Fig. 2: Ho3+ doped CsPbI3 PQDs.

a TEM and HR-TEM (right) of undoped CsPbI3 and CsPbI3:Ho3+ (6.4%) PQDs. b XPS spectra of Ho3+ (4d) and Pb2+ (4 f) of undoped CsPbI3 and CsPbI3:Ho3+ (6.4%) PQDs. Absorption and emission spectra (c), and PLQYs and PL lifetime (d) of undoped CsPbI3 and CsPbI3:Ho3+ PQDs with different Ho3+ concentrations. e Mott–Schottky of CsPbI3 and CsPbI3:Ho3+ (6.4%) PQDs. f I-V curves with electron-only devices based on CsPbI3 and CsPbI3:Ho3+ (6.4%) PQDs