Energy transfer from ZnO nanocrystals to Terbium (3+) ions: A spectral overlap study

In recent years, nanocrystals of the wide bandgap semiconductor zinc oxide (ZnO) have been widely studied due to its potential application in optoelectronics devices such as light source and detectors. ZnO nanocrystals (ZnO-nc) have a bandgp of 3.37eV and a large exciton binding energy of 60meV, which make them attractive material for devices which operate in the ultraviolet (UV)-blue region of the electromagnetic spectrum [1]. Consequently, ZnO-nc have also been used as sensitizers to excite the rare-earth(RE) ions such as Ce³⁺, Er³⁺, Ho³⁺, Nd³⁺, Tm³⁺, Dy³⁺, Eu³⁺ and Tb³⁺ [2–9] which absorb the UV-blue emission from the ZnO-nc and in turn emits their own light in the visible or infra-red wavelengths. ZnO-nc have been used as sensitizer mainly due to its large absorption cross-section and broad excitation spectrum [10] compared to the RE ions. Recently, our group has published a detailed study on the energy transfer mechanism from ZnO-nc to Eu³⁺ ions [11], which results in strong red emission from Eu³+ at 614nm. In the above mentioned study, the contribution of the various ZnO-nc emission centres, which has been identified to consist of seven de-excitation centres [12], in the energy transfer process to the Eu³⁺ ions was investigated. In this work, we continue to study the energy transfer contribution from the various ZnO-nc emission centres to the Tb³⁺ ions embedded in SiO2, based on the spectral overlap of ZnO-nc emission and Tb³⁺ ions excitation. The results from this study, along with our previous results on the energy transfer contribution from the various ZnO-nc emission centres to the Eu³⁺ embedded in SiO2 matrix [11], will help in fabricating proficient red, blue, green and even white light sources by combining the blue, green and red emissions from ZnO-nc, Tb³⁺ and Eu³⁺, respectively which can be used in various photonic applications.