Fig. 6.

Generality of the proposed radiative energy transfer upconversion (RETU) for sensitizing photon upconversion in CsPbX₃ perovskite quantum dots (PeQDs). a Upconversion luminescence (UCL) spectra for LiYbF₄:0.5%Tm³⁺@LiYF₄ core/shell nanoparticles (NPs) and the NP-sensitized CsPbX₃ PeQDs (NPs: 1 mg mL⁻¹; PeQDs: 2 mg mL⁻¹) with varying halide compositions by casting them onto glass substrate under 980 nm CW diode laser excitation at a power density of 50 W cm⁻². The insets show the corresponding UCL photographs for the NP-sensitized PeQDs, and the scale bar represents 1 cm. b UCL spectra for NaYF₄:18%Yb³⁺, 2%Er³⁺ NPs (approximately 23 nm) and the NP-sensitized CsPbX₃ PeQDs (NPs: 1 mg mL⁻¹; PeQDs: 2 mg mL⁻¹) with varying halide composition under 980 nm CW diode laser excitation at a power density of 20 W cm⁻². The insets show the corresponding UCL photographs for the colloidal cyclohexane solution of the NP-sensitized PeQDs