Heterogeneous Semiconductor Shells Sequentially Coated on Upconversion Nanoplates for NIR-Light Enhanced Photocatalysis

Rare Earths-Doped and Ceria-Coated Strontium Aluminate PlateletsVersatile Luminescent Platforms for Correlated Lifetime Imaging by Multiphoton FLIM and PLIM

We report our recent advances in the design and synthesis of functional and hybrid composite nanomaterials with properties geared toward life sciences assays and as platforms for biomedical imaging applications. Using a stepwise reverse micelle procedure, we synthesized hybrid platelets comprising rare earth-doped strontium aluminate cores labeled Eu,Dy:SrAlO, where the phase nominally denoted as Sr0.95Eu0.02Dy0.03Al2O4 dominates the nature of the composite, as demonstrated by extensive X-ray diffraction investigations. These were coated with a biocompatible cerium oxide shell, giving rise to the hierarchical hybrids denoted CeO2@Eu,Dy:SrAlO. Such Eu/Dy codoped strontium aluminates exhibit broad luminescent emissions with high optical sensitivity. The CeO2 shell further imparts biocompatibility and water dispersibility, resulting in kinetically stable nanoplatelets which can translocate into living cells in lifetime imaging protocols that were optimized for imaging across nano- and microscales. Multiphoton fluorescence lifetime imaging microscopy (MP FLIM) confirmed the luminescent properties in thin films and living cellular environments. These nanohybrids represent a significant step forward in the development of functional molecules and materials, leveraging directed and self-assembly strategies for their synthesis. Their luminescence (detectable by fluorescence as well as phosphorescence emission intensity correlated with emission lifetime), negligible toxicity on the time scale of imaging assays and up to 72 h, and biocompatibility with cellular milieu enabled their tracing with living cells. Their cellular activity was estimated by standard MTT assays in PC-3 and provided a further insight into their behavior in biological environments. The inclusion of heavy cerium and strontium atoms enhanced X-ray attenuation, supporting multimodal imaging by integrating optical and X-ray-based methods, which paves the way for potential applications in computed tomography correlated to confocal microscopy coupled with fluorescence lifetime imaging. These findings highlight the versatility of these luminescent hybrids for bioimaging and as synthetic scaffolds toward nanomedicine applications, bridging advanced imaging modalities with functional materials design.

Heterogeneous photocatalysis in flow chemical reactors

The synergy between photocatalysis and continuous flow chemical reactors has shifted the paradigms of photochemistry, opening new avenues of research with safer and scalable processes that can be readily implemented in academia and industry. Current state-of-the-art photocatalysts are homogeneous transition metal complexes that have favourable photophysical properties, wide electrochemical redox potentials, and photostability. However, these photocatalysts present serious drawbacks, such as toxicity, limited availability, and the overall cost of rare transition metal elements. This reduces their long-term viability, especially at an industrial scale. Heterogeneous photocatalysts (HPCats) are an attractive alternative, as the requirement for the separation and purification is largely removed, but typically at the cost of efficiency. Flow chemical reactors can, to a large extent, mitigate the loss in efficiency through reactor designs that enhance mass transport and irradiation. Herein, we review some important developments of heterogeneous photocatalytic materials and their application in flow reactors for sustainable organic synthesis. Further, the application of continuous flow heterogeneous photocatalysis in environmental remediation is briefly discussed to present some interesting reactor designs that could be implemented to enhance organic synthesis.

Modulation of lanthanide luminescence via an electric field

The modulation of luminescence via external stimuli such as temperature, mechanical stress, hydrostatic pressure, as well as electric and/or magnetic fields, has witnessed great progress, enabled the disclosure of new principles and energy transfer pathways, and widened applications. However, investigations on the luminescence modulation of lanthanide ions doped in semiconductors via an applied electric field are still absent. Herein, for the first time, we have demonstrated the in situ, real-time, and reversible modulation of the luminescence of Eu³⁺ doped in SnO₂ nanocrystals by manipulating the recombination rate of photo-generated electrons and holes, and the accompanied energy transfer mode in terms of linear and quasi-sinusoidal, from semiconductor to lanthanide ions. Following the same principle, the modulation of near infrared responsive Er³⁺ in SnO₂ and the visible luminescence of perovskite nanocrystals is further realized. This study offers extra methodologies for luminescence modulation, in addition to those already reported for ferro- and/or piezoelectric-hosted luminescent materials.

Lanthanide Doped Near Infrared Active Upconversion Nanophosphors: Fundamental Concepts, Synthesis Strategies, and Technological Applications

Near infrared (NIR) light utilization in a range of current technologies has gained huge significance due to its abundance in nature and nondestructive properties. NIR active lanthanide (Ln) doped upconversion nanomaterials synthesized in controlled shape, size, and surface functionality can be combined with various pertinent materials for extensive applications in diverse fields. Upconversion nanophosphors (UCNP) possess unique abilities, such as deep tissue penetration, enhanced photostability, low toxicity, sharp emission peaks, long anti-Stokes shift, etc., which have bestowed them with prodigious advantages over other conventional luminescent materials. As new generation fluorophores, UCNP have found a wide range of applications in various fields. In this Review, a comprehensive overview of lanthanide doped NIR active UCNP is provided by discussing the fundamental concepts including the different mechanisms proposed for explaining the upconversion processes, followed by the different strategies employed for the synthesis of these materials, and finally the technological applications of UCNP, mainly in the fields of bioimaging, drug delivery, sensing, and photocatalysis by highlighting the recent works in these areas. In addition, a brief note on the applications of UCNP in other fields is also provided along with the summary and future perspectives of these materials.

Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF₄ sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF₄ coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb³⁺, Er³⁺ and Dy³⁺. NaGdF₄:Yb,Er@NaDyF₄ core–shell nanoparticles with ultrathin layer shells exhibited a better T₁-weighted MR contrast.

In this work, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process.

Fabrication of luminescent TiO2:Eu3+ and ZrO2:Tb3+ encapsulated PLGA microparticles for bioimaging application with enhanced biocompatibility

Rare earth is of great interest because of their unique optical properties, especially the rich luminescent spectra. In this study, we developed a facile one-pot microwave-assisted synthesis of luminescent Eu³⁺ doped TiO₂ nanoparticles and Tb³⁺ doped ZrO₂ nanoparticles. As a result, the emitting centers (Eu³⁺ and Tb³⁺) were all well dispersed in the amorphous host oxide materials, leading to high luminescence. The obtained TiO₂:Eu³⁺ and ZrO₂:Tb³⁺ nanoparticles were then encapsulated into PLGA microparticles for bio-applications. These luminescent microparticles were then proven to be highly stable, biocompatible and of low cytotoxicity. We successfully demonstrated the bioimaging of live cells using the red-luminescent TiO₂:Eu³⁺ nanoparticles and green-luminescent ZrO₂:Tb³⁺ nanoparticles embedded PLGA microparticles. The microwave-assisted synthetic methodology can be further developed to be general method to prepare oxide nanoparticles.