Photoluminescence of ZnS:TbF[sub 3] Thin Films

Photoluminescence from ZnS : TbF 3 evaporated films of approximately 1µ thick has been studied at room temperature as a function of the fluoride concentration. The excitation or pumping wavelength varies from 4880 to 2600Aå, while the Tb 3+ ( 5 D 4 → 7 F 5 ) emission transition at 5425Aå is monitored at the output. For pumping photon energies below the ZnS forbidden gap, the excitation spectra resemble that of the pure TbF 3 film or single crystal. For this case, the conversion efficiency with 4880Aå ( 7 F 6 → 5 D 4 ) pumping in samples that contain 0.86% TbF 3 is close to 100% as compared to 0.8% for pure TbF 3 . With pumping energies above the ZnS gap, photoluminescence presumably due to energy transfer from electron‐hole pairs has also been observed; however, such a process yields conversion efficiency generally in the 10−5–10−6 range. These results support the model that electroluminescence in devices using similar films arises from direct excitation of Tb 3+ levels by hot electrons as proposed by one of the authors.