Color tunable upconversion luminescence of Er³⁺ -Yb³⁺ codoped KY₃F₁₀ prepared by a hydrothermal treatment

The KY3F10: Er3+, Yb3+ upconversion (UC) phosphor was prepared using a hydrothermal technique. The study investigated the impact of sample structure, morphology, Er3+ doping concentration, and annealing time on the UC emission properties. The results revealed that the synthesized samples had cubic KYb3F10 structures, with a block size of approximately 200-500 nm for the 12-hour annealed sample, which reduced to a grain size of 50-100 nm for the 5-hour annealed sample. Intense UC light emission was observed in the sample at 1.0%Er3+, and 10%Yb3+ doping concentration for an annealing time of 12 h. Their respective peak emissions were measured at 551 and 665 nm, with green light visible to naked eye. The color purity of the green light was estimated to be 96.7%, while the decay time for the green emission light was 557.6 ms and 716.2 ms for red emission light. When the annealing time of the 1.0% Er3+, 10% Yb3+ doping sample was shortened to 5 h, the light color changed to bluish-white. The correspounding peak emissions were measured at 479 nm, 547 nm and 654 nm. These findings suggest that the annealing time has a substantial impact on both the sample size and UC luminescence. The study also discusses the UC luminous mechanism in detail.