Preparation And Fluorescence Properties Of Sr₄Al₂O₇ Based Red Phosphor

Researches shows that the energy consumption in the lighting field occupies a large part of the energy consumption system.With the world energy crisis and environmental pollution problem becoming more and more serious,people urgently need to find a new type of green lighting equipment.White-light emitting diodes?WLEDS?is considered as the fourth generation solid-state lighting with advantages of high light efficiency,low power consumption,small size,long life and environmentally friendly.The most popular way to achieve WLED is the phosphor coating chip method,the current commercial WLED obtained by combinating UV chip and YAG:Ce powder which is of high color temperatureand low color rendering index due to the lack of red light components,thus can not meet the requirements of indoor use.Phosphor is an indispensable part of the white LED,directly affect the white LED color temperature,color rendering index,luminous efficiency and life expectancy.Therefore,investigations have been mainly focused on the development of novel red emitting phosphors.Aluminate-based phosphors have attracted more and more attention because of their simple preparation method,low cost of raw materials,stable crystal structure and good optical properties.In this paper,a series of rare-earth Eu ions doped Sr₄Al₂O₇ red phosphors were synthesized by high-temperature solid state reaction method,and factors which influence the morphology,phase and spectral properties of phosphors were investigated to get optimal preparation process.The spectral properties of Eu ions doped Sr₄Al₂O₇: Eu²⁺ were investigated,and the luminescent behavior of Eu in the matrix was studied.The influence of crystal field on the luminescence properties was further demonstrated by the doping of alkaline earth ions.Finally,AlN and NH₄ I is introducted to promote the reduction of Eu³⁺ in Sr₄Al₂O₇ phosphors and the efficiency of Eu²⁺ emission is greatly improved.The main work can be summarized as the following:?1?Eu-doped Sr₄Al₂O₇ red phosphors were synthesized by high temperature solid-state reaction method based on SrO-Al₂O₃ binary phase diagram analysis.By changing the milling time,calcination temperature and holding time,artificially control the composition phase and particle morphology and get the best synthesis process.?2?The luminescence behavior of Eu ions in Sr₄Al₂O₇ matrix was systematically studied.In the Sr₄Al₂O₇ matrix,Eu ions occupy different Sr ion sites and Eu³⁺ can only be partially reduced to Eu²⁺.The excitation spectrum of Eu²⁺ doped Sr₄Al₂O₇ sample exhibits a wide spectrum?400nm-500nm?covering the near-ultraviolet to blue region,which can be well matched with near UV and blue chip.?3?The luminescence of Ba²⁺/Ca²⁺ substitutting for Sr²⁺ in Sr₄Al₂O₇:Eu²⁺ samples was studied.The intensity of the fluorescence spectra was enhanced by the substitution of alkali metal ions.The emission spectra of the phosphors were blue-shifted by Ba²⁺ substitution while red-shifted by Ca²⁺ substitution.?4?The luminescent properties of AlN doped Sr₄Al₂O₇:Eu²⁺ samples under different atmospheres were studied.In the process of sintering,some of the N₃-and Eu³⁺ react as follows: 2N₃-+6Eu³⁺?6Eu²⁺+ N₂?,so the introduction of N₃-can effectively promote the reduction of Eu³⁺,thus improving the emission intensity of the phosphor?5?The luminescent properties of NH₄I-doped ?-Sr₄Al₂O₇ samples were studied.The pure ? phase can be synthesized at the sintering temperature of 1300?,but there just exits the characteristic emission of Eu³⁺.The characteristic emission of Eu²⁺ in NH₄I-doped ?-Sr₄Al₂O₇ samples was observed,and its luminescent intensity was enhanced with the increase of NH₄ I content.It was suggested that the addition of NH₄ I effectively promoted the reduction of Eu³⁺ to Eu²⁺,and the reaction mechanism might be:NH₄I?NH³⁺HI;6HI+Eu₂O₃?2EuI³⁺H₂O?,EuI₃?EuI₂+I₂?.