Methods of manufacturing a light-activated powder are provided which provide solid-state generation and release of chlorine dioxide without detectable amounts of any toxic by-products such as chlorine gas, chlorites, or chlorates. The powder need not be exposed to moisture, relative humidity, or an acid before or during exposure of the powder to visible light to generate the gas. The powder can also be prepared under conditions that minimize or prevent decomposition or oxidation of sodium chlorite or premature light activation of the powder during the manufacturing process to maximize its activity.