Improving the Five-Photon Absorption from Core-Shell Perovskite Nanocrystals

Enhanced stability and optical performance of CsPbBr3@FAPbBr3 core-shell perovskite nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs), particularly CsPbBr3, have attracted considerable attention due to their remarkable optical properties, positioning them as promising candidates for optoelectronics and bioimaging. Despite their potential, challenges such as environmental degradation and structural instability persist. Core-shell architectures and encapsulation have emerged as effective strategies to address these issues. Here, we propose a double-shelling strategy aimed at the improvement of the optical properties of perovskite NCs and their stability under harsh environmental conditions. We demonstrate the synthesis of CsPbBr3@FAPbBr3 core-shell NCs, combining a luminescent CsPbBr3 core with a stabilizing FAPbBr3 shell via a hot-injection method. This approach allows for a significant enhancement of the photoluminescence quantum yield, extension of photoluminescence lifetimes, and improvement of the photo- and thermostability of NCs. For further reinforcement of moisture resistance, we encapsulated the core-shell NCs in a SiO2 shell to preserve their photoluminescence responses under one- and two-photon excitation in water and isopropanol. Additionally, the increased two-photon absorption cross-section of these NCs combined with water stability suggests their strong suitability for multiphoton imaging applications. This dual-shelling strategy offers a stable, high-performance perovskite-based nanomaterial, expanding the application potential of lead halide perovskite nanocrystals in light-emitting devices and bioimaging technologies.

Hot Carrier Cooling and Multiphoton Absorption of Quasi-Type II ZnSeTe-Based Quantum Dots

Ternary ZnSeTe quantum dots (QDs) are regarded as the most promising Cd-free blue emitters, while their fundamental optical properties such as hot carrier (HC) cooling process and multiphoton absorption (MPA) remain unclear, which will hinder their potential application. In this work, we compare the HC cooling processes of ZnSeTe/ZnSeS and ZnSeTe/ZnSeS/ZnS QDs and find that the HC cooling times of ZnSeTe/ZnSeS/ZnS QDs are insensitive to excitation intensity as a result of the suppressed hot-phonon bottleneck and Auger effect. Importantly, we have determined the two- to five-photon absorption cross sections of two kinds of QDs, highlighting the advantages of ZnS shells in enhancing MPA cross sections of ZnSeTe-based QDs. These insightful findings shed light on the underlying optical properties of ZnSeTe-based QDs and emphasize the critical role of the shell in engineering their HC cooling and MPA performance.

Exploiting the Photo-Physical Properties of Metal Halide Perovskite Nanocrystals for Bioimaging

Perovskite nanomaterials have recently been exploited for bioimaging applications due to their unique photo-physical properties, including high absorbance, good photostability, narrow emissions, and nonlinear optical properties. These attributes outperform conventional fluorescent materials such as organic dyes and metal chalcogenide quantum dots and endow them with the potential to reshape a wide array of bioimaging modalities. Yet, their full potential necessitates a deep grasp of their structure-attribute relationship and strategies for enhancing water stability through surface engineering for meeting the stringent and unique requirements of each individual imaging modality. This review delves into this evolving frontier, highlighting how their distinctive photo-physical properties can be leveraged and optimized for various bioimaging modalities, including visible light imaging, near-infrared imaging, and super-resolution imaging.