Dynamics of the IR-to-blue wavelength upconversion in Pr3+-doped yttrium aluminum garnet and LiYF4 crystals.

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}$${\mathit{H}}_{4}$${\ensuremath{\rightarrow}}^{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.