The effect of K+ ions on GdTaO4:Eu3+ thin-film phosphors was investigated in order to improve their luminescent properties. The GdTaO4:Euo(0.1), K-x thin films were synthesized by sol-gel process, and characterized through measuring their microstructure and luminescence. The results indicated that photoluminescence (PL) intensity of GdTaO4:Eu3+ film was improved remarkably by K doping. There were two maxima in the curve of PL intensity against K+ dopant concentration, where one was improved up to 2.1 times at x = 0.001 and the other was enhanced up to 2.7 times at x = 0.05. The first maximum was regarded as the alteration of the local environment surrounding the Eu3+ activator by incorporation of K+ ions, and the second maximum was due to the flux effect. Additionally, the luminescence increased with the increase of firing temperature from 800 degrees C to 1200 degrees C. (c) 2006 Elsevier B.V. All rights reserved.