Preparation And Luminescence Regulation Of Tantalate Near Infrared Phosphor With Double Perovskite Structure

Near infrared light has an important application in the fields of security monitoring,biological medical,plant lighting,spectral detection and other fields.The traditional near infrared light source cannot meet people’s demand for quick and convenient use of near infrared equipment.Near infrared phosphor conversion LED（NIR pc-LED）can make up for the deficiency of traditional near infrared light source,and is the most promising new near infrared light source to replace the traditional near infrared light source.There are two types of octahedral lattice sites in the cells of A₂B’B’’O₆ double perovskite oxide,which can provide different doping sites for Cr³⁺ions.Its B site can be doped with two different cations,which can adjust the crystal field environment of Cr³⁺ions,thereby realizing the regulation of the emission spectrum of the near-infrared phosphor,which is a suitable near-infrared phosphor matrix.In this study,Cr³⁺ions were introduced into the tantalate double perovskite matrix Ca₂Ga Ta O₆,and a new type of tantalate double perovskite near-infrared phosphor was obtained.Its luminescence properties were analyzed,and the luminescence properties were regulated by means of energy transfer and cation substitution,which improved the application potential of double perovskite near-infrared phosphors.The contents and results of this study are as follows:（1）A series of Ca₂Ga Ta O₆:Cr³⁺double perovskite near-infrared phosphors were prepared at a reaction temperature of 1400℃by a high-temperature solid-phase method.The space group of Ca₂Ga Ta O₆:Cr³⁺is P21/n,which belongs to the monoclinic system.Under the excitation of 467 nm blue light,the emission peak of Ca₂Ga Ta O₆:Cr³⁺near-infrared phosphor is located at 750 nm,the full width at half maximum is 113 nm,the quantum efficiency is 32%,and the optimal doping concentration of Cr³⁺ions is 0.02.The emission peaks of Ca₂Ga Ta O₆:Cr³⁺are double-peak emission by Gaussian peak fitting,indicating that the proportion of Cr³⁺ions entering the two octahedral sites does not change with the increase of Cr³⁺ion doping concentration.The fluorescence lifetime is 85.17μs,which is in line with the spin allowed transition characteristics of ~4T₂→~4A₂ by the Cr³⁺.Electron paramagnetic resonance（EPR）did not find the signal peak of Cr⁴⁺ion.Through Cr³⁺→Yb³⁺co-doping energy transfer,the emission spectrum covers the region between 750 and1050 nm,and the broadening of the emission spectrum improves the application potential of Ca₂Ga Ta O₆:Cr³⁺double perovskite near-infrared phosphors.The energy transfer efficiency is 10%,and the photoelectric efficiency of the encapsulated near-infrared LED is 4.5%.（2）The effect of cation substitution of large and small radius on the luminescence properties of Ca₂Ga Ta O₆:Cr³⁺double perovskite near-infrared phosphors was studied by cation substitution.By replacing the smaller radius Ga³⁺ions with larger radius Sc³⁺ions and In³⁺ions,the emission peaks are red-shifted from750 nm for Ca₂Ga Ta O₆:Cr³⁺to 797 nm for Ca₂Sc Ta O₆:Cr³⁺and 816 nm for Ca₂In Ta O₆:Cr³⁺.The introduction of large-radius cations destroys the structural stability of the original matrix,increases the fluorescence decay channel,and causes a decrease in luminescence intensity,which reduces the fluorescence lifetime from85.17μs of Ca₂Ga Ta O₆:Cr³⁺to 53.50μs of Ca₂Sc Ta O₆:Cr³⁺and 20.33μs of Ca₂In Ta O₆:Cr³⁺;The thermal stability performance was also weakened,and the thermal activation energyΔE values decreased from 0.36 e V to 0.33 e V and 0.29 e V.The Ga³⁺ions are replaced by Al³⁺ions with smaller ionic radius,and the emission peak position is blue-shifted from 750 nm of Ca₂Ga Ta O₆:Cr³⁺to 729 nm of Ca₂Al Ta O₆:Cr³⁺.The replacement of Ga³⁺ions by Al³⁺ions with a small radius improves the structural rigidity of the matrix,resulting in improved luminescence intensity and thermal stability.The emission spectrum intensity at 150°C is still 65%of that at room temperature,and the thermal activation energyΔE value is from 0.36e V of Ca₂Ga Ta O₆:0.02Cr³⁺raise to 0.41 e V.Comparing the emission spectrum of Ca₂Al Ta O₆:Cr³⁺near-infrared phosphor and the absorption spectrum of phytochrome,the emission spectrum of Ca₂Al Ta O₆:Cr³⁺can match the absorption spectrum of phytochrome P_FR,indicating that Ca₂Al Ta O₆:Cr³⁺is an ideal near-infrared phosphor for plant lighting.