First Pricinples Calculation And Experiment Study Of Infrared Luminescence For Multielement Co-doped Gadolinium Gallium Garnet

Er³⁺-doped near infrared?NIR?luminescence materials have wide range of applications in conmmunications,military,and environment detect,due to its unique optical properties asrised from Er³⁺optical transitions(⁴I_13/2?⁴I_15/2 transition around1533 nm).Designing crystal defects can improve the Er³⁺solubility in solid materials,thus iomproving their NIR luminescence intensity,lifetime,and efficiency.Recently,these NIR luminescent materials are activated by around 980 nm lasers,which have better properties.However,the wavelengths at around 980 nm are temperature dependent,which can lead to instability of light from NIR emission.Therefore,to design visible-light-activated Er³⁺-doped materials with strong NIR emission and a long lifetime is desirable.The challenge is that low absorption efficiency of visible light,which can be solved by doping to change the crystal defects.The first pricinples can reveals the internal structure defects and their optical behaviours of Er³⁺-doped crystal materials in depth.Combining the theory and experiment,the correlation of ctrystal defects and NIR luminescence properties can be studied.The object of the dissertation is set to calculate atomistic and electronic structures of Yb³⁺,Bi³⁺,Er³⁺co-doped Gd₃Ga₅O₁₂?GGG?by using density functional theory?DFT?to design a new NIR luminescence material with excellent luminescence properties.Combining theoretical and experimental results,the relationship between crystal defects and NIR luminescence properties has been obtained.Moreover,a low-cost Er³⁺-doped NIR luminescence material with excellent luminescence properties has been obtained from the nearest-neighbor mean-square relative displacement?MSRD??² of local Bi-O bonds,which established from XAFS measurement and temperature-dependent Raman spectra.Furthermore,a new magenitic sensitive NIR luminescence material obtained by analyzing the magnetic field effect on the NIR luminescence properties.By combining theoretical and experimental method,this dissertation provides an effective and reliable way to study the luminescence mechmism further,crystal defects,and magnetic field effect on NIR luminescence properties of rare-earth doped materials,and sheds new light on ways to develop high-NIR-luminescence materials and magnetic sensitive NIR luminescence materials in the future.The main results are as follows:1.Gd₃Ga₅O₁₂ and Fe³⁺-doped Gd₃Ga₅O₁₂ are the best host materials for the studies of NIR luminescence and magnetic sensitive NIR luminescence,respectively,by analyzing the atomic and electronic structures of Gd₃Ga_5-xFe_xO₁₂,which are calculated based on DFT+U.Band structure of GGG shows that GGG has a narrow conduction-and valence-band and small dispersity,which can improve the solubility of Er³⁺.In addtition,comparing with Gd₃Ga₅O₁₂,there is a redshift for Fe³⁺-doped Gd₃Ga₅O₁₂,and there is a s-p hybridization between accupied state Fe 3d and valence band of host,which can induce Zeeman splitting.2.Based on DFT+U,a novel,effective,visible-light-activated near infrared luminescent GGG:0.042Yb³⁺,0.084Er³⁺,0.042Bi³⁺system was designed by analyzing the atomic and electronic structures of GGG:Yb³⁺,Er³⁺,Bi³⁺.It exhibits strong emission intensity,high luminous efficiency?0.993?and a long lifetime?7.002 ms?,which are superior to the highest luminous efficiency and the longest lifetime reported in published papers.Together with experimental and theoretical results,the influence of defects on emission intensity has been analyzed.The locations of Yb³⁺,Er³⁺,and Bi³⁺are determined by X-ray absorption fine structure?XAFS?measurements,which are in agreement with the model constructed using first principles.3.The low-cost Er³⁺-doped NIR luminescence materials with excellent properties are more practical in practical applications.A correlation function between the Raman intensities and the nearest-neighbor MSRD?² of local Bi-O bonds is successfully established based on XAFS and temperature-dependent Raman spectra in the temperature range of 77-300 K in low-cost amorphous and crystalline Gd₃Ga₅O₁₂:0.02Yb³⁺,0.02Bi³⁺,0.02Er³⁺.The structural symmetries of Gd₃Ga₅O₁₂:0.02Yb³⁺,0.02Bi³⁺,0.02Er³⁺are described by using?² of local Bi-O bonds.More importantly,Gd₃Ga₅O₁₂:0.02Yb³⁺,0.02Bi³⁺,0.02Er³⁺is found to show excellent infrared?IR?emission properties due to changes in Bi-O bonds,and the IR emission intensities are found to depend on?²,by using temperature-dependent photoluminescence spectroscopy.The maximum emission intensity at 1533 nm is obtained when?²?0.003?at the lowest symmetry.4.The Zeeman splitting and f-f superexchange interaction of the f-f luminescence band(⁴I_13/2?⁴I_15/2)of Er³⁺in Gd₃Ga₄FeO₁₂:Yb³⁺,Er³⁺in high magnetic fields up to 38 T has been studied,and the conflict with Judd-Ofeld theory is properly explained based on DFT+U.There is redshifting and Zeeman splitting of the Er³⁺f-f band in high external magnetic fields,while the ferromagnetic Gd₃Ga₄FeO₁₂:Yb³⁺,Er³⁺splits at lower magnetic fields.Photoluminescence is found to be dependent on both temperature and magnetic field.Interestingly,the Zeeman splitting increases with increasing f-f superexchange interaction parameters based on density-functional theory?DFT?,and the intensity of the Er³⁺f-f transition increases with increasing field from 0 to 5 T,and then decreases above10 T,in conflict with the predictions of Judd-Ofelt theory.This behavior is a consequence of spd-f hybridizations between the occupied Er 4f orbitals and the valence states of Gd₃Ga₄FeO₁₂:Yb³⁺,Er³⁺,and it is independent of Fe³⁺concentration.