Abstract

Studies have been made of the effects of non-radiative loss of the energy absorbed by phosphors which occur when excitation frees electrons from luminescence centers in the phosphors so that they move freely in the matrix crystal. Such non-radiative losses also occur at elevated temperatures when the thermal energy of the phosphor is sufficient to free electrons from the excited states of the emission centers. These processes give rise to a non-linear variation of the luminescence intensity with the intensity of excitation, as observed by previous workers. In addition to more exhaustive studies of this non-linear behavior of the luminescence, we have made studies of the semi-conduction, photo-conduction and thermoelectric effects in phosphors at temperatures where the non-radiative processes are present. These electrical measurements show that at elevated temperatures phosphors behave as excess semi-conductors, that is, the observed current is due mainly to electrons and not to positive hole motion, as assumed by some previous workers. The investigations provide a qualitative explanation of the low efficiency of excitation of phosphors by particles or high energy quanta. They show that for excitation by ultraviolet light of wave-length greater than that of the fundamental absorption edge of the phosphor matrix (zinc sulphide phosphors), the electrons excited do not leave the neighborhood of the emission centers and only give rise to transient photoconductivity effects having the nature of displacement currents.

© 1949 Optical Society of America

The Relation between Efficiency and Exciting Intensity for Zinc-Sulphide Phosphors

H. A. Klasens, W. Ramsden, and Chow Quantie
J. Opt. Soc. Am. 38(1) 60-65 (1948)

Theory of the Luminescence of Sulfide Phosphors

Shepard Roberts and Ferd E. Williams
J. Opt. Soc. Am. 40(8) 516-520 (1950)

Review of the Interpretations of Luminescence Phenomena*

Ferd E. Williams
J. Opt. Soc. Am. 39(8) 648-654 (1949)

The Optical and Electrical Properties of Zinc Silicate Phosphors

Elemér Nagy
J. Opt. Soc. Am. 39(1) 42-49 (1949)

Optical Properties of Calcium Silicate Phosphors

Frank J. Studer and Gorton R. Fonda
J. Opt. Soc. Am. 39(8) 655-660 (1949)