报告题目：Near-infrared emitting Yb³⁺-doped lead-halide perovskite nanocrystals

报  告人：Aleksandr P. Litvin

报告时间：2024年5月24日9:40

报告地点：激光楼311

报告摘要：

The emission of lead-halide perovskite nanocrystals (NCs) is mostly in the visible spectral range. By doping perovskite NCs with lanthanides, their emission can be extended into the near-infrared (NIR) spectral region. Particularly, Yb³⁺-doped CsPbCl_xBr_3-x NCs exhibited strong NIR emission centered around 1 µm. To date, development of Yb³⁺-doped perovskite NCs included novel synthetic approaches, applications in solar harvesting, light detection and light-emitting devices. However, a deeper understanding of the fundamental processes governing the photoexcitation dynamics in these nanostructures is required for their rational design. Besides, the search for the new concept is beneficial for their broader application.

First, we shed light on the photoexcitation dynamics in Yb³⁺-doped CsPbCl_xBr_3−x perovskite NCs with different stoichiometries by investigating the temperature dependence of their PL properties. We developed a model in which the sensitization of Yb³⁺ ions occurs via intermediate trap states in the host matrix of CsPbCl_xBr_3−x NCs. The band gap of the NCs determines the energy gap between these trap states and the conduction band of the matrix, controlling the population of the trap states and the efficiency of energy transfer to Yb³⁺ ions. This mechanism, combined with the inherent temperature dependence of radiative recombination rates, explains the observed temperature-dependent PL properties of the Yb³⁺:CsPbCl_xBr_3−x NCs. The proposed model also explains the observed reduction of the NIR PL quantum yield upon gradual Cl-to-Br anion exchange and the absence of saturation of the NIR PL intensity in Yb³⁺:CsPbCl_xBr_3−x NCs at high excitation powers.

Next, we proposed that Yb³⁺-doped CsPbCl_xBr_3-x NCs can serve as versatile and efficient dual-band luminescent materials operating under two-photon NIR excitation, with excitation and emission occurring in the 1^st and 2^nd NIR optical windows, respectively. The gradual anion exchange (from Cl^- to Br^-) in these perovskite NCs is accompanied by a change of the bandgap resulting in a strong enhancement of their two-photon excited PL, with TPA cross-section reaching high value of 2.3×10⁵ GM. NCs can be embedded into silica microspheres and then coated with biocompatible polymer PEG offering a protective amphiphilic shell. The PEG-coated microspheres containing Yb³⁺:CsPbCl_xBr_3-x NCs could be easily dispersed either in toluene or in water and maintained their PL response under both one- and two-photon excitation, thus making them promising materials for biosensing, bioanalysis, and optical imaging of cells, viruses, and tissues.

报告人简介：

Aleksandr P. Litvin received his PhD in Optics in 2015 from ITMO University (St. Petersburg, Russia). From 2020 to 2022 he headed the Laboratory “Optics of Quantum Nanostructures” at the same university. He is currently a postdoctoral researcher at College of Materials Science and Engineering of the Jilin University. His main scientific interests are optical spectroscopy of near-infrared emitting nanostructures, including quantum dots, nanoplatelets, and perovskites, energy and charge transfer phenomena between nanoparticles, and their utilization in optoelectronic devices.