We have studied the room temperature behavior of the Er<sup>3+</sup>:<sup>4</sup>S<sub>3/2</sub> fluorescence of three Er<sup>3+</sup>-doped crystals: Er<sup>3+</sup>:YLF with 30% and 8.5% doping and Er<sup>3+</sup>:BaYF doped at 20%. We studied the fluorescence by pumping with an 800-nm laser beam sinusoidally modulated in intensity in the range 10–1000 Hz, and we observed the presence of a second harmonic of modulation in the time evolution of the intensity of fluorescence. Second-harmonic intensity was also predicted by means of numerical integration of the rate equations that describe our system. Both experimental data and theoretical prediction show that the intensity reaches a maximum value at a modulation frequency that depends on the pump rate and on upconversion parameter α. This dependence allows us to obtain the value of α. To estimate this value we also measured the lifetimes of the various manifolds involved in the upconversion process.
© 2001 Optical Society of America
(190.7220) Nonlinear optics : Upconversion
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6250) Spectroscopy : Spectroscopy, condensed matter
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
(300.6420) Spectroscopy : Spectroscopy, nonlinear
Luigi Palatella, Alberto Di Lieto, Paolo Minguzzi, Alessandra Toncelli, and Mauro Tonelli, "Er3+-doped crystals: frequency analysis of nonlinear energy transfer," J. Opt. Soc. Am. B 18, 1711-1717 (2001)