The temperature dependence of photoluminescence (PL) spectra of Er-Tm codoped calcium boroaluminate (CABAL) glasses with different dopant concentrations was investigated under 15–298 K, by pumping at 795 nm. The intensities of three band emissions located at 1.46, 1.53, and 1.80 μm decreased monotonically when increasing the temperature from at lower concentrations. However, the emissions peaked at 1.80 μm increase with the increasing temperature at higher concentrations. This was attributed to the increasing of cross relaxation (CR) resulting from the high doping concentration of Tm ions. This was evidenced by the much shorter fluorescence lifetime of 56 μs for the emission due to transition for the CABAL glass codoped with 2.00 mol.% , in comparison with 185 μs for that of 0.2 mol.% . The energy transfer (ET) and CR processes between and ions have been discussed at different doping concentrations and operating temperatures. The nonexponential character of the decays of and with the increasing concentration indicated the occurring of a dipole-dipole quenching processes in the framework of a diffusion-limited regime. The average critical distances of CR between ions and ET between and ions were approximately 1 nm.
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