Abstract
Crystals of doped with exhibit a strong orange luminescence under near-infrared excitation at 10 K. The broad emission band extending from 17 200 to 13 000 is identified as a transition on Of the two inequivalent sites identified by site-selective high-resolution spectroscopy, only one is able to induce efficient upconversion. Excitation with 10-ns pulses indicates that no energy transfer is involved, and the upconversion process consists of a sequence of ground-state absorption and excited-state absorption steps. One- and two-color excitation spectra confirm the occurrence of these two steps. The efficiency of the upconversion process at 10 K and for an excitation power of 200 mW focused by a 53-mm lens is 2 percent. An upconversion mechanism based on exchange interactions between the and ions is proposed to account for the observed behavior.
- Received 19 September 2000
DOI:https://doi.org/10.1103/PhysRevB.63.165102
©2001 American Physical Society