Tunable visible upconversion emission in Er3+/Yb3+-codoped KCaBO3 phosphors by introducing Ho3+ ions

• Multicolor upconversion emission from Ho3+-codoped KCaBO3:Er3+,Yb3+ phosphors is investigated.
• Wide range color tunability from green to red from the selection of Ho3+-content.
• The upconversion process dominated by two photon absorption and efficient inter-ion energy transfer.
• Our results suggest a potential material for green, yellow and red upconversion phosphors.

Herein, the tunable upconversion (UC) emission from KCaBO3 phosphors, codoped with fixed Er3+,Yb3+ and various Ho3+-concentrations, has been demonstrated. Under 980 nm laser excitation, strong tunability from green to red color emission was successfully achieved via controlling the Ho3+-codoping in KCaBO3:Er3+,Yb3+,xHo3+ phosphor due to efficient two-photon excitations and inter-ion energy transfer (from Yb3+ to Er3+/Ho3+) mechanisms. Substantial decrease in the green–red intensity ratio from 3.94 to 0.21 and systematic enhancement in energy transfer efficiency (η), with the increment of Ho3+-content, supported the above mechanisms.