Photon upconversion of all-inorganic CsPbX3 quantum dots based on fluorescence resonance energy transfer in hetero-structured perovskite/upconversion nanocomposites

Abstract Photo upconversion that converts low-energy light into high-energy photons holds great promise for boosting the energy conversion efficiencies particularly for photovoltaic devices based on all-inorganic CsPbX3 (X = Cl, Br, and I) perovskite quantum dots. However, the realization of nonlinear upconversion luminescence (UCL) from these all-inorganic CsPbX3 perovskites has been met with very limited success until now. Herein, we propose a rational perovskite/upconversion hetero-structured design strategy to achieve excitonic UCL of all-inorganic CsPbX3 perovskites based on fluorescence resonance energy transfer (FRET), where all-inorganic CsPbX3 perovskites and upconverting CaF2:Ln (Ln = Yb3+/Er3+, Yb3+/Ho3+, and Yb3+/Tm3+) nanocrystals are closely integrated with each other as a whole by using a modified two-step epitaxial growth approach, forming the unique upconverting CsPbX3/CaF2:Ln hetero-structured nanocomposites (HSNCs). Benefitting from the extremely high FRET efficiency of ∼99.7%, excitonic UCL from CsPbX3 perovskites can be realized upon low-power density 980-nm diode laser irradiation. More importantly, all the HSNCs are found to outperform their pure CsPbX3 counterparts in terms of air-stability, thermal-stability, and excitonic downconversion luminescence intensity, clearly demonstrating the overwhelming advantages of upconverting HSNCs we prepared over the pure CsPbX3 perovskites for high-performance optoelectronic and photovoltaic applications.