We investigated energy-transfer processes associated with clustered sites of Er<sup>3+</sup> ions in LiNbO<sub>3</sub> crystals leading to upconverted blue-green fluorescence and cross relaxation with the analyses of fluorescence transients measured by site-selective excitations. We found two clustered sites with distinct lifetimes of 3 and 16 μs at room temperature for the green fluorescing levels (<sup>4</sup>S<sub>3/2</sub>), which were much shorter than the lifetimes of isolated sites (27 μs) that are due to nonradiative energy-transfer processes. The green upconverted fluorescence originates from the energy transfer of one clustered site in the <sup>4</sup>I<sub>7/2</sub> levels, and/or of the other clustered site in the <sup>4</sup>I<sub>11/2</sub> levels. Our analyses verified that the fluorescence efficiencies of Er<sup>3+</sup> ions in the clustered sites are significantly decreased because of their interionic nonradiative energy transfers. Therefore, the formation of clustered sites in Er<sup>3+</sup>-doped LiNbO<sub>3</sub> crystals gives rise to deleterious effects on laser and amplifier applications.
© 2003 Optical Society of America
(160.3730) Materials : Lithium niobate
(300.2140) Spectroscopy : Emission
(300.6250) Spectroscopy : Spectroscopy, condensed matter
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
Jung Jin Ju, Myung-Hyun Lee, Myoungsik Cha, and Hyo Jin Seo, "Energy transfer in clustered sites of Er3+ ions in LiNbO3 crystals," J. Opt. Soc. Am. B 20, 1990-1995 (2003)