Upconversion and Local Structure of Er<sup>3+</sup> Doped Aluminate Glasses

Abstract

The optical properties of Er3+ ions doped in aluminate glasses were investigated.(1) Among three intensity parameters obtained from absorption spectra by Judd-Ofelt theory, Ω2 and Ω4 showed a large value compared with those in other oxide glasses.(2) The multiphonon decay rates of the 4S3/2 and 4F9/2 levels were obtained from the radiative transition probabilities and concentration dependence of nonraiative decay rate. The values were nearly equal to those in a germanate glass. The energy gap dependence of the multiphonon decay rate was consistent with the phonon energy of this host, 800cm-1 obtained from the phonon sideband measurement.(3) The upconversion fluorescence at 550nm was observed with excitation at 650nm corresponding to the 4F9/2←4I15/2 absorption, for which the Ω4 value dominate the transition probability.(4) The profile of the excitation spectra of upconversion fluorescence by a tunable dye laser showed a deviation from that of the ground state absorption. This result indicates that the excited state absorption from the 4I13/2 level contributes the upconversion in the present glasses.