Research On Impurity Levels Induced By Lanthanide Ions And 3d Transition Metal Ions In Luminescent Materials

Impurity levels induced by doping ions in the matrix,affect the properties of luminescent materials.Lanthanide ions and 3d transition metal ions,as common activators,are widely used in luminescent materials.It is of great significance to study the energy level of impurities formed by them.Therefore,this paper explores the impurity level positions of lanthanide ions and some 3d transition metal ions,respectively.First,Ca Al Ga O₄:Ln³⁺（Ln=Eu,Tb,Sm,Dy）and Ca Al Ga O₄:Ln³⁺,RE³⁺（Ln=Eu,RE=Tb,Sm）phosphors are synthesized by solid state reaction method and thermoluminescence properties are investigated in the third chapter.Monitored at 614nm,the excitation spectrum of Ca Al Ga O₄:Eu³⁺has performed one broad band ranging from230-300nm belongs to charge transfer band（CTB）of O^2-→Eu³⁺with maximum at 264nm.By using chemical shift model,combining the charge transfer of Eu³⁺and the estimated value U（6）,we constructs the vacuum referred binding energy（VRBE）of 4f ground state of divalent and trivalent lanthanide ions in the Ca Al Ga O₄.On this basis,through the study of thermoluminescence,we found that Sm³⁺is seen as electron-trap,while Tb³⁺and Pr³⁺act as hole-trapping centers.Finally,there is a consistency between VRBE and the trap depth caused by lanthanide doped.The persistence of Sr La Al O₄:Tb³⁺is explained by this relation.In the fourth chapter,the impurity level positions caused by 3d transition metal ions in wide-bandgap compounds are studied,and the change rules of these impurity levels with the change of matrix are explored.By collecting CT values of Mn⁴⁺,Cr³⁺and Fe³⁺in octahedrons from previous published papers,the energy level positions of Mn^4+/3+,Cr^3+/2+and Fe^3+/2+in different matrices are obtained.It is found that there is a linear variation between the positions of these energy levels and the valence band maximum（VBM）positions.A new method for obtaining impurity energy levels of 3d transition metal ions is proposed and explained by molecular orbital theory.Meanwhile,Ca Al₂O₄:TM(TM=Fe³⁺,Ni³⁺,Ti⁴⁺,Cu²⁺)is synthesized experimentally.By measuring the absorption of these samples,the impurity energy level positions formed by these ions in the tetrahedron are obtained.Surprisingly,the sample Ca Al₂O₄:Cu²⁺emitted blue-green light at 240nm excitation,providing a new research direction for the exploration of Cu²⁺-doped phoshpors.For Mn⁴⁺luminescent materials,based on first principles calculation in the fifth chapter,the electronic structures of Mn⁴⁺doped Y₃Al₅O₁₂（YAG）,K₂Ti F₆（KTF）and Zn Ti F₆?6H₂O（ZTF）are obtained.By comparing the energy difference between the impurity level positions of Mn⁴⁺and VBM,the mechanism of hole-type quenching is proposed and discussed.For the extrinsic impurity ion,if the impurity ion brings the hole type defect,it can stabilize Mn ion at+4 valence and enhance the emission intensity of Mn⁴⁺doped phosphors.Therefore,this mechanism can further explain the properties of Mn⁴⁺doped luminescent materials.And researchers can also use this mechanism to design Mn⁴⁺doped phosphors by adjusting the chemical composition of the matrix.