Study On Luminescence Properties Of Red-emitting Phosphors With Indium And GdNbO₄for White Light Emitting Diodes

White light emitting diodes （white LED） used as white light sources have attractedmore attention because of their many advantages such as long lifetime, low energycomsumption and environmental friendliness. Phosphor-converted white LEDs are themain methods to obtain white LEDs. The white light must include red light compositionin order to improve the quality of white light. So red phosphors play an important rolein the white LED. At present, red phosphors are mainly made of sulphides andoxysulfides. Because they have low luminescence efficiency and less chemical stable, ithas become the one of restraining factors. Aiming at the above state, the content of thisproject is to exploit the high performance red phosphors. The red phosphors withindium and GdNbO₄were prepared by the high temperature solid-state reaction. Theirluminescence properties and mechanism were also investigated for the purpose ofwidening the rearch on the red phosphors for white LED.The matrix compounds consit of lanthanum indate, indium niobate, tungstates andmolybdates, which are doped by Eu³⁺, Pr³⁺and Sm³⁺ions. The relative results are asfollows.（1） The emission spectrum of LaInO₃:Eu³⁺has two strong absorption sharp lineslocated at394nm and464nm. When the phosphor is excited by the above lights, it canemit the red light at610nm which originates from⁵D₀→⁷F₂of Eu³⁺. Theluminescence intensity of the phosphor reaches the maxium when the concentration ofEu³⁺is20mol%. Once the concentration is beyond20mol%, the intensity drops due tothe concentration quenching. According to the theory of Dexter, the self-quenchingmechanism of Eu³⁺in the LaInO₃host results from the quadripole-quadripole reaction.The luminescence intensity doped with Bi³⁺will be improved because of the sensitiveeffect of Bi³⁺on the Eu³⁺. The best concentration of Bi³⁺is3mol%. There are twostrong excitation peaks in the phosphor LaInO₃:Sm³⁺, which are respectively at405nm,460-480nm. They consist with the output wavelengths of LED chips, so this phosphorcan be excited by the LED chips. LaInO₃:Sm³⁺emits the orange red light at600nm andthe PL intensity reaches the maxium under the4mol%concentration of Sm³⁺.（2） InNbO₄:Eu³⁺has two excitation wavelengths which include394nm and466nm,which can emit red light at612nm. The4mol%concentration of doping Eu³⁺makes theluminescence intensity achieve the maximal value. The PL intensities of the phosphors InNb1.6P0.4O₄:0.04Eu³⁺and InNb0.9Ta0.1O₄:0.04Eu³⁺are higher than that ofthe phosphor InNbO₄:0.04Eu³⁺due to the additions of P and Ta elements. The spectrumof the phosphor InNbO₄:Pr has some sharp lines from449nm to470nm. The emissionspectrum has two peaks located at603nm and614nm excited at466nm, which indicatesthat it can be excited by blue light to emit red light. The PL intensity achieves themaxium when the concentration of Pr is0.3mol%. For the phosphor InNbO₄:Eu³⁺,Sm³⁺,there is a absorption peak at405nm in the excitation spectrum, which results of theenergy transition of⁶H_5/2→⁴K_11/2of Sm³⁺. In the emission spectrum, threre is nopeak of Sm³⁺emission and the strong peak of Eu³⁺emission at612nm is observed, thusit illustrates that the energy transition ofSm³⁺→Eu³⁺exits and the PL intensityincreases with the Sm³⁺increasing. InNbO₄:0.05Eu³⁺,0.05Sm³⁺is an ideal phosphor inthe matter of PL intensity. The photoluminescence intensity ofIn_0.91Gd_0.05NbO₄:0.04Eu³⁺is better than the phosphor InNbO₄:0.04Eu³⁺because of theGd element addition.（3） In₂（MoO₄）₃:Eu³⁺can be efficiently excited by the395nm and466nm lights toemit strong red light at612nm. The photoluminescence intensity of the phoshphor withthe40mol%concentration of Eu³⁺is the best and its CIE chromaticity coordinates are（0.63,0.35） and （0.60,0.38） respectively excited at395nm and466nm, which is close tothe pure red light. With the addition of3mol%Bi³⁺in the phosphor In₂（MoO₄）₃:0.4Eu³⁺,the phosphor In₂（MoO₄）₃:0.4Eu³⁺,0.03Bi³⁺has good PL intensity. For the phosphorIn₂（MoO₄）₃:Eu³⁺,Sm³⁺, its excitation spectrum is widened at the scope of thenear-ultraviolet light and PL intensity is better than the phosphor In₂（MoO₄）₃:Eu³⁺. SoIn₂（MoO₄）₃:Eu³⁺,0.04Sm³⁺is a good phosphor for white LED. The intensity of thephosphor In_1.6（WO₄）x（MoO₄）₃-x:0.4Eu³⁺is higher than the In_1.6（MoO₄）₃:0.4Eu³⁺when xvalue is0.04owing to the W element addition. The phosphor In₂-x（WO₄）₃:xEu³⁺canabsorb the energy of the light at395nm and466nm to emit red light at611nm, whichillustrates that In₂（WO₄）₃:Eu³⁺is a potential red phosphor for white LEDThe research on the series of GdNbO₄:Eu³⁺shows there exit394nm and464nmexcitation peaks in the excitation spectrum. Because the Eu³⁺is located in a asymmetriccation environment of the lattice, the intensity of electric dipole transition for the Eu³⁺at612nm is obviously stronger than that of magnetic dipole transition. Compared withdifferent content of Eu³⁺, the phosphor Gd_0.8NbO₄:0.2Eu³⁺belongs to a better phosphor.The PL intensity of the Gd_0.8NbO₄:0.2Eu³⁺with the addition of In element increases andthe Gd_0.78In_0.02NbO₄:0.2Eu³⁺is suggested as the best phosphor among the Gd_0.78-xIn_xNbO₄:0.2Eu³⁺phosphors. Compared with the Gd_0.8NbO₄:0.2Eu³⁺, theintensity of the Gd_0.77NbO₄:0.2Eu³⁺,0.03Bi³⁺at612nm is about twice stronger than theGd_0.8NbO₄:0.2Eu³⁺. Based on the Gd_0.77NbO₄:0.2Eu³⁺,0.03Bi³⁺constituent, thephosphor Gd_0.78In_0.01NbO₄:0.2Eu³⁺,0.01Sm³⁺was synthesized. The CIE chromaticitycoordinates of Gd_0.78In_0.01NbO₄:0.2Eu³⁺,0.01Sm³⁺are x=0.64, y=0.36under theexcitation of the light at395nm and its color is close to pure red light. From the aboveresults, it can be concluded that the phosphor Gd_0.78In_0.01NbO₄:0.2Eu³⁺,0.01Sm³⁺is thebest photoluminescence material for the white LED.