Concentration Dependence of Green-Cu Luminescence in ZnS: Cu, Al

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Abstract
Mechanisms of concentration quenching of green-Cu luminescence in hexagonal ZnS:Cu,Al under cathode-ray excitation are investigated. The observed concentration dependence of the luminescence intensity is explained well by a model assuming complete pairing of donors and acceptors. Interstitial Cu+ centers are formed during synthesis, and their concentration is determined by thermodynamic equilibrium with other defects at the firing temperature. They act as recombination centers for free carriers and provide the dominant nonradiative path for excitation energy when Cu concentration is larger than that of Al. In the concentration region of excess Al, an Auger process is proposed as the dominant nonradiative relaxation process of excited donor-acceptor pairs. The free energy changes at 1200 C associated with formation of Schottky disorder and of interstitial from substitutional Cu+ ions are estimated as 3.64 and 2.97 eV, respectively.

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