Energy transfer process to the emission center for the electroluminescence of ZnS thin films and the pure blue-emitting devices

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1. In order to clear the excitation process of the emission center for ZnS thin film electroluminescent devices, various devices were fabricated and several emission properties were measured. The following results were obtained.(1) The transient characteristics in ZnS thin-films doped with Tb^<3+> ions or Mn^<2+> ions under an alternating pulse voltage with very short width were measured. The emission from the Tb^<3+> ions and Mn^<2+> ions saturated within the applied pulse voltage. Broad-band emission intrinsic to the ZnS host was observed in the wavelength region from 320nm to 700nm with very short lifetime. The observed emission from Tb^<2+> ions and Mn^<2+> ions are superimposed on the broad-band emission and delayed to the broad-band emission from the ZnS host.(2) The transient behavior of the photoluminescence show similar characteristics to that in electroluminescence.(3) The 350nm emission from the ZnS host, Mn^<2+> emission and Tb^<3+> emission show a similar tendency toward the dependence of annealing temperature in electroluminescence.(4) The precious results for understanding the excitation process of the emission center were observed from the experimental results of ultravioletmlight irradiation on electroluminescence.(5) From these results, it is concluded that the emission center of the electroluminescent devices are excited by the energy transfer from the hosts.2. Blue-emitting electroluminescent devices doped with Tm^<3+> ion were fabricated on the basis of the excitation process, and the following results were obtained.(1) As the emission center, TmOF center is more efficient than TmF_x center.(2) As the host materials for Tm-ion-doped EL devices, several hosts were investigated. The most dominant lines in these emission varied with the kind of host materials. The spectral line shifted to a shorter-wavelength region with increase of the band-gap energy of host materials.