Xinyu Shen

Abstract:

Wide-coverage near infrared (NIR) phosphor-converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide-coverage NIR phosphors. Here, we report the single-component lanthanide (Ln³⁺ ) ions doped Cs₂ M(In_0.95 Sb_0.05 )Cl₆ (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd-Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs₂ M(In_1-x Sb_x )Cl₆ NCs can break the forbidden of f-f transition of Ln³⁺ , thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln³⁺ . Finally, the wide-coverage NIR LEDs based on Sm³⁺ , Nd³⁺ , Er³⁺ -tridoped Cs₂ K_0.5 Rb_0.5 (In_0.95 Sb_0.05 )Cl₆ NCs are fabricated and employed in the multiplex gas sensing and night-vision application.

Abstract:

Cesium lead halide perovskite nanocrystals (PNCs) exhibit promising prospects for application in optoelectronic devices. However, electroactivated near-infrared (NIR) PNC light-emitting diodes (LEDs) with emission peaks over 800 nm have not been achieved. Herein, we demonstrate the electroactivated NIR PNC LEDs based on Yb³⁺-doped CsPb(Cl_1-xBr_x)₃ PNCs with extraordinary high NIR photoluminescence quantum yields over 170%. The fabricated NIR LEDs possess an irradiance of 584.7 μW cm^-2, an EQE of 1.2%, and a turn-on voltage of 3.1 V. The ultrafast quantum cutting process from the PNC host to Yb³⁺ has been revealed as the main mechanism of electroluminescence (EL)-activated Yb³⁺ for the first time via exploring how the trend between the EL intensity of PNC and Yb³⁺ varies with different voltages along with the tendency of temperature- and doping-concentration-dependent PL and EL spectra. This work will extend the application of PNCs to optical communication, night-vision devices, and biomedical imaging.

Abstract:

AbstractThe dimension is a leading parameter in customization of unique optoelectronic properties of halide perovskite, while it is still challenging to achieve dimension control beyond the well‐developed composition regulation‐based strategy considering their intrinsic feature of ionic crystal. In this paper, ligands‐directed confinement effect is emphasized in rendering the reduced‐dimensional engineering of halide perovskite, and quasi‐2D (OAm)2CsPb2Br7 (n = 2) nanosheets are obtained by introducing a large amount of metal ions. As a representation, with Mg2+ participation, the initial adsorption of organic ligands (i.e., OA and OAm) to inorganic components (i.e., [PbBr6]4−) is promoted, conferring a ligands‐directed surface reconstruction to form the lamellar structure composed of alternate organic and inorganic layers. Namely, the inorganic–organic lamellar ensemble will play as a soft template, which effectively restricts the growth of [PbBr6]4− in the c‐axis direction even after the Cs‐OA injection, thus producing the anisotropic layered perovskite of (OAm)2CsPb2Br7 from CsPbBr3 scenario. Notably, such reduced‐dimensional engineering enables a remarkable luminescence tailoring, of which the deep blue emission centered at 439 nm is achieved. In addition, benefiting from such universal strategy, the luminescence is also dependent on the species of introduced metal ions (e.g., Ca2+, Co2+, Sr2+, and Mn2+).