Dye-Sensitized Downconversion

Splitting one high-energy photon into two lower energy photons through downconversion has been demonstrated for a variety of combinations of rare earth (RE) ions. However, the low absorption cross section of RE³⁺ 4f-4f transitions hampers practical application. Therefore, enhancing the absorption by sensitization is crucial. We demonstrate efficient dye-sensitized downconversion using a strong blue/UV absorbing Coumarin dye to sensitize downconversion of the Pr³⁺-Yb³⁺ couple in NaYF₄ nanocrystals (NCs). Luminescence spectra and lifetime measurements reveal Förster resonant energy transfer (FRET) from Coumarin to Pr³⁺ in NaYF₄:Pr³⁺Yb³⁺ NCs, followed by downconversion, resulting in Yb³⁺ IR emission with ∼30 times enhancement. The present study demonstrates the feasibility of dye-sensitized downconversion as a promising strategy to engineer strongly absorbing downconversion NCs to enhance the efficiency of photovoltaic cells.