Abstract: Multifunctional inorganic luminescent nanostructures are of great interest for future multimodal precision bioimaging applications. Rare earth-doped nanophosphors have attracted special attention in the biomedical field due to their ability to combine optical properties with additional functionalities. Among these systems, magneto-luminescent nanoparticles stand out because they integrate simultaneously magnetic and luminescent properties into a single nanocomposite, thus enabling their use in multimodal biomedical applications. Such nanomaterials have been developed for purposes including their use as contrast agents in bioimaging, magnetic hyperthermia, as well as potential diagnostic and therapeutic strategies through non-invasive approaches. To enhance the physicochemical and biological properties of nanomaterials, mesoporous silica has been employeed as a multifunctional coating, due to their biocompatibility, high surface area, and the presence of surface Si–OH groups, which allow versatile functionalization and further biomedical applications such as drug delivery. In this work, we designed and developed multifunctional nanomaterials composed of different RE-doped nanoparticles combined with superparamagnetic Fe₃O₄ nanoparticles encapsulated in mesoporous silica. Magnetic hyperthermia experiments and cell viability assays demonstrated their potential biomedical applications. Luminescent properties were attributed to the f-f transitions depending on the RE ions, giving rise to intense emission in the UV-Vis region. The encapsulated nanocomposites exhibited a high surface area and superparamagnetic behavior derived from the magnetite component, showing the capacity to generate a significant temperature rise under exposure to an alternating magnetic field. Cell viability assays using the MTT method were conducted in HepG2, hepatic stellate cells (HSC), and Kupffer cells.  Our findings demonstrate that RE-doped nanophosphors integrated with superparamagnetic Fe₃O₄ encapsulated in a SiO₂ shell offer a multifunctional nanocomposite that integrates luminescent and magnetic properties with biocompatibility, showing promising potential for future applications in theragnostics.

Abstract: Integration of Spintronics and Optoelectronics, i.e., Optospintronics has the potential to combine the effect of light with the spins of charge carriers. In this attempt, two approaches have been adopted, i.e., Magnetic field tuning of photocurrent and Optical tuning of spin-valve effect. Focussing on the second approach, we have fabricated a coupled organic photodetector and organic spin-valve, i.e., a single Magnetic Organic Photodetector (MOPD) heterostructure, ITO/V[TCNE]​_x​/C₆₀/Co/Au. This MOPD heterostructure exhibits photocurrent generation at room temperature with 40% photocurrent to dark current ratio under illumination of 660 nm red laser light. Also, it shows room temperature negative magnetoresistance as high as -25.85% under dark. Moreover, according to our experimental evidences, this MOPD heterostructure exhibits spin-valve effect with peak up to 3% spin-valve magnetoresistance. Thus, this device can operate as an individual spin-valve, and a photodetector at room temperature. Significantly, coupling between spin-valve and photodetector characteristics is observed for the first time in this MOPD device. Such “cross-talk” between optical response and spin-valve property in a single device are highly significant for future development of novel optically controlled integrated memory logic devices, such as LiFi and Electro-Optical Hybrid Computing technologies. Topological Insulator (TI) based Low Noise, Broadband Infrared photodetector array at room temperature has been developed. Our fabricated heterostructure ITO/TI(Bi₂Se₃)/Co/Au transit from “admixture of bulk non-conducting and surface conducting state” to “dominating surface conducting state” via bias voltage. A positive photocurrent generation with an optimal photocurrent-to-dark current ratio of 9 × 10³ was achieved using broadband infrared light. Our device promises for IR detection and next-generation high-performance focal plane arrays.

Abstract: Lanthanide (Ln³⁺) ions are known for their unique near-infrared (NIR) luminescence resulting from forbidden 4f–4f (f–f) transitions, typically enabled through sensitization by antenna ligands. In this study, we present a homologous series of [L₂–Zn₂–Ln] complexes adopting a sandwich structure, where two ligands (L) coordinate symmetrically around the Ln center via zinc (Zn²⁺) nodes. Photophysical measurements in both the visible and NIR regions indicate a notable enhancement in NIR emission intensity in these sandwich complexes compared to their mono-ligand analogs. A key observation is the quenching of singlet-to-ground state (S₁ → S₀) fluorescence from the ligand, suggesting efficient energy transfer from the excited ligand to the Ln³⁺ ion. This enhanced transfer is attributed to improved electronic coupling and spatial proximity facilitated by the sandwich architecture. The results demonstrate that ligand environment and structural symmetry critically influence NIR luminescence. These findings establish [L₂–Zn₂–Ln] complexes as promising candidates for developing advanced NIR-emitting materials for use in optical sensing and optoelectronic applications.

Abstract: The carrier injection efficiency and confinement within the active region play a crucial role in determining the threshold and slope efficiency of GaN-based vertical-cavity surface-emitting lasers (VCSELs). In this study, two types of composition-graded epitaxial structures are proposed: a composition-graded last quantum barrier (LQB) and a composition-graded electron blocking layer (EBL). GaN-based optically pumped VCSELs incorporating these structures exhibit significant improvements over conventional composition-uniform designs, with threshold reductions of 71.1% and 53.2%, respectively. Band structure analysis reveals that these performance improvements are attributed to enhanced electron injection efficiency and improved hole confinement within the active region as well. Furthermore, pulsed lasing operation in electrically injected VCSELs is successfully demonstrated by employing the composition-graded LQB structure. This study systematically validates the effectiveness of the composition-graded LQB and EBL structures in enhancing GaN-based VCSEL performance from both theoretical and experimental perspectives. These findings provide valuable insights for the development of high-performance VCSELs.