Fig. 4.

Mechanistic investigation of the radiative energy transfer upconversion (RETU) process in nanoparticle (NP)-sensitized CsPbX₃ perovskite quantum dots (PeQDs). a CsPbBr₃ concentration-dependent upconversion luminescence (UCL) spectra for LiYbF₄:0.5%Tm³⁺@LiYF₄ core/shell NP-sensitized CsPbBr₃ PeQDs with NPs concentration of 1 mg mL⁻¹ under 980 nm excitation at a power density of 50 W cm⁻². b Integrated intensities of the Tm³⁺ emissions at 347, 362, 450, 483, and 648 nm and the CsPbBr₃ emission at 520 nm vs. the CsPbBr₃ concentration, as obtained from (a). c UCL decays from ¹D₂ of Tm³⁺ by monitoring the Tm³⁺ emission at 362 nm in NP-sensitized CsPbBr₃ PeQDs with varying CsPbBr₃ concentrations under 980 nm excitation. d UCL lifetimes of ¹I₆, ¹D₂, and ¹G₄ of Tm³⁺ in NP-sensitized CsPbBr₃ PeQDs vs. the CsPbBr₃ concentration