Chromium centers in LiNbO3 revisited

In this paper we present novel spectroscopic data clarifying the nature of the dominant Cr3+ centers in LiNbO3. In the past, the Cr3+ centers in LiNbO3 have been the subject of intense debate, which was partly caused by the intrinsic Li+ deficit present in the available congruent samples, which leads to highly complex emission spectra. Recently, stoichiometric samples have become available which show a greatly reduced number of emission lines of defect-related high-field sites in the so-called R-line region. We have carried out extensive absorption, emission, resonant photoexcitation, and time-resolved measurements between 2 K and room temperature to unravel the nature of the dominant Cr3+ sites in LiNbO3. From these studies we conclude that the dominant luminescent center is a Cr3+ ion at a low-field site in both stoichiometric and congruent samples. (C) 1999 Elsevier Science B.V. All rights reserved.