Polar-Solvent-Free Sonochemical Synthesis of Mn(II)-Doped CsPbCl₃ Perovskite Nanocrystals for Dual-Color Emission

We present a facile, one-step, polar-solvent-free sonochemical synthesis of a series of Mn-doped CsPbCl3 perovskite nanocrystals (PNCs) by varying the Pb-to-Mn ratio, after which their structure, morphology, and temperature-dependent photoluminescence (PL) properties are investigated. The partial substitution of Pb2+ with Mn2+ in CsPbCl3 PNCs caused lattice contraction without affecting the morphology and structure. All Mn-doped PNCs exhibited dual-wavelength PL profiles, with a weak violet band at around 410 nm attributed to band-edge exciton and a strong orange band at around 596 nm attributed to Mn2+:4T1→6A1 transition, benefited by the exciton-to-Mn2+ energy transfer. Furthermore, Mn doping increased the PL quantum yield (PLQY) from 5.1% in CsPbCl3 to 41.14% for 11.8% Mn-doped PNCs as well as decay lifetimes from nanoseconds to milliseconds (long-lived emissive states). Owing to the thermally assisted transition from the exciton to 4T1 energy level of Mn2+, the temperature-dependent steady-state PL and time-resolved PL spectra of exciton and Mn2+ in Mn-doped CsPbCl3 PNCs displayed unusual and contradictory trends. The ultrasonication synthesized Mn-doped PNCs exhibited superior long-term stability, retaining 62% (@ RH 75%) of the initial PL without requiring additional encapsulation. To evaluate the suitable application of Mn-doped CsPbCl3 PNCs in the white light-emitting diode (w-LED) as a display system, we built a prototype w-LED using blue-, green-, and orange-emitting CsPb(Cl0.5/Br0.5)3, CsPbBr3, and Mn-doped CsPbCl3-coated glass slices onto a 20 mA UV LED chip. The constructed prototype w-LED generated bright white light, achieving a luminous efficiency of 76.3 lm/W, color rendering index of 81.4, R9 of 80.1, and a wide color gamut of 101.78% NTSC and 76% BT-2020, demonstrating its promising application in w-LEDs.