North Eastern Hill University

Novel fluorescence probes, PyQ1-PyQ4, based on 2-pyridyl quinoline moiety were developed and thoroughly investigated for solvent dependent fluorescence modulation and metal sensing ability. The estimated photophysical properties reveal significant solvatochromic effect on fluorescence Stokes shift ranging within 2318-7480 cm(-1) in different solvents. Likewise, fluorescence yields and lifetime show the variation of about 40 and 14 times, respectively indicating strong solvent dependent fluorescence behaviour. The PyQ derivatives exhibit a distinct fluorescence "turn-off" behaviour in the presence of Cu(II) ions, highlighting their potential for selective Cu(II) detection among other metal cations. The results demonstrated that all the four probes exhibited almost similar to 98 % fluorescence intensity decrease upon binding through quinoline nitrogen atoms to copper ion in 1:1 stoichiometry. Theoretical calculation results using density functional theory (DFT) and natural bond orbital (NBO) analysis predict significant ligand to metal excited state charge redistribution in presence Cu(II) ions, leading to the chelation enhanced quenching (CHEQ) of fluorescence. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.0-2.4 mu M in different cases. Additionally, PyQ1 behaves as a ratiometric fluorescent probe for the detection of Zn(II) and Hg(II) with the corresponding LODs of 4.2 mu M and 11.0 mu M, respectively. The results underscore the potential application of the developed PyQ derivatives as solvatochromic probe with significant modulated fluorescence response in presence of certain metal ions.

This paper discusses the synthesis of Bare BiOBr, Zn-doped BiOBr (Zn-BiOBr), and Gd-doped BiOBr (Gd-BiOBr) photocatalysts synthesized through a solvothermal route to degrade reactive dyes in the presence of visible light. The effective incorporation of dopant was verified by structural and modifying electronic properties. Doping altered the morphology of the microspheres and this caused a boost in surface area. Optical studies showed bandgap narrowing and notably reduced electron-hole recombination in Gd-BiOBr. Photocatalytic tests under visible light with ultrasonic assistance revealed that Gd-BiOBr achieved 98% degradation efficiency after 5 runs, with minimal structural changes and mass loss. An increase in charge transfer and reactive oxygen species (ROS) production was suggested by transient photocurrent and scavenger tests. Beyond dye degradation, the photocatalysts, especially Gd-BiOBr, show promise for treating emerging pollutants such as antibiotics and heavy metals, expanding their potential in environmental remediation.

In this study, pure and nickel-doped tin oxide (SnO₂) nanoparticles were successfully synthesized via wet-chemical method to investigate their structural, optical, and photocatalytic properties, with a focus on enhancing its photodegradation efficiency for decomposing Reactive Blue 19 (RB 19) dye under UV-Vis light irradiation. Field emission scanning electron microscopy (FESEM) analysis revealed that Ni doping significantly influenced the surface morphology of SnO₂, increasing surface roughness. Energy-dispersive analysis of X-rays (EDAX) spectroscopy and elemental mapping analysis confirmed uniform and successful incorporation of Ni²⁺ into the SnO₂ lattice. X-ray diffraction (XRD) study indicated that all samples retained the tetragonal rutile structure, with no secondary phases, confirming substitutional doping. A reduction in crystallite size and minor peak shift for the doped samples suggested a minimal lattice distortion and increased microstrain due to Ni incorporation. UV–Vis absorption spectra showed strong UV absorption in pure SnO₂, which slightly red-shifted for Ni-doped samples, indicating band gap narrowing due to sp–d exchange interactions and the formation of localized energy states. These modifications, along with the generation of oxygen vacancies, improved visible-light responsiveness. Photocatalytic experiments showed that Ni-doped SnO₂ significantly outperformed pure SnO₂ in degrading RB 19 dye, following pseudo-first-order kinetics. Enhanced performance of the Ni-doped samples was attributed to improved charge separation and increased active surface sites. Optimal catalytic activity of 90.64 % was also achieved at lower photocatalyst loading concentration. The recyclability tests confirmed over 83.44 % efficiency retention after four cycles. These findings highlight the potential of Ni-doped SnO₂ as a stable and efficient photocatalyst for wastewater treatment applications.

The Eu3+-doped CaY2O4 phosphors were synthesised via high-temperature solid-state method. The XRD analysis suggests an Orthorhombic-like phase of the phosphor, with Eu3+ ions effectively substituting Y3+ sites, while the crystallite size analysis (Scherrer and W-H) reveals dopant-induced grain growth accompanied by strain relaxation. The photoluminescence spectra show an intense red-emission at 610 nm under a broad UV-to-blue excitation, with 466 nm emerging as the most efficient excitation wavelength, highlighting compatibility with blue LED sources. Concentration quenching behaviour suggests excitation-wavelength dependence, with optimum Eu3+ concentration at 1.5 mol% under deep UV-excitation (257 nm), and 2 mol% under near-UV/visible (393-532 nm) excitations. Dexter analysis indicates the dipole-dipole interactions dominated quenching in the visible region, while the unusually low Q value under deep UV-excitation suggests the host-activator transfer. The Judd-Ofelt analysis indicates a non-centrosymmetric Eu3+ environment, and CIE coordinates (x = 0.643, y = 0.356) with similar to 94 % high colour purity demonstrates the saturated red emission. Thermoluminescence study exhibits multiple traps with near-linear UV dose response, supporting dosimetric potential. The combined broad excitation, high emission intensity, and colour purity make the CaY2O4: Eu3+ a promising red phosphor for display and LED applications.

Advancements in material science have emphasized the upcycling of biodegradable matters for translational efficiency. Herein, we synthesized carbon quantum dots (CQDs) from biodegradable precursors, exhibiting sharp UV-vis absorption and reduced bandgap of 3.93 eV compared to the starting materials. These particles are amorphous with graphitic features, uniform dispersion, and nanometric roughness. They show excitationdependent photoluminescence across the visible light range, making them useful light-capturing probes. Application-wise, they serve as sensitive liquid-phase fluorescence sensors for Fe3+ and Cr3+ ions with 1.48 and 4.94 mu M LoD, respectively, which shows efficiency due to inclusion of arginine. Additionally, the CQDs display efficient photocatalytic degradation of rhodamine (91.66 % efficiency) and methylene blue (88.57 %), following pseudo-first-order kinetics. Biological assays reveals CQDs have optimal antibacterial activity against S. aureus and P. aeruginosa. The cytotoxicity assays reveal that CQDs have preferential action against HeLa cancer cell lines with an IC50 of 133.5 mu g/mL and prominent cytocompatibility with normal HEK-293 cell lines. Besides, the CQDs also confirm selective cellular uptake for HeLa cells and prove to have promising fluorescence labeling capabilities for in vitro studies. These findings indicate that CQDs have prominent applications as imaging probes, antibacterial activity, and industrial utility, such as ion sensing, and dye degradation.