Preparation And Luminescent Properties Of Li-based Molybadates Red Phosphors

The White LED which is the Green light source of the 21st century has become the future diection of the development of lighting for its advantages like small size,fast respons,energy saving and encironment friendly.However,the red phosphors has become a restrictive factor for the development of white LED as its poor performance in preparing and light emitting efficiency.Therefore,The study on red p hosphors matching to commerical chips is of great significance in theory and practice.A series of LiLa_1-x-x Eu_x?MoO₄?₂ red-emitting phosphors were synthesized by conventional solid-state reaction.And the effect of Calination temperature,Eu³⁺doped concentration on the phosphors'micro-structure and luminescent properties of LiLa_1-xEu_x?MoO₄?₂ were studied.It was found that the appropriate calcination temperture is825^oC;The XRD characterization indicate that LiLa_1-x-x Eu_x?MoO₄?₂ and LiLa?MoO₄?₂share the same structure,and all of them are tetragonal system.The emission intensity of the samples enhances with the increase of Eu³⁺doping concentration,and no concentration quenching was observed.On the basis of the research mentioned before,the effect of pre-heated on the micro-structure and luminscent properties of LiLa_1-x-x Eu_x?MoO₄?₂ was studied in the present work.The results shows that pre-heated don't change the crystal structure of the samples;however,the microtopography of LiLa_1-x-x Eu_x?MoO₄?₂ was optimized,the broken grain decrease and the surface of the grain become smooth and compact;meanwhile the emitting intensity of the samples were significant improved,and the appropriate temperature is 650^oC.A series of LiY_1-x-x Eu_x?MoO₄?₂ red-emitting phosphors were synthesized by conventional solid-state reaction.It was found that the appropriate calcination temperture is 950^oC;The efects of Eu³⁺doping concentration on the luminescent properties of LiY_1-x-x Eu_x?MoO₄?₂ were systematically studied,the results shows that the emitting intensity of the samples enhances with the increase of Eu³⁺doping concentration,and no concentration quenching was observed;The XRD characterization indicates that LiY_1-x-x Eu_x?MoO₄?₂ are tetragonal system.The effect of La³⁺/Y³⁺replacement on the properties of LiLa_0.91-x.91-x Y_x Eu_0.91?MoO₄?₂was studied in this paper.It was found that the crystal structure was not influenced by the x value on the replacement of La³⁺/Y³⁺,all of them are tetragonal system;However,this iron change causes a greater distortion of lattice;Besides,the effect of La³⁺/Y³⁺iron change on the grain shape was greater,too.The sample presents different microtopography with different x volue.The emitting intensity of LiLa_0.91-xY_x Eu_0.91?MoO₄?₂ is improved in various degrees by the iron change,and the biggest intensity appeared when x volue is 0.3 and 0.7.The LiLa_1-x-x Eu_x?MoO₄?₂,LiY_1-x-x Eu_x?MoO₄?₂ and LiLa_0.91-x.91-x Y_x Eu_0.91?MoO₄?₂ red emitting phosphors show strong excitation band near UV region?around 395nm?and Blue region?around 466nm?.Upon excitation of them,the phorsphors show strong red emission lines at 617nm,Which is ascribed to the forced electric dipole transition of5D0?7F2.Hence,those red phosphors can well match with the ultraviolet and blue light LED chips currently in use.The prepared samples are potential red phosphors for White LEDs application.