Designing of a white light emitting diode based on rare earth metal free intrinsic Zn-MOF by fabricating a suitable device.

This work for the first time unfurls the fundamental mechanisms and sets the stage for an approach to derive electrocatalytic activity, which is otherwise not possible, in a traditionally known wide band-gap oxide material. Specifically, we report on the tunable optical properties, in terms of wide spectral selectivity and red-shifted band gap, and electrocatalytic behavior of iron (Fe)-doped gallium oxide (β-Ga2O3) model system. X-ray diffraction (XRD) studies of sintered Ga2–x Fe x O3 (GFO) (0.0 ≤ x ≤ 0.3) compounds provide evidence for the Fe3+ substitution at Ga3+ site without any secondary phase formation. Rietveld refinement of XRD patterns reveals that the GFO compounds crystallize in monoclinic crystal symmetry with a C2/m space group. The electronic structure of the GFO compounds probed using X-ray photoelectron spectroscopy data reveals that at lower concentrations, Fe exhibits mixed chemical valence states (Fe3+, Fe2+), whereas single chemical valence state (Fe3+) is evident for higher Fe content (x = 0.20–0.30). The optical absorption spectra reveal a significant red shift in the optical band gap with Fe doping. The origin of the significant red shift even at low concentrations of Fe (x = 0.05) is attributed to the strong sp–d exchange interaction originated from the 3d5 electrons of Fe3+. The optical absorption edge observed at ≈450 nm with lower intensity is the characteristic of Fe-doped compounds associated with Fe3+–Fe3+ double-excitation process. Coupled with an optical band-gap red shift, electrocatalytic studies of GFO compounds reveal that, interestingly, Fe-doped Ga2O3 compound exhibits electrocatalytic activity in contrast to intrinsic Ga2O3. Fe-doped samples (GFO) demonstrated appreciable electrocatalytic activity toward the generation of H2 through electrocatalytic water splitting. An onset potential and Tafel slope of GFO compounds include ∼900 mV, ∼210 mV dec–1 (x = 0.15) and ∼1036 mV, ∼290 mV dec–1 (x = 0.30), respectively. The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms such as doping resulting in new catalytic centers, enhanced conductivity, and electron mobility. Hence, in this report, for the first time, we explored a new pathway; the electrocatalytic behavior of Fe-doped Ga2O3 resulted due to Fe chemical states and red shift in the optical band gap. The implications derived from this work may be applicable to a large class of compounds, and further options may be available to design functional materials for electrocatalytic energy production.

Fluorescent graphene quantum dots (GQDs) prepared from low-cost and sustainable precursors are highly desirable for various applications, including luminescence-based sensing, optoelectronics, and bioimaging. Among different natural precursors, the unique structural and compositional variety and the abundance of aromatic carbon in lignin make it a unique and renewable precursor for the green synthesis of advanced carbon-based materials including GQDs. However, the inferior photoluminescence quantum yield of GQDs prepared from natural precursors, including lignin, limits their practical utility. Here, for the first time, we demonstrate that the presence of heteroatoms in the innate structure of lignosulfonate can be leveraged to derive in situ heteroatom-doped GQDs with excellent photophysical properties. The as-synthesized lignosulfonate-derived GQDs showed compelling blue fluorescence with a high quantum yield of 23%, which is attributed to in situ S and N doping as confirmed by using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. Assisted by the in situ doping, we further engineered the lignosulfonate-derived GQDs by incorporating a metal atom dopant to derive an enhanced quantum yield of 31%, the highest for any lignin-derived GQDs. Moreover, fundamental photoluminescence studies reveal the presence of multiple emissive centers, with edge states acting as dominant emission centers. Finally, we also demonstrate the applicability of the luminescent, metal- and nonmetal-codoped lignin-derived GQDs as a highly selective sensor for the sub-nanomolar level detection of mercuric ions in water.

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