Synthesis Of Alkaline Earth Metal Bromine Phosphate Phosphor And Theoretical Study On Defect Controlled Luminescence

Inorganic solid luminescent materials（commonly known as phosphors）are an important part of solid-state lighting devices.Self-activated phosphors controlled by intrinsic defects are an important class of inorganic luminescent materials.Intrinsic defect-related luminescence for the use of modified phosphors has recently attracted increasing research interest.However,the relationship between defect formation and crystal structure has not been considered in detail.Therefore,an in-depth understanding of the formation process of intrinsic point defects and the electronic structure of defective unit cells is of great significance for the development of novel self-activated phosphors.The strategy of doping rare earth ions or transition metal ions into an optically inactive host to achieve luminescence is the most common route to obtain inorganic phosphors of various luminescent colors.Then,if the rare earth ions are doped into the self-activated luminescent host and the doping concentration is changed,it is likely that a series of fine tunable phosphors will be obtained,which provides new ideas for us to explore new phosphors.1.Self-activated luminescence and defect luminescence mechanism of（Ca,Sr,Ba）5（PO4）3Br.In the absence of an impurity activator,under a reducing atmosphere,apatite-type compound M₅（PO₄）₃Br（M=Ca,Sr,or Ba）can emit tunable colors ranging from blue to orange depending on the content of M.To better understand the cause,Ba_5-mSr_m（PO₄）₃Br（BSPOB;m=0-5）solid solutions were analyzed in detail.The dependency of self-activated luminescence on atmospheric conditions and solid solution compositionswasinvestigatedbycombiningexperimental characterizations and theoretical calculations using density functional theory.Crystal structures of these solid solutions were verified by X-ray diffraction patterns as well as Rietveld refinements.With the defect formation energy and electron paramagnetic resonance measurement,we propose that an oxygen vacancy（V_O）should be mainly responsible for the peculiar super wide band emission.Moreover,the enhanced distortion of solid solution crystal structures augments V_O concentrations and leads to luminescence intensities in solid solutions that are higher than that in end point compounds.Variations of the electronic structure of BSPOB matrices with gradual tuning of the Sr/Ba ratio were also investigated.As a result,the introduction of V_O defect levels within the band gap leads to the formation of donors and acceptors,allowing for a modulation of the photoluminescence throughout the visible part of the spectrum.As the first report in the literature to demonstrate fine-tunable emissions over a wide wavelength range as a consequence of native defective levels in a series of continuous apatite-type solid solutions,our results illustrate the feasibility of defect-meditated systems by carefully tailoring defect chemistry and nonstoichiometric chemical composition under controlled conditions to engineer phosphor properties.2.Defect-regulated（Ba,Sr）₅（PO₄）₃Br:Eu²⁺multi-color phosphor.The alkaline earth metal bromine phosphate phosphors doped with different concentrations of Eu²⁺were synthesized by high temperature solid phase method.The luminescence properties of BSPOB endpoint compounds and intermediate solid solution doped with different concentrations of Eu²⁺was investigated.The occupancy of Eu²⁺in the apatite structure was further analyzed according to the photoluminescence emission spectrum characteristics,temperature-dependence of photoluminescence behavior spectra and luminescence decay curves.In addition,based on the self-activated intrinsic defect luminescence of the BSPOB host,when a series of low concentration of Eu²⁺is doped,the modulating emission of the spectrum from yellow-green light to white light to blue light can be realized with the change of Eu²⁺concentration.Combined with the fluorescence decay curve,it is reasonable to conclude that luminescence is derived from the self-activated luminescence of the host and the luminescence of Eu²⁺.