Infrared-to-visible upconversion inLaCl3:1%Er3+: Energy-level and line-strength calculations

Abstract

Single crystals of ${\mathrm{LaCl}}_{3}{:1%\mathrm{}\mathrm{Er}}^{3+}$ were grown by the Bridgman technique. ${\mathrm{Er}}^{3+}$ substitutes for ${\mathrm{La}}^{3+}$ and has a site symmetry of ${C}_{3h}$ in ${\mathrm{LaCl}}_{3}.$ Seventy-three energy levels of ${\mathrm{Er}}^{3+}$ were determined up to $45000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ from absorption, excitation, and luminescence spectra measured over the temperature range 4.2--293 K. A correlated crystal-field analysis was done by fitting 16 atomic, four crystal-field, and one correlated crystal-field parameters to the experimental Stark levels. The fit is excellent with a standard deviation of $9.0{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}.$ On the basis of the wave functions thus obtained the oscillator strengths for the transitions from the ${}^{4}{I}_{15/2}(1)$ ground state to all the levels up to $45000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were calculated by fitting seven complex ${A}_{t,p}^{\ensuremath{\lambda}}$ intensity parameters to 47 observed oscillator strengths. The intensity distribution among the crystal-field components was then calculated for the inter-excited-state transition ${}^{4}{I}_{11/2}{\ensuremath{\rightarrow}}^{4}{F}_{7/2}$ which plays an important role in an excited-state-absorption upconversion process.