液氦温度(4.2K)下LaOBr:Ce3+,Tb3+粉末的电子顺磁共振研究

本文研究了LaOBr:Ce+3,Tb3+粉末在液氦温度(4.2K)下的电子顺磁共振,并且进行了晶体场理论计算,理论与实验结果符合得较好,这表明Ce,Tb离子取代了基质中La离子形成发光中心。

EPR INVESTIGATION OF LaOBr:Ce3+,Tb3+ POWDER AT LIQUID HELIUM TEMPERATURE(4.2K)

We have investigated the EPR spectra of LaOBr:Ce3+,Tb3+ powder at liquid helium temperature(4.2K).The EPR signals of three samples with differential concentrations of Ce3+and Tb3+have been obtained on the X-band at 4.2K.The measured results are as follows:ion sample1 2.3Ce3+ g=2.440 g=2.457Tb3+g=3.110 g=3.125The EPR spectra of LaOBr:Ce, Tb powder are computed according to crystalline field theory.The crystalline field Hamiltonian of LaOBr:Ce3+ Tb3+ crystal is computed by means of point charge model.Using Stevens’“Operator Equivalents”method,we have obtained the crystalline field Hamiltonian operator:where Amn=-|e|γnm const are known as the “crystal field parameters”, and γnm are coefficients which are related to the crystal structure.The particular form of for LaOBr:Ce3+Tb3+is: Using the Hamiltonian operator, we have computed the energy level splitting of Ce3+ and Tb3+ ions in LaOBr crystal by perturbation theory at representations |LzSz| and |JJz| respectively.On this basis the values of g-factor of Ce3+ and Tb3+ ions are obtained:g=2.487 for Ce3+iong=3 for Tb3+ ionAccording to the theory of Ibers ’et al., through analyzing the line shape of powder EPR spectra.It is verified that the factor of crystal is almost equal to the that of LaOBr:Ce3+Tb3+powder.The calculated result agrees very well with the experimental result.It is thus affirmed that the dopant Ce3+ and Tb3+ions substitute La3+ ions in host material and form luminescence centers.