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

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 CsPbX 3 (X = Cl, Br, and I) perovskite quantum dots . However, the realization of nonlinear upconversion luminescence (UCL) from these all-inorganic CsPbX 3 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 CsPbX 3 perovskites based on fluorescence resonance energy transfer (FRET), where all-inorganic CsPbX 3 perovskites and upconverting CaF 2 :Ln (Ln = Yb 3+ /Er 3+ , Yb 3+ /Ho 3+ , and Yb 3+ /Tm 3+ ) nanocrystals are closely integrated with each other as a whole by using a modified two-step epitaxial growth approach, forming the unique upconverting CsPbX 3 /CaF 2 :Ln hetero-structured nanocomposites (HSNCs). Benefitting from the extremely high FRET efficiency of ∼99.7%, excitonic UCL from CsPbX 3 perovskites can be realized upon low-power density 980-nm diode laser irradiation. More importantly, all the HSNCs are found to outperform their pure CsPbX 3 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 CsPbX 3 perovskites for high-performance optoelectronic and photovoltaic applications.