Absorption and luminescence phenomena in NaCl:Pb phosphors have been found to be rather complex. Melt-grown NaCl:Pb has an asymmetrical, 2730A-peaked absorption band. The variation of emission spectrum with wave-length of excitation within this band shows that it consists of two poorly resolved absorption bands, one peaking at 2730A and the other at 2900A. At low Pb concentrations, irradiation into the first of these causes a near-ultraviolet emission peaking at 3200A; irradiation into the second causes a visible emission peaking at about 4500A. At high Pb concentrations, irradiation into the first band gives a second near-ultraviolet emission band peaking at 3850A in addition to the one peaking at 3200A. Precipitated NaCl:Pb shows all the above phenomena, and in addition, has an excitation band peaking at 2600A, producing simultaneously a 3300A-peaked emission and a visible emission. The NaCl:Pb phosphors are unstable, deteriorating after a few days at room temperature and more rapidly at 130°. X-irradiation of these phosphors destroys the above absorption and emissions, and gives a print-out effect due apparently to the formation of colloidal Pb. The x-rayed material can be excited by near ultraviolet to give a red emission, peaking at about 6100A. Some suggestions concerning the interpretation of the above phenomena are given.
JAMES H. SCHULMAN, ROBERT J. GINTHER, and CLIFFORD C. KLICK, "Some Optical Properties of Lead-Activated Sodium Chloride Phosphors," J. Opt. Soc. Am. 40, 854-862 (1950)