We investigated the upconversion and downconversion luminescence in (Tb3+, Yb3+) and (Tb3+, Yb3+) co-doped lithiumlanthanum- aluminosilicate oxyfluoride glass. Upon excitation at 980 nm, where crystalline CdTe solar cells no longer absorb, the sub-bandgap photons can be converted to the higher-energy ones via upconversion. In addition, under excitation between 470 nm and 490 nm, one blue photon might be split up to two near-infrared ones via downconversion. The downconversion luminescence matches the spectral response of crystalline Si solar cell well. We observed much more intense upconversion luminescence from (Tm3+, Yb3+) codoped glass than that from ( Tb3+, Yb3+) codoped glass under the same 980 nm excitation conditions. Our results indicate that the sequential energy transfer from Yb3+ ions to Tm3+ ions is much more efficient than the cooperative energy transfer from Yb3+ ions to Tb3+ ions.
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