Study On The Property Of Flower-alike Pr³⁺-activated Sr₃Al₂O₆ Orange-reddish Long Afterglow Luminescent Phosphors And Investigation Of The Luminescence Mechanism

Long afterglow luminescent materials,with the characterization of photoluminescence and light energy storage,can be used as energy storage-saving materials,but also as advanced materials for targeting drug delivery and data storaging.Long afterglow luminescent materials were systematically investigated,and their preparation,structure and luminescence mechanism were classified and summarized in this work.The strontium aluminate Sr₃Al₂O₆ materials with stable chemical properties,high quantum efficiency and large energy gap were explored as matrix material,and rare earth ions Pr³⁺as activators.The orange-reddish persistent luminescent materials of Sr₃Al₂O₆:Pr³⁺,Sr₃Al₂O₆:Pr³⁺,Sm³⁺and Sr₃Al₂O₆:Pr³⁺,Dy³⁺were prepared by high temperature solid state method in air atmosphere.The structure and luminescence properties of the prepared materials were characterized and analyzed by the XRD,SEM,EDS,XPS,UV-visible absorption spectra,excitation and emission spectra,decay curves and thermoluminescence(TL)spectra.Based on the analysis of the microstructure and performance of the materials,the luminescence mechanisms of the material were constructed,the factors of improving the luminescence performances of the materials were explored,some innovative work was made and many meaningful research results were achieved.(1)Pr³⁺activated Sr₃Al₂O₆ orange-reddish long-lasting phosphors with the shape of flower-alike were obtained by high temperature solid state reaction,which belonged to the cubic phase(PDF#24-1187)of Sr₃Al₂O₆.The direct band gap of the measured material is 5.32 eV.There existed an absorption assigned to f-d transition of Pr³⁺in the ultraviolet region and the localized energy levels were generated in the host lattice.The emission peaks at 560,612,626-634,650-659,714,740 and 761 nm were attributed to 3P1?3HJ(J=5,6),3P0?3HJ(J=5,6),1D2?3HJ(J=4,5)and 3P0?3FJ(J=2,3,4)transitions of Pr³⁺ respectively.According to the analysis of XPS measurements and defect equations,it inferred that there could exist Vo··?VSr"?VAl'''?Oi"?PrSr· and PrSr·· defects,as well as[PrSr·-Oi"-PrSr·]/[PrSr··-Oi"-PrSr··]defect clusters in the material lattices.The prepared material can effectively store light and improve the luminescence performance due to its appropriate depths of 0.73 eV,0.76 eV and 0.83 eV and high trap concentration.The afterglow time can last for 6 h.EPR analysis confirmed the fact that electrons were trapped by defects and released by thermal vibration.The electron-hole pairs luminescence mechanism was constructed through the energy band theory and the crystal defect theory(2)The luminescence properties of Sr₃Al₂O₆:Pr³⁺ materials were effectively improved by co-doping Sm³⁺ions.There existed the defects of Vo··?PrSr·?PrSr·· and SmSr·,and the defect clusters of[PrSr·-Oi"-PrSr·]/[PrSr··-Oi"-PrSr··]/[SmSr·-Oi"-SmSr·]in the material lattices.Sm³⁺co-doped Sr₃Al₂O₆:Pr³⁺materials were obtained with the effective trap level depth of 0.76 eV and 0.78 eV,and significant increase of the trap concentrations,for increasing the ability of capturing carriers,extending the life span of electron-hole pairs and greatly improving the luminescence properties of the materials with the longest afterglow time of 17 h.Based on the energy band theory and defect theory,the luminescence mechanism of Sm³⁺co-doped long afterglow materials was established(3)Dy³⁺co-doping can effectively improve the luminescence properties of Sr₃Al₂O₆:Pr³⁺materials.Dy³⁺ions paly the triple function roles as luminescence centers,defect suppliers and sensitized ions.The emission spectra showed that the orange-reddish luminescence of materials came from the main contribution of the f-f transition of Pr³⁺,and some contribution of the 4F9/2?6H13/2(602-622 nm)and 4F9/2?6H11/2(720-786 nm)transitions of Dy³⁺.In addition,since there exists partial overlaps between the emission peaks of Dy³⁺and the excition peaks of Pr³⁺,the energy transfer from Dy³⁺to Pr³⁺occurs,which may also contributes to the luminescence performence of the materials.Dy³⁺and Pr³⁺/Pr4+co-doping would produce Vo··?PrSr·?PrSr·· and DySr· defects along with[PrSr·-Oi"-PrSr·]/[PrSr··-Oi·-PrSr··]/[DySr·-Oi"-DySr·]defect clusters,effectively increased the trap energy level concentration,heigthened the ability to capture carriers,obviously enhanced the luminous properties of materials with the afterglow time of 10 h.According to the energy band theory and the defect theory,the luminescence mechanism of the material was built.