Quenching of the total luminescence ofHo3+inHoLiF4crystals

The luminescent-channel efficiency for ${\mathrm{Ho}}^{3+}$ ions in ${\mathrm{HoLiF}}_4$ crystals was measured and compared with the case of ${\mathrm{Ho}}^{3+}$ as a low-concentration dopant (1.71%) in crystals of ${\mathrm{YLiF}}_4$. The ${}_{}{}^5{}_{}{}^{}$ ${\mathit{S}}_2$ ${\to }^5$ ${\mathit{I}}_7$, ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_8$ luminescent transitions are strongly quenched by two possible cross-relaxation processes: one with almost zero mismatch energy, favoring the population of the ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_5$, ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_6$, and ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_7$ levels, and the other, a laser transition ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_7$ ${\to }^5$ ${\mathit{I}}_8$ in the mid-infrared region. Also seen was a strong decrease of the total ${\mathrm{Ho}}^{3+}$ luminescence by approximately 6.6 times in ${\mathrm{HoLiF}}_4$ crystals from 10 to 300 K. This quenching effect was attributed to an energy transfer from the ${\mathrm{Ho}}^{3+}$ excited ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_6$ and ${}_{}{}^5{}_{}{}^{}$ ${\mathit{I}}_7$ levels to traps present in the crystal.