Upconversion and Local Structure of Er³⁺ 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 ⁴S_3/2 and ⁴F_9/2 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 ⁴F_9/2←⁴I_15/2 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 ⁴I_13/2 level contributes the upconversion in the present glasses.