An efficient ultratine orange-emitting SnO2:Eu3+ phosphor for vacuum fluorescent displays was synthesized by the combustion method. In this study, by varying the molar ratio of citric acid to HNO3 as a process parameter, the influence of HNO3 on characteristics of the phosphor was investigated. From combustion reactions fine and small-sized powders were obtained, which could not be achieved by a solid-state reaction. The SnO2: Eu3+ synthesized with varying the molar ratio of citric acid to HNO3 showed significantly different characteristics by varying the ratio. When the atmosphere inside the vessel used during the combustion reaction with HNO3 was close to a stoichiometric combustion reaction condition, the crystallite size became smaller than in other cases and crystallinity was improved so that the cathodoluminescence (CL) intensity of the SnO2:Eu3+ phosphor was improved up to about 50%. From these results, it is understood that the CL intensity of the combustion-synthesized SnO2:Eu3+ phosphor depends significantly on the reaction atmosphere which is controlled by the molar ratio of fuel to oxidizer. (c) 2005 The Electrochemical Society. [DOI: 10. 1149/1.1855873] All rights reserved.