Evidence for the direct impact excitation of Mn centers in electroluminescent ZnS:Mn films

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Abstract
In order to clarify the excitation mechanism of Mn luminescent centers in ZnS:Mn electroluminescent thin films, time-resolved emission spectra in photoluminescence and electroluminescence were measured. In photoluminescence, both emissions arising from ZnS host and Mn centers were observed. For the emission arising from Mn centers, the time delay showing energy transfer from ZnS host to Mn centers was recognized. In electroluminescence, contrary to this, the emission from the ZnS host was hardly observed, and the emission from Mn centers was observed immediately after excitation. These experimental results strongly suggest that the excitation mechanism of Mn centers in electroluminescence is due to the direct impact excitation of Mn centers by hot electrons accelerated in the high electric field in the Zns host. These results are also supported by efficiency measurements.