Abstract:
A series of fluoride glass samples of the composition ZBLAN:1%Er$^{3+}$, ZBLAN:1%Ho$^{3+}$, ZBLAN:1%Er$^{3+}$+X%Ho$^{3+}$ (X = 0.25, 0.5, 1 mol.%) is synthesized. Based on the transmission spectra of the compounds ZBLAN:1%Ho$^{3+}$ and ZBLAN:1%Er$^{3+}$, the Judd–Ofelt intensity parameters for Ho$^{3+}$ and Er$^{3+}$ ions in synthesized samples are determined. Up-conversion luminescence of ZBLAN:Er$^{3+}$/Ho$^{3+}$ glass under excitation Tm$^{3+}$:YAP laser radiation with a wavelength of 1.94 $\mu$m is investigated. The up-conversion luminescence spectra of the visible range exhibit bands in the regions of 545 and 655 nm. The highest intensity was observed for the red lines at a wavelength of 655 nm, which correspond to the transitions ${}^4F_{9/2}\to {}^4I_{15/2}$ of Er$^{3+}$ ions and ${}^5F_5\to{}^5I_8$ of Ho$^{3+}$ ions. The threshold power density of radiation visualization of Tm$^{3+}$:YAP laser decreased with increasing concentration of Ho$^{3+}$ ions and was 30 W/cm$^2$ in the ZBLAN:1%Er$^{3+}$+1%Ho$^{3+}$ sample.
Keywords:Judd–Ofelt theory, up-conversion luminescence, visualization of IR radiation, fluoride glass, rare-earth elements.
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