Excitation Mechanism of Luminescence Centers in Nanostructured ZnS:Tb,F Thin-Film Electroluminescent Devices

Abstract

The excitation mechanism of luminescence centers has been studied in a low-operation-voltage nanostructured (NS-) ZnS:Tb,F thin-film electroluminescent (TFEL) device, of which emission layer is a multilayer composed of 4.5-nm-thick ZnS:Tb,F nanocrystal layers and 0.7-nm-thick insulating interlayers. The EL intensity ratio of the ⁵D₃ excited level to the ⁵D₄ excited level of Tb³⁺ increased with operation voltage, which revealed that the dominant mechanism is the direct-impact excitation of luminescence centers by hot electrons. Moreover, the intensity ratio observed from the ZnS:Tb,F NS-TFEL device was greater than that observed from the conventional TFEL device, which implies that the energy distribution of hot electrons in the emission layer of the NS-TFEL device shifts to a higher energy compared with that in emission layer of the TFEL device. These assumptions are discussed in conjunction with similar results obtained using Tm³⁺ as an alternative luminescence center in the NS-TFEL device.