Luminescence, excited in some carefully purified crystalline barium and radium compounds by alpha-, beta-, and gamma-rays has been examined. It is found that these compounds show a faint luminescence at ordinary room temperatures. When the compounds are heated to various temperatures and then cooled, they show a continuous increase in luminescence with increase of temperature of heat treatment until a maximum is reached. Heat treating at higher temperatures diminishes the brightness. The temperature of maximum brightness is not directly related to the melting point of the individual compounds. The maximum brightness in some cases was several hundred times the initial brightness of unheated crystals. No abrupt changes in intensity of luminescence, such as might be due to changes in crystalline form, were detected. The bearing of these experiments on the modern theories of luminescence in crystalline solids is discussed.