Anomalous thermal quenching of luminescence in ZnS:Cu phosphor crystals

Abstract

We studied the thermal quenching of luminescence (TQL) in the case of photoexcitation (PE, λ_e=313 and 365 nm) and cathodoexcitation (CE) with a high excitation density (∼10¹⁸ cm⁻³· sec⁻¹) in ZnS:Cu single crystals with various degrees of copper supersaturation, EL-455 and K-83 copper-activated powders, and ZnS∶Cu epitaxial thin films. Our study of TQL in the blue and green bands showed that two types of quenching anomalies are observed in the specimens used. An anomaly of the first type manifests itself in the fact that, with band-to-band excitation (λ_e = 313 nm and CE). the green band is quenched earlier than the blue band and small steps are observed on the quenching front. This anomaly is explained with the aid of a dislocation model of the blue center. An anomaly of the second type is observed in specimens not supersaturated with copper and consists of the quenching of luminescence beginning earlier at a high excitation (CE) density than at a low excitation (PE) density and proceeds in the same way in the blue and green bands. The thermal depths of the acceptors level are estimated from TQL for the three fundamental luminescence bands 440, 468, and 525 nm which are equal to 0.38 ±0.05, 0.7–0.8, and 0.9–1 eV, respectively.