Blue Cathodoluminescence from Highly Er-Doped ZnO Thin Films Induced by the Phonon Bottleneck Effect

The room-temperature blue cathodoluminescence (CL) from highly Er-doped ZnO thin films has been studied by using different electron beam currents (EBCs). The ZnO:Er thin films used in our experiment were prepared by simultaneous evaporation from two sources. The x-ray diffraction spectra show that the thin films have a strong preferential c-axis (0002) orientation with a hexagonal crystalline structure. The blue emission at 455 nm originating from the intra-4f shell transition (⁴F_5/2.⁴I_15/2) in Er³⁺ ions was observed at room temperature. The nonlinear dependence of the CL intensity on the EBC shows a more intense blue emission above the threshold EBC of 0.6μA, which is attributed to the phonon bottleneck effect.