Photoluminescence of ZnS : TbF₃ Thin Films

Photoluminescence from 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 Tb³⁺ emission transition at 5425Aå is monitored at the output. For pumping photon energies below the forbidden gap, the excitation spectra resemble that of the pure film or single crystal. For this case, the conversion efficiency with 4880Aå pumping in samples that contain 0.86% is close to 100% as compared to 0.8% for pure . With pumping energies above the 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 Tb³⁺ levels by hot electrons as proposed by one of the authors.