Tunable emission properties of Eu ions in KBPO4 (B = Ca, Sr, and Ba) via variation in their valence states

초록

We investigated the luminescent behavior of KBPO4 (KBPO4:Eu) nanocrystals (NC) doped with europium (Eu) ions, where B = Ca, Sr, and Ba. The NC samples were fabricated via the chemical method and annealed in different ambient environments for regulating the number of oxygen vacancies in the NCs. We observed that the as-synthesized KBPO4:Eu exhibited red emissions, which is a characteristic of Eu3+. In the H-2-annealed samples, where the number of oxygen vacancies increased via the reduction process, the orange-red luminescence from Eu3+ was considerably suppressed and blue emission from Eu2+ was significant. After subsequent O-2-annealing to decrease oxygen vacancies via oxidation, the red emissions of the KBPO4:Eu were recovered. This reversible conversion between Eu2+ and Eu3+ occurred commonly in the NCs irrespective of B ions. The results suggest that H-2/O-2-annealing in the local environment around the Eu ions can control the valence states of Eu ions and the related emission color of KBPO4:Eu.

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