Phonon Mode and Electron-phonon Coupling Strengths Controlling the Fluorescence Efficiency of Dy~(3+)-doped Selenide Glasses

Pure and Dy~(3+)-doped Ge30Ga5Se65 and 0.9Ge_(30)Ga_5Se_(65)+0.1CsBr glasses were prepared by conventional melt-quenching method.The intensity parameters,spontaneous emission probability and branching ratio of Dy~(3+)ions in Ge_(30)Ga_5Se_(65)+CsBr glass were calculated by Judd-Ofelt theory.The lifetime of ~6H_(11/2)level at temperatures from 20K to 300K were measured to investigate the temperature dependence of multiphonon relaxation(MPR)rates.The influence of the local phonon mode and electron-phonon(e-p)coupling strength on the 1.72μm fluorescence efficiency of Dy~(3+)-doped selenide glasses was investigated.The frequency of the phonon vibration is changed to 268cm~(-1)due to the formation of Ga-Br bonds with the addition of CsBr to selenide glasses.The values of e-p coupling strengths in Ge_(30)Ga_5Se_(65)and 0.9Ge30Ga5Se65+0.1CsBr glasses are 0.456 and 0.048,respectively.It is clear that the e-p coupling strengths decrease considerably with the addition of CsBr to Ge_(30)Ga_5Se_(65) glass.This reduced e-p coupling together with a large change in the local phonon mode result in the change of the MPR rate.