Following growth doping strategy and using dopant oxides nanocrystals as dopant sources, we report here two different transition-metal ions doped in a variety of group II-VI semiconductor nanocrystals. Using manganese oxide and copper oxide nanocrystals as corresponding dopant sources, intense photoluminescence emission over a wide range of wavelength has been observed for different host nanocrystals. Interestingly, this single doping strategy is successful in providing such highly emissive nanocrystals considered here, in contrast with the literature reports that would suggest synthesis strategies to be highly specific to the particular dopant, host, or both. We investigate and discuss the possible mechanism of the doping process, supporting the migration of dopant ions from dopant oxide nanocrystals to host nanocrystals as the most likely scenario. SECTION Nanoparticles and Nanostructures

Crystalline nanoparticles of anatase phase nitrogen-doped TiO2 (N–TiO2), boron and nitrogen codoped TiO2 (B–N–TiO2), and undoped TiO2 (TiO2) were synthesized by a facile xerogel method followed by reduction in a glycol medium to forcibly create Ti3+ ions (self-doping) in them (R–N–TiO2, R–B–N–TiO2, and R–TiO2, where R stands for reduced) and studied their photocatalytic activity for hydrogen generation from water. A clear red shift of the absorption edge and stronger absorption in the visible region was observed for both reduced and unreduced N–TiO2 and B–N–TiO2 compared to the other samples. The presence of bonded nitrogen in the N-doped samples was evidenced from their N1s X-ray photoelectron spectra. Photocatalytic activity for hydrogen generation using sunlight-type radiation showed enhanced activity for the reduced and doped samples compared to pristine TiO2. The enhanced photocatalytic activity of the R–N–TiO2 for hydrogen generation is attributed to the enhanced light absorption resulting from the narrowing of the band gap caused by the contribution of anion levels near the conduction band and 2p levels of N near the valence band of TiO2. A significant enhancement of photocatalytic activity was observed when Pd metal was present as a cocatalyst due to the efficient separation of photogenerated charge carriers in these nanoparticles.

This article presents the experimental and theoretical insights into defect-engineered MoO 2 nanostructures (NSs) in terms of oxygen vacancy and OH − occupancy toward oxygen evolution reaction (OER). Two categories of β-MoO 2 NSs are grown on a silicon substrate via a hydrogenation process from pregrown α-MoO 3 structures. The postgrown MoO 2 system gets OH − occupancy after 7 h of annealing (MoO 2+OH − ). On increasing the annealing duration to 9 hrs, both oxygen vacancies and OH − occupancy have been made into the MoO 2 system (MoO 2−x+OH − ). The as-grown materials have been assessed for promising energy conversion applications toward electrocatalytic OER. The as-grown MoO 2−x+OH − very efficiently catalyzes the OER at a lower overpotential and yields a higher current density compared to the as-grown MoO 2+OH − and commercial MoO 2 . Both the oxygen vacancy and OH − occupancy in the MoO 2 system play a synergistic role in enhancing the OER properties. The experimental observations are validated theoretically and plausibly explained with the help of a state-of-the-art density functional study. The simulation calculations reveal that the introduction of oxygen vacancy and OH − occupancy lowers the overpotential of OER. The OH − ions act passively on the surfaces of MoO 2 that decrease the binding of reaction intermediates and aid in easy desorption of O 2 molecules. Besides, the oxygen defect sites reduce the charge-transfer resistance, which eventually reduces the OER overpotential. Our empirical findings with theoretical supports render a significant shrewdness to the electrocatalytic performances of the defectengineering MoO 2 systems toward OER applications.

Defect engineering in flower-shaped iron-doped nickel selenide as an electroactive material for water oxidation reaction.

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