We present a comprehensive spectroscopic study of the possible room-temperature green laser transition <sup>2</sup>H<sub>9/2</sub>→<sup>4</sup>I<sub>13/2</sub> in Ba<sub>2</sub>YCl<sub>7</sub>:3%Er<sup>3+</sup>. Because of the low phonon energies, 270 cm<sup>−1</sup> in Ba<sub>2</sub>YCl<sub>7</sub>, the otherwise multiphonon-quenched <sup>4</sup>I<sub>9/2</sub> and <sup>2</sup>H<sub>9/2</sub> levels are metastable and can serve as intermediate pump and upper laser levels, respectively, for a green upconversion laser excited at 800 nm. Polarized spectra of ground-state and excited-state absorption at 800 nm and of emission at 560 nm are measured, and the corresponding absorption and emission cross sections are derived. Luminescence-decay measurements provide lifetime data. Despite the large number of metastable levels of Er<sup>3+</sup> in a low-phonon host material, luminescence spectra and intensity-versus-power measurements reveal that the energy dissipation into levels other than those required for the operation of the laser transition (i.e., <sup>4</sup>I<sub>15/2</sub>→<sup>4</sup>I<sub>9/2</sub>→<sup>2</sup>H<sub>9/2</sub>→<sup>4</sup>I<sub>13/2</sub>) is small at low dopant concentrations. At higher concentrations, an energy-transfer upconversion process populates the lower laser level and counteracts inversion. The theoretical pump threshold of the proposed upconversion-laser transition under cw and pulsed excitation is derived.
© 2000 Optical Society of America
(160.4760) Materials : Optical properties
(160.5690) Materials : Rare-earth-doped materials
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
(300.6360) Spectroscopy : Spectroscopy, laser
R. Burlot-Loison, M. Pollnau, K. Krämer, P. Egger, J. Hulliger, and H. U. Güdel, "Laser-relevant spectroscopy and upconversion mechanisms of Er3+ in Ba2YCl7 pumped at 800 nm," J. Opt. Soc. Am. B 17, 2055-2067 (2000)