Abstract
Single crystals of ZnS: Cu,Al and ZnS: Ag,Al were grown from the melt under high pressure by the Bridgman method. It was found that a remarkable broad band absorption appears in an infrared region of 3 to 14 μ under simultaneous ultraviolet illumination. This absorption is ascribed to the transition of electrons trapped at shallow donor states due to aluminum to the conduction band. The observed spectra are analyzed in terms of the theories of the effective mass approximation and the k·p perturbation. A good agreement is obtained between experiment and theory. The optical and thermal ionization energies for donor electrons are found to be 0·100 and 0·074 eV, respectively, and the electron effective mass is determined to be (0·34 ± 0·02) m 0. This type of infrared absorption was found to be associated only with the green-Cu and blue-Ag luminescences. Some discussions are presented as to the correlation of this infrared absorption-with the visible luminescence.
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