First Pricinples Calculation and Experiment Study of Infrared Luminescence for Multielement Co-doped Gadolinium Gallium Garnet

Author:Tong Li Ping

Supervisor:fan tong xiang


Degree Year:2018





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(4I13/2→4I15/2 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)σ2 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 Gd3Ga5-xFexO12,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 MSRDσ2 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 usingσ2 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 onσ2,by using temperature-dependent photoluminescence spectroscopy.The maximum emission intensity at 1533 nm is obtained whenσ2~0.003?at the lowest symmetry.4.The Zeeman splitting and f-f superexchange interaction of the f-f luminescence band(4I13/2→4I15/2)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.