Electroluminescence with Nonsinusoidal Fields

Abstract

Electric fields in the form of square or rectangular waves, saw‐tooth waves, and exponential waves were applied to an electroluminescent phosphor. The light output contained green and blue luminescence bands, which were examined separately by means of filters, a photomultiplier, and an oscilloscope. Square wave fields produce luminescence peaks whenever the field is changing, followed by a decline in luminescence when the field is steady. Peak heights increase proportionally to about the fourth power of the field strength. They decrease with increasing frequency for the green band, while for the blue band they first increase up to about 2000 cps and then decrease. The decay obeys power laws with different exponents before and after a critical time of about 0.7 msec. A rectangular field pulse of greater duration than the critical time produces, in the green band, peaks of equal total intensity at the field reversals; in the blue band, the same excitation produces peaks with equal changes in intensity. Other field shapes produce peaks of luminescence whose heights and shapes depend on field shape and duration of the steady field before it is changed. Additional peaks in the green band appear whenever the field begins to decrease.Observations are interpreted by using the following assumptions: excitation is due to collision processes of accelerated electrons; green luminescence involves transitions to the conduction band and to traps; blue luminescence is caused by transitions within a luminescence center; the effective field changes in time because of the development of polarization charges. Additional peaks in the green band are due to recombination processes of the polarization charges.