Thermophosphorescence of glass colored violet by previous exposure to radium emanation. (1) Visible light emitted by the glass when heated to temperatures around 115° to 255° C was measured with a polarization photometer, using radium luminous paint as comparison source. The total quantity of light emitted by equal areas of similarly radiated glass of the same thickness was found by integration of the curves to be constant, independent of the temperature or rate of light emission. The rate of decrease of light intensity at constant temperature approximately fits the equation for second order chemical reaction dx/dt=k(a-x)2. The values of the velocity constant k increase with temperature in accordance with the van’t Hoff equation log K=C-a/T. The temperature coefficient is somewhat lower than that characteristic of chemical reaction but higher than for most purely physical reactions. (2) Heat radiation. Measurements made with a Coblentz silver-bismuth thermopile failed to detect any increased heat radiation accomanying the luminescence.
R. E. NYSWANDER and S. C. LIND, "MEASUREMENTS OF THERMOPHOSPHORESCENCE OF GLASS PRODUCED BY RADIUM RADIATION," J. Opt. Soc. Am. 13, 651-660 (1926)