Structure and Location of Electroluminescent Light Emission within ZnS∕Cu ACEL Powder Phosphor Particles

Abstract

Localized electroluminescent ͑EL͒ light emissions have been imaged in ZnS/Cu ac EL ͑ACEL͒ powder phosphor particles embedded under high-refractive index glass. Undistorted well-resolved images recorded at a series of depths from base to apex of individual particles show that in sharp focus the EL emissions are always small ͑1-2 m͒ bright dots, often arranged along short straight lines. Comparison with backlit images shows that EL emission sites are near the phosphor surface. Image series recorded over a range of excitation voltages show that this surface luminous structure is unaltered under increased field strength, but more sites become active. There is no evidence for luminous comets within the particles. The data, clearly showing alternation of EL emission from side to side of the particles on opposite-polarity ac half-cycles, continue to support a mechanistic model in which electrons and holes are separated during one polarity and then undergo radiative recombination when that polarity is reversed on the succeeding half cycle. The small, surface-positioned emissive spots indicate that this charge-carrier separation does not occur at long acicular internal structures but rather at short Cu 2 S structures active only at the ZnS surface.

Structure and Morphology of ACEL ZnS:Cu,Cl Phosphor Powder Etched by Hydrochloric Acid

“…This suggests that each exposed surface supports ACEL as a particle is progressively etched. This is consistent with ACEL light emission that is due to electron-hole recombination at the surface of the phosphor particles, 8 but it seems to indicate that charge recombination, giving rise to light emission, can also occur at surfaces that are exposed by acid etching. Some morphological changes occur after etching for longer periods of time, as can be seen by comparing Fig.…”

AC electroluminescent lamps: shedding some light on their mysteries

“…Increasing the voltage enhances hole transport and causes the light emitting zones to be spaced further apart, and thus increases the observed pulse height asymmetry. This model is in agreement with the observation from microscopic studies [23] that light emission occurs from discrete areas near to the surface of the particles. It also agrees with the observation [24] that unconfined ACEL particles rotate until their long axes are parallel to the field (in order that their positive and negative space charges can get as close to the appropriate electrode as possible).…”

AC powder electroluminescent displays

“…50-80-nm Cu x S precipitates from x-ray mapping of a transmission electron microscope, and a fourth is a recent article by Warkentin et al 26 who maintained that copper sulphide is present in the form of tiny CuS-like clusters by means of EXAFS. However, others have found no evidence for copper sulphide needles, 27,28 thus the precise nature of the role of copper sulphide clusters and the charge-generation process presently remain open to conjecture.…”