Postsynthesis Doping of Mn and Yb into CsPbX3 (X = CI, Br, or I) Perovskite Nanocrystals for Downconversion Emission

Doping Mn and Yb into CsPbX3 (X = Cl, Br, or I) nanocrystals (NCs) yields luminescence due to de-excitation through d-d (yellow-red emission) and f-f transitions (near-infrared emission), respectively. However, to date, both Mn emission and Yb emission have been obtained from perovskite NCs with a wider band gap (<480 nm). To overcome this problem, we have developed a postsynthesis doping method in which Mn and Yb can be easily doped into preformed CsPbX3 NCs with band gaps in the entire visible region. Different morphologies like nanoplatelets and nanocubes are doped. Because we dope preformed host NCs, the effect of dopants on optical properties can be studied more reliably using the same batch of host NCs for both undoped and doped samples. We find that the problem of the absence of Mn emission from Mn-doped CsPbBr3 NCs can be overcome by suppressing back energy transfer from Mn to host NCs, either by increasing the band gap of the host by quantum confinement or by measuring photoluminescence at lower temperatures. Interestingly, dopants are found to enhance the excitonic emission intensities and reduce the Urbach absorption tail, suggesting a reduced defect density compared to that of undoped NCs. These added functionalities and capability to dope lower-band gap materials can be explored further for near-infrared light-emitting diodes, sensing, and luminescent solar concentrators of desired colors.