Visible and infrared up-conversion emission in Er3+-doped fluorochlorozirconate glasses under 1550 nm and 980 nm excitations

Upconversion (UC) and photoluminescence (PL) measurements were carried out on trivalent erbium (Er³⁺) doped fluorochlorozirconate (FCZ) glasses. The experiments show that neither PL spectra nor PL relaxation times depend on Er³⁺ concentration up to 2 at.%, indicating the absence of clusterization and collective effects. Radiation diffusion was also excluded based on the PL decay lifetime being experimentally the same in powder and bulk samples. Additionally, FCZ:Er³⁺ shows an efficient up-conversion in visible and IR regions under 1550 nm or 980 nm pumping. The intensity of up-converted PL bands versus pumping intensity (G) behavior follows PL ∝ Gⁿ with n varying from 1 to 3 depending on the PL band and pump wavelength and intensity. The observed dependences and variation of n may be interpreted by a model of linear rate equations for seven lower manifolds, approximated by six monolevels. The validity of this approximation is supported by the application of the McCumber theory to the shapes of PL and optical absorption spectra. The present model for the experimental data was also supplemented by using Judd-Ofelt parameters obtained from the absorption spectra on the same set of glasses. It should be emphasized that the model developed in this work provides a self-consistent interpretation of the upconversion experiments at 1550 and 980 nm pumping reported herein.