Preparation And Properties Of Double Perovskite Tungsten-Molybdate Phosphors

The energy problem has always been an important issue that has to be faced on the way of economic development and social progress,so the solution to the global energy crisis is urgent.Light-emitting diode（LED）has become an excellent emerging light source to replace incandescent lamps and other traditional light sources because of its high luminous efficiency and better energy efficiency.And tungsten-molybdate has excellent physical and chemical stability.In addition,tungsten-molybdate is one of the research hotspots for LED fluorescent materials,which has a charge transfer of O^2-→W⁶⁺/Mo⁶⁺in the near-UV region,exhibiting a broad excitation peak.In this paper,the phosphors based on Sr2Ca WO6 with double perovskite structure and doped with Eu³⁺,Dy³⁺,Sm³⁺in Ca²⁺lattice position were prepared by high-temperature solid-phase method.And Sr2Ca Mo O6 as a substrate,doped with Eu³⁺in Ca²⁺lattice position.And the Sr2Ca（W1-y Moy）O6:Eu³⁺phosphors with better performance were obtained by the gradual substitution of tungsten ions to molybdenum ions.The phosphors doped with Eu³⁺,Sm³⁺and Pr³⁺in the lattice position of Zn²⁺were prepared using Ba2Zn WO6 as the substrate.The properties of the samples were characterized by various testing methods.The specific experimental results were as follows:（1）The sintering temperature and time of the samples prepared by high-temperature solid-phase method were 1300℃and 6 h,respectively.（2）The GSAS structure refinement of Sr2Ca WO6:Eu³⁺sample determined that the rare earth ion Eu³⁺entered the Ca²⁺lattice of Sr2Ca WO6 crystal and occupied the octahedral lattic e of Ca²⁺/O^2-with high symmetry.The excitation peaks of Sr₂Ca WO₆:Re³⁺(Eu³⁺,Dy³⁺,Sm³⁺)were mainly in the charge transfer band（CTB）.The reason of concentration quenching wa s electric dipole-electric dipole interaction by fitting.All three phosphors had good thermal st ability.The fluorescence lifetime of the samples with the best concentration was obtained by testing and fitting.The compensating charges（M=Li⁺,Na⁺,K⁺）was introduced into Sr2Ca W O₆:Re³⁺(Eu³⁺,Dy³⁺,Sm³⁺)to improve the luminescence performance of the samples,and the luminescence performance of phosphors was the best when Na⁺was used as the compensati ng charge.（3）The excitation peak of Sr2Ca Mo O6:Eu³⁺phosphor was located near 397 nm in the near-UV region,and the main emission peak was located at 596 nm attributing to the magnetic dipole transition.When the Ca²⁺site was replaced by Eu³⁺,the best luminescence performance of the sample was determined when Na⁺was used as the compensating charge.In order to improve the thermal stability of Sr2Ca Mo O6:Eu³⁺,the method of gradually replacing Mo⁶⁺with W⁶⁺was adopted,and samples with excitation peaks located at 397 nm in the near-UV region were obtained with better thermal stability and higher luminescence intensity,which was higher than Sr₂Ca_0.9Mo O₆:0.1Eu³⁺phosphor of Sr₂Ca_0.9Mo_0.5W_0.5O₆:0.1Eu³⁺.（4）In Ba₂Zn WO₆:Re³⁺(Eu³⁺,Sm³⁺,Pr³⁺)phosphors,the excitation peak was located in the charge transfer band（CTB）,and the concentration quenching was caused by electric dipole-electric dipole interaction.The effect of charge compensators（M=Li⁺,Na⁺,K⁺）on the properties of Ba₂Zn WO₆:Re³⁺(Eu³⁺,Sm³⁺,Pr³⁺)was investigated under the condition that Zn²⁺lattice was replaced by rare-earth ions.It was determined that Li⁺was used as the compensation charge when Zn²⁺was replaced by three rare earth ions,and the luminescence performance was the best.