Research On Preparation And Luminescence Properties Of Novel Red Fluorescent Materials Based On The Matrix Of A_xIn_2-x（MoO₄）₃（A=Gd/Sc） Abnormal Expansion Materials

As a solid-state light-emitting device,Light Emitting Diode（LED）has the advantages of high efficiency and energy saving,environmental protection,lightness and convenient,etc,which can be widely used in transportation,agriculture,medical,aviation and other fields.Ultraviolet excitation fluorescent materials have become one of the research hotspots in recent years.However,the current commercial ultraviolet excited red phosphors(Y₂O₂S:Eu³⁺,Y₂O₃:Eu³⁺)have some shortcomings in chemical stability,luminescence properties.Moreover,due to the high ultraviolet energy emitted by ultraviolet chips,the energy accumulation is serious,which is easy to cause thermal quenching.Therefore,it is urgent to explore new red fluorescent materials excited by ultraviolet light,which is expected to have high thermal stability particularly.In the paper,A_xIn_2-x（MoO₄）₃（A=Gd/Sc）was selected as the matrix and Eu³⁺as the rare earth doped luminescent ion in the abnormal expansion material.Two new red fluorescent materials Gd_0.3In_1.7（MoO₄）₃:Eu³⁺and In_0.5Sc_1.5（MoO₄）₃:Eu³⁺with high thermal stability,high color rendering index and excitation wavelength matching with commercial LED chips were developed.Their structure and luminescence properties were analyzed by testing and characterization,which have excellent luminescence properties and thermal stability.The specific research results were as follows:（1）Gd_0.3In_1.7（MoO₄）₃:Eu³⁺phosphors with different Eu³⁺doping concentrations were synthesized by high temperature solid-state method in air atmosphere.By X-ray powder diffraction and Rietveld structure refinement,it was found that with the increase of Eu³⁺doping concentration,the structure of compound changed from cubic phase to monoclinic phase.The Eu³⁺occupied In³⁺site was inferred by the bond energy method.The theoretical calculation and experimental results showed that the band gap value of the phosphor was between 2.86-3.54 e V,and the band gap decreased with the increase of Eu³⁺doping concentration.The strongest emission peak of the phosphor was located at 615 nm under the excitation of 394 nm and 465 nm,which belonged to the energy level transition of ⁵D₀→⁷F₂ of Eu³⁺ion.It also had the characteristics of anti-concentration quenching,and the value of concentration quenching was as high as 90mol%,the overall color purity was higher than 99.17%.The color coordinate（0.6645,0.3352）of the optimal phosphor Gd_0.3In_1.7（MoO₄）₃:80mol%Eu³⁺was close to the ideal red color coordinate（0.670,0.330）,the internal quantum efficiency was 78.07%under the excitation of 394nm,and the fluorescence lifetime was about 718μs.Its thermal stability under ultraviolet excitation（83.3%@423K）was better than that of commercial red phosphors（74%@423K）,more prominently,the integrated emission intensity of Gd_0.3In_1.7（MoO₄）₃:30mol%Eu³⁺（106.3%@423K）and 80mol%Eu³⁺（111.5%@423K）samples at 150°C showed excellent performance of near-zero thermal quenching and negative thermal quenching compared with room temperature.The LED devices made by encapsulating the phosphor with commercial ultraviolet chips and blue chips coud emit bright red light.The results showed that Gd_0.3In_1.7（MoO₄）₃:Eu³⁺was new fluorescent material with excellent properties such as anti-thermal quenching,anti-concentration quenching and high color rendering index.（2）Based on the matrix of In_0.5Sc_1.5（MoO₄）₃ with negative thermal expansion in the wide temperature range,In_0.5Sc_1.5（MoO₄）₃:Eu³⁺phosphors with different Eu³⁺doping concentrations were synthesized by high temperature solid-state method.The XRD results showed that In_0.5Sc_1.5（MoO₄）₃:Eu³⁺pure phase has been synthesized.The main emission peak of the phosphor was at 615 nm under ultraviolet excitation,which was attributed to the ⁵D₀-⁷F₂ energy level transition of Eu³⁺.The fluorescence lifetime of the phosphor was 297-493μs.Its quenching concentration was 8 mol%.The nonradiative energy transfer mechanism between Eu³⁺was mainly exchange interaction.The internal quantum efficiency of In_0.5Sc_1.5（MoO₄）₃:8mol%Eu³⁺phosphor was 57.8%,and the overall color purity was as high as 99.52%,the chromaticity coordinates of the phosphor was（0.668,0339）.Compared with commercial red phosphor Y₂O₃:0.05Eu³⁺（0.62,0.37）,it was closer to the ideal red light（0.670,0.330）.At the same time,the phosphor could maintain the good characteristics of near-zero thermal quenching in the temperature range from room temperature to 250°C,and its thermal stability was better than that of commercial red phosphor（74%@423K）.The LED device packaged with commercial ultraviolet LED chip could emit bright red light at120 m A bias current.The results showed that In_0.5Sc_1.5（MoO₄）₃:Eu³⁺was new red fluorescent material with high thermal stability and high color rendering index,and its comprehensive performance was better than that of commercial ultraviolet excited red phosphors.