Dynamics of the IR-to-blue wavelength upconversion inPr3+-doped yttrium aluminum garnet andLiYF4crystals

Abstract

The infrared-to-blue upconversion in ${\mathrm{Pr}}^{3+}$-doped yttrium aluminum garnet and yttrium lithium fluoride crystals has been studied at temperatures between 4.4 and 300 K for different activator concentrations. The excitation spectra and decay-time measurements indicated the sequential absorption of two photons between levels of the 4${\mathit{f}}^2$ electronic configuration. The first photon is absorbed nonresonantly by a weak phonon band associated with the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{H}}_4$ ${\to }^1$ ${\mathit{G}}_4$ transition; the second resonant absorption step is from the ${}_{}{}^1{}_{}{}^{}$ ${\mathit{G}}_4$(1) to one of the ${}_{}{}^1{}_{}{}^{}$ ${\mathit{I}}_6$ levels that relax to the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ state. Transitions from the excited ${}_{}{}^1{}_{}{}^{}$ ${\mathit{G}}_4$ state obeyed the spin and point symmetry selection rules for electric-dipole transitions. Excited-state-absorption spectra revealed structure not observed in one photon absorption and excitation spectra.