Enhanced broadband emission from Er-Tm codoped ZnO film due to energy transfer processes involving Si nanocrystals

Er-Tm-Si codoped ZnO film was synthesized by co-sputtering, in which Si nanocrystals (Si-NCs) were observed to form by annealing at 1173 K for 30 min. A fairly flat emission with ∼375 nm bandwidth is achieved, and its intensity is enhanced by nearly an order of magnitude by the Si-NCs, which acted as broadband sensitizers, compared with that without Si-NCs. The film also exhibits broadband emission with relatively stable spectral shape under different excitation lines. The 1.80 μm emission intensity increases by a factor of 3 while the 1.53 μm emission is almost constant with decreasing the operating temperature from 300 to 20 K, attributed to competition between three energy transfer processes from Si-NCs to Er3+/Tm3+ and from Er3+ to Tm3+, and their back transfer processes.