Synthesis, Structure And Luminescence Property Of Tungstates Red Phosphors-used On WLED

White light emitting diodes (WLEDs) have been considered as the mostpromising green lighting optical source for the fourth generation due to the merit of along operation lifetime, energy conservation and non-pollution. Presently, the generalapproach to fabricate WLED is to combine a near ultra violet or blue LED chip with ayellow-emitting phosphor or red phosphors which have been commercial. Therefore,it is crucial to synthesize red phosphors which excitation wavelength is matched withthe emission of commercial LED chips to improve the efficiency of white light LEDdevices.In this paper, tungstate red phosphors Sr3ln2W09:Eu3十andLaEuBW+i-xMox09:Eu3were prepared by using solid-state reaction. The X-raydiffraction, photoluminescence and FESEM were used to characterize the crystalstructure，optical property and morphology. The effect of sinteirng temperature,holding time, concentration of activator and amount of Mo6+on crystal structure andoptical property of the phosphors are investigated. The details are as follows.The efifcient red phosphor of SdIiuWOvEu3. has been synthesized. Thesynthesis condition is optimized by orthogonal-experiment as sintering the rawmaterials under1000°C for12h. Under this condition, the pure phase and crystalproduct was obtained，which present efifcient photoluminescence deirved fromhypersensitivity transition of Eu3+at617nm, In the excitation spectra, a broadexcitation band of charge transfer (CT) ranging rfom250to350nm. What’s more, thecharacteirstic excitation of sharp line of Eu3+at396and466nm are prominentlybroadened. The quenching concentration of activator is up to25%, which is higher than most phosphors. It is demonstrated that Eu3+is located at the site of In3+by X-raydiffraction and photoluminescence. Under the same measurement condition, theluminescence intensity of Sr3ln2W09:Eu3+is1.6times higher than Y2O2S: Eu3+andthe color coordinate (0.65,0.32) is close to the standard red. The excellentluminescent performance and uniform grain size made il suitable as a high-efficiencyred phosphor used in UNV or blue LED chip.Under the sythesis condition of1000°C for24h optimized byorthogonal-experiment, the red phosphor of LajBWi.xMoxOviEu3has been prepared.The information of the cell parameters, atom coordinate and bond distance arcobtained by crystal structure refinement of X-ray difrraction. XRD and PL show thatwhen the doping concentration of Mo6" is up to30%, the single phase ofLajBW1-xMox09：Eu3+is retained and the optimum luminescence performance ispresented. In this doping amount+of Mo6, the volume of unit cell is shirnking andexcitation spectra is shitfed to the longer wavelength with increasing of Mo6二Thepeak shitfed from305to375nm and its intensity improved30%. The energy gap ofLa^..BW]XMOxOq:Hu3+is calculatcd by CASPF program based on density functiontheory (DFT) of the first principle. It is found that after Mo6+doped, energy gapdecreased from2,93eV to2,55eV of the material, which is agreement to the resultcalculated from absorption spectra. The quenching concentration of Euu activator is10%. In addition, it is found that the wide excitation band is due to the chargetransmission between valence band made up of0-2p character and conductive bandof Mo-4d or W-5d character.. Compared with Y2O2S: Eu3at627nm (the highest placein its emission spectra), the luminescent intensity at617nm is increased about6times.The grain size of the red phosphors analysized by SEM is about2|im. In a word, thedoping of Mo6+improved th’e phosphors efficiency and made it match better with theLED chips on the market.The efficient red phosphors of tungstates may find their promising applicationfor WLED due to the chcmical stability, nontoxic and environment firendly.