Effect of cross relaxation on the 1470 and 1800 nm emissions in Tm³⁺:TeO₂–CdCl₂ glass

We have used spectroscopic methods to investigate the effect of cross relaxation on the 1470 and 1800 nm emissions in Tm³⁺:TeO₂–CdCl₂ glass for Tm³⁺ ion concentrations of 0.05, 0.1, 0.25, 0.5 and 1.0 mol%. The emission spectra obtained under 800 nm excitation reveal the existence of energy transfer via cross relaxation among the Tm³⁺ ions. As a result, as the thulium concentration is increased, the strength of the 1470 nm emission is found to decrease in relation to that of the 1800 nm emission. The analysis of the time evolution of the ³F₄ emission due to the transition further shows that the electronic mechanism responsible for the ion–ion interaction can be identified as an electric dipole–dipole energy transfer process and occurs in the diffusion-limited relaxation regime. The average critical distance parameter which provides a measure for the strength of cross relaxation was further determined to be 17.9 Å.