Enhanced NIR downconversion luminescence by precipitating nano Ca5(PO4)3F crystals in Eu2+–Yb3+ co-doped glass

• Transparent Eu2+–Yb3+ co-doped glass ceramic containing nano-Ca5(PO4)3F was fabricated.
• Downconversion luminescence from Eu2+ to Yb3+ was enhanced by precipitating FAP nanocrystals.
• Phonon energy of FAP crystal remedy energy gap between Eu2+ to Yb3+.

Eu2+–Yb3+ co-doped transparent glass–ceramic containing nano-Ca5(PO4)3F (FAP) was prepared in reducing atmosphere. XRD and TEM analysis indicated that nano-FAP about 40 nm precipitated homogeneously in glass matrix after heat treatment. Confirmed by spectroscopy measurements, the crystal-like absorption and emission of Eu2+ indicated the partition of Eu2+ into FAP nanocrystals in glass ceramic. NIR emission due to the transition 2F5/2→2F7/2 of Yb3+ ions (about 980–1100 nm) was observed from glasses under ultraviolet excitation, ascribed to downconversion from Eu2+ to Yb3+, which can be enhanced by precipitating nano-FAP crystals. The results indicated that Eu2+–Yb3+ co-doped glass–ceramic embedding with nano-FAP is a promising candidate as downconversion materials for enhancing conversion efficiency of solar cells.

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