Strong green upconversion emission from Er3+–Yb3+ co-doped KCaBO3 phosphor

Potassium calcium mixed borate, KCaBO3:Er3+, phosphors with varied Yb3+ concentrations were synthesized by solid-state reaction and studied for the first time. The obtained single monoclinic phased polycrystalline phosphor has the capability of accepting the Yb3+ sensitizer up to 16 wt.%. Monotonically increasing green upconversion emission (2H11/2,4S3/2 → 4I15/2) of Er3+ with the increase of Yb3+ concentration is observed under 980 nm laser excitation. Upconversion mechanism is investigated in detail and attributed to the efficient resonant energy transfer from Yb3+ to Er3+ ions in such system. Our results suggest a potential material for green upconversion phosphor.