.2. Synthesis and luminescent properties of Sr2-xCaxSiO4:Eu2+(x= 0-1.95)Samples Sr1.95.xCaxSiO4:0.5%Eu2+(x=0-1.95) were synthesized at different temperature (1200℃,1250℃). It is found from the analysis results of XRD and luminescent properties. The competition between crystal field splitting and the nephelauxetic effect, which result in red or blue shift of emission peak.3. Phosphor Sr1.5Ca0.5SiO4:Eu3+,Eu2+,Tb3+luminescent properties and mechanismPrepared Sr1.5Ca0.5SiO4:Eu3+,Eu2+phosphor, and investigated the relationship of sample about reaction time and luminescent intensity when Eu3+ions were reduced partially to Eu2+ions. We found that the green emission band of Sr1.5Ca0.5SiO4:Tb3+ was originated from the 4fâ†'4f transition of Tb3+ ions. Under carbon reduction condition, it was possible to obtain single-phase White Light-Emitting phosphor Sr1.5 Ca0.5SiO4:Eu3+, Eu2+,Tb3+for LED-Based Near-UV Chip. The energy transfer occurred from Eu2+ions to Tb3+ion.4. The luminescence properties of Tb3+ doped crystal Sr2MgSi2O7Single-phase White Light-Emitting phosphor Sr2MgSi2O7:Tb3+ was synthesized by high temperature solid state reaction. We found when Tb3+ mole fraction is greater than 20%, the host crystal lattice would be distorted, and result in luminescent intensity reduction. |
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