Excited-state absorption in ${\mathrm{BaY}}_2$${\mathrm{F}}_8$:${\mathrm{Nd}}^{3+}$

Upconversion pumping with yellow cw and pulsed dye lasers was used to produce uv and blue light arising from deexcitation of the ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{3/2}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ states of ${\mathrm{Nd}}^{3+}$ ions in ${\mathrm{BaY}}_2$${\mathrm{F}}_8$:${\mathrm{Nd}}^{3+}$. Upconversion excitation occurs via sequential two-photon absorption, which was probed by the anti-Stokes emission dynamics and by a two-color laser experiment. An analysis of the steady-state populations as a function of pumping rates ${\mathit{R}}_1$ and ${\mathit{R}}_2$ for the two-step excitation is developed. When the excitation frequency is resonant with the ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{3/2}$${\to }^4$${\mathit{D}}_{3/2}$ excited-state absorption transition, the power dependence of the anti-Stokes fluorescence intensity, plotted on a logarithmic scale, shows a straight line with a slope of 1.8. This behavior is explained quite well by the model for a mean-excitation-power regime where the second step is 4 orders of magnitude more efficient than the ground-state absorption.