Fluorescence in CdS and Its Possible Use for an Optical Maser

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Abstract
This paper discusses how the fluorescence from semiconductors might be useful in constructing an optical maser. Attention is given to the sharp line emission which occurs at low temperatures in CdS and which arises from excitons bound to impurities. Some recent experimental results are summarized which give information concerning the fluorescent efficiency and the depth to which crystals are excited using ultraviolet light for excitation. Possible maser geometries are discussed and the opportunities for using an evacuated ground state are pointed out. There appear to be several severe difficulties in the way of success. These are partly associated with the small depth of penetration of the exciting light, with the low fluorescent efficiencies available and with the inability to grow large perfect crystals with controlled impurity content. An improvement in the art of crystal growing is probably necessary before the effects described here can be expected to result in a useful optical maser.