Design,synthesis And Luminescence Mechanism Of Mn⁴⁺ Doped Double Perovskite Far-red Light Emitting Phosphor

In recent years,Mn⁴⁺doped tungstate phosphor with double perovskite structure has potential application in plant growth due to its low cost,easy synthesis,and excellent optical properties.However,Mn⁴⁺doped tungstate phosphors face a series of challenges,including low luminous efficiency and poor thermal stability,which have severely restricted their practical applications.Therefore,the research aims is to improve the luminescence properties and stability of tungstate phosphors by forming solid solutions,adding sensitizers,and optimizing synthesis methods for better use in plant growth.1.A new type of double perovskite Ca_2-2xNa_xLa_xMg WO₆:0.5%Mn⁴⁺far-red light emitting phosphors were designed in this paper.The transition from no light to strong far-red light emission is realized by replacing―2Ca²⁺‖with―Na⁺+La³⁺‖.This replacement adjusts the symmetry of the crystal structure of Ca₂Mg WO₆,thereby breaking the forbidden transition of Mn⁴⁺luminescence in Ca₂Mg WO₆.In-depth analyses of XRD,infrared,Raman,XPS prove the continuous solid solution transformation from Ca₂Mg WO₆ to Na La Mg WO₆ and the change of luminescence properties.Under the excitation of 353 nm,the optimal phosphor Ca_1.0Na_0.5La_0.5Mg WO₆:0.5%Mn⁴⁺(abbreviated as CNLMW:Mn⁴⁺)exhibited far-infrared emission in the range of 600-800nm centered at 700 nm.The thermal stability and quantum efficiency of the CNLMW:Mn⁴⁺phosphor are increased by 29.77%and 29.72%respectively,compared to those of the original Na La Mg WO₆:Mn⁴⁺in room temperature.In addition,there is a broad spectrum overlap between the emission band of the phosphor CNLMW:Mn⁴⁺and the absorption spectrum of the plant pigment P_FR,which indicates that the phosphor has potential value in promoting plant growth.2.Novel Er³⁺and Mn⁴⁺ions co-doped Ca_1.0Na_0.5La_0.5Mg WO₆color-tunable phosphors were synthesized by high temperature solid phase method.The Er³⁺and Mn⁴⁺activated Ca_1.0Na_0.5La_0.5Mg WO₆phosphors show intense green（528 nm）and red（700 nm）emission,corresponding to the ²H_11/2→⁴I_15/2,⁴S_3/2→⁴I_15/2transition of Er³⁺and the²E_g→⁴A_2g transition of Mn⁴⁺,respectively.Moreover,the emitting lights of Ca_1.0Na_0.5La_0.5Mg WO₆:Er³⁺,Mn⁴⁺phosphors changed from green to red by increasing concentration ratio of Er³⁺/Mn⁴⁺.Emission spectra combined with fluorescence decay curves proved the energy transfer between Er³⁺-Mn⁴⁺.The type of energy transfer belongs to the dipole-dipole interaction,and the energy transfer efficiency is as high as40.75%.3.A series of Ca_1.0Na_0.5La_0.5Mg WO₆:0.5%Mn⁴⁺phosphors were synthesized by microwave heating method.The microwave heating method has the characteristics of energy saving,high efficiency and rapidity,and the prepared samples are relatively loose compared with the traditional high-temperature solid-phase reaction.This chapter explores the influence of microwave heating temperature and time on the luminescence performance of phosphors.The experimental results show that the luminous intensity of phosphors synthesized by microwave heating are increased by 70.5%(λ_ex=353 nm)and 73.6%(λ_ex=470 nm)compared to high-temperature solid-phase method.In addition,we also compared the properties of phosphors prepared by wet ball milling and grinding methods.