Luminescence Property Of Eu²⁺/Bi³⁺ Doped Aluminum/Tungstate/Gallate Phosphors For Near-ultraviolet White Light LED

As a new generation of lighting source,WLED?White Light Emitting Diode?has been widely used in our daily life.At present,the mainstream design of WLED is composed with a blue LED chip and YAG:Ce³⁺yellow phosphor.However,due to the low color rendering index and high color temperature,this solution cannot meet people's demand for high-quality lighting.The scheme of adding different colors of phosphors to near-ultraviolet?NUV?chip can overcome the above problems and achieve high quality white light.However,there is no phosphors that perfectly match near-ultraviolet excitation.Therefore,the purpose of this paper is to find the new type of phosphor for WLED that can satisfy near ultraviolet excitation.The research contents and results of this paper are as follows:?1?It was found that the cyan phosphor Sr₄Al₁₄O₂₅:Eu²⁺can be used for NUV excited WLEDsThrough the study of the luminescence properties of Sr₄Al₁₄O₂₅:Eu²⁺,it was found that the excitation spectrum of Sr₄Al₁₄O₂₅:Eu²⁺matched well with the NUV?360-410nm?chip and can be used for NUV excitation WLEDs.At the same time,the effect of different Eu²⁺concentration?0.02%-1%?on the thermal stability of Sr₄Al₁₄O₂₅:Eu²⁺was also studied.It was found that the thermal stability gradually increased with the increase of concentration,which was contrary to the relationship between the concentration and thermal stability of usual phosphor.We believe that this abnormal phenomenon may be caused by the positive correlation between the energy transfer between the two Eu²⁺luminescence centers and the temperature and concentration.In addition,it was also found that the doping of AlN and SiN can enhance the luminous intensity and initial afterglow intensity of Sr₄Al₁₄O₂₅:Eu²⁺,respectively.?2?Four new types of ultraviolet/near-ultraviolet excitation and without visible region absorption of Bi³⁺doped tungsten/gallate phosphorsFirstly,three new types of Bi³⁺doped tungstate phosphors were discovered,which are:LiY?WO₄?₂:Bi³⁺,Ca₃WO₆:Bi³⁺and La₆W₂O₁₅:Bi³⁺.The results show that their optimal excitation peaks are located at 334 nm,336 nm and 347 nm respectively,and the excitation spectrum can be extended to 390 nm,400 nm and 410 nm respectively,and there is no excitation in the visible light?VIS?region,so the problem of visible light reabsorption of traditional phosphors can be avoided.The emission spectrum of them is broadband with emission peaks at 556 nm,576 nm and 627 nm,respectively.The emission spectrum extends from 400 nm to 800 nm that cover the entire visible light region,and the full width at half maximum?FWHM?is 170 nm,160 nm and 200 nm respectively suitable for illumination.The study also found that their fluorescence lifetimes are 600 ns,370 ns and 1500 ns,respectively,which all belong to the characteristic lifetime of Bi³⁺,so the luminescence is likely to come from the transition of³P₁?¹S₀ in Bi³⁺.In addition,we also synthesized a Bi³⁺doped gallate phosphor:La₃SnGa₅O₁₄:Bi³⁺.We found that La₃SnGa₅O₁₄:Bi³⁺had only one excitation band and the excitation peak was at 290 nm.However,there are two emission bands with emission peaks at 356 nm and 540 nm,respectively.Among them,the broadband emission band in the visible region is considered to be abnormal emission related to Bi³⁺.Through the analysis of emission spectra of different Bi³⁺doping concentrations,low-temperature spectra,lifetime and the calculation of MMCT model,we believe that the visible broadband light emission is likely to come from the transition of ³P₀?¹S₀ in Bi³⁺,and the ultraviolet emission band is from transition of ³P₁?¹S₀ in Bi³⁺.This work is helpful for the in-depth understanding of Bi³⁺doped solid luminescent materials and the development of Bi³⁺doped phosphors.The results show that the Bi³⁺doped tungsten/gallate phosphor found in this paper has potential applications in UV/NUV excitation WLED.This paper contains 46 pictures,3 tables and 182 references.