* Corresponding author. Tel.: #48 56 210 65; fax: #48 56 253 97; e-mail: koepke@phys.uni.torun.pl. Journal of Luminescence 78 (1998) 135 — 146 Excited state absorption in Cr-doped gahnite glass ceramics Czes"aw Koepke*, Krzysztof Wis´niewski, Marek Grinberg, David L. Russell, Keith Holliday, George H. Beall  Institute of Physics, Nicholas Copernicus University, Grudzia 9 dzka 5/7, 87-100 Torun & , Poland  Institute of Experimental Physics, University of Gdan & sk, Wita Stwosza 57, 80-952 Gdan & sk, Poland  Department of Physics and Applied Physics, Strathclyde University, Colville Bldg, Glasgow G1 1XN, UK  Corning Incorporated, Corning, NY 14831, USA Received 19 June 1997; received in revised form 7 October 1997; accepted 27 October 1997 Abstract We report on the excited state fluorescence and absorption characteristics of chromium-doped gahnite glass ceramic. The material is characterized by a very structured and wide emission spectrum despite its lowest excited state being the doublet E  , usually associated with very weak electron—phonon coupling. Excited state absorption is principally from the doublet E  to three higher-energy doublets though an additional contribution due to the gahnite glass ceramic host is also present during UV excitation. The chromium excited state absorption has been extracted from the overall spectrum. Utilizing data from the emission, absorption and excitation spectra, the configuration coordinate diagram describing octahedrally coordinated Cr ions in the gahnite glass ceramic has been produced. From this diagram the expected excited state absorption spectrum, including the influence of bleaching, has been modelled and a comparison made with experimental data.  1998 Published by Elsevier Science B.V. All rights reserved. PACS: 78.20; 78.20.Dj; 42.70.Ce; 78.55.!m; 78.55.Hx Keywords: Solid state spectroscopy; Excited state absorption; Cr; Inorganic glasses 1. Introduction A chromium-doped material was the first laser gain medium and many others have been found and commercially exploited during the following four decades. The basic spectroscopy of these ma- terials is well developed though some aspects still remain unclear. These mainly concern materials with site-to-site distributions of the crystal field parameters, manifested in the inhomogeneous broadening of the radiative transitions. Especially interesting are chromium-doped materials based on glass or glass ceramics due to their potentially lower production costs relative to crystals. Gahnite glass ceramics are particularly interesting hosts. This material is originally a glass but, after specific thermal treatment, transforms into a glass ceramic, a state that involves crystalline order on a local scale but an amorphous structure over a longer range. The name “gahnite” originates in min- eralogy and refers to materials with a composition based on ZnAl  O  . Gahnite glass ceramics seem to 0022-2313/98/$19.00  1998 Published by Elsevier Science B.V. All rights reserved PII S0022-2313(97)00307-4