Effect of phase transition on photoluminescence of Er-doped KNN ceramics

The lead-free ceramics K_0.5Na_0.5NbO₃ doped with x mol% Er³⁺ ions have been successfully manufactured and their photoluminescence properties, including the up-conversion visible (480–700 nm) emissions, down-conversion near infrared (1400–1680 nm) and middle infrared (2620–2850 nm) emissions, emission colors and lifetimes of the energy levels have been systemically investigated. The corresponding photoluminescence mechanism has been discussed in detail. Our results show that the Er-doping induces a phase transition from orthorhombic to cubic-like as well as inhibits the grain growth due to the donor-type nature. Both the change of crystallographic structures and concentration-quenching effect induced by Er³⁺ ions have great influences on the photoluminescence properties. Because of the wide emission ranges and long lifetimes, Er-doped K_0.5Na_0.5NbO₃ ceramics are the promising candidates for optoelectronic applications. - Highlights: • Er-doped KNN ceramics are prepared to study the photoluminescence properties. • Up-conversion Vis, down-conversion NIR/MIR emissions and lifetimes are studied. • The concentration quenching effect and energy transfer processes are investigated. • The phase transitions and PL properties can be modulated by adjusting Er contents. • Er-doped KNN ceramics have great potential in the optoelectronic applications