Sequential tunability of red and white light emissions in Sm-activated ZnO phosphors by up- and downconversion mechanisms

Inorganic ZnO modified using rare earth (RE) ions is proposed as an alternative source of energy harvesting over the whole solar spectrum by utilizing the down- and upconversion excitation mechanisms. The present investigation reports the tunability of white/red light possessing excellent color rendering index and color quality scale by employing down/upconversions from Sm-activated ZnO phosphors. The occurrence of intra-4f transitions of Sm³⁺ ions in both up- and downconversion signifies the energy transfer from defect centers of the host lattice to the dopant sites (Sm³⁺). A mechanism is explicated with the help of an energy level diagram for down/upconversion to provide a clear understanding of the host–guest energy transfer and the involvement of various defect states. As a proof-of-concept, these findings demonstrate an inexpensive and clean approach to solid-state lighting and solar cell industries by extending the spectral range from the ultraviolet to infrared region.