Model representing growth mechanism in the LB thin film during phase transformation from α- to β-phase on annealing.

A systematic investigation on the proper utilization of defect levels present in ZnO is very much in demand to avail many applications of photonics in visible and near infrared (NIR) regions. In this paper, we have engineered intrinsic defects of zinc oxide (ZnO) to achieve high-quality intense whispering gallery modes (WGMs) in a single ZnO microsphere optical resonator by doping with alkali metal ions. Here, a single microsphere of undoped and doped ZnO was considered to investigate WGMs by recording luminescence spectra using a microphotoluminescence system under green laser excitation having a central wavelength of 532 nm and a fixed power of 55 mW/cm2. We have found that there is a significant enhancement in the intensity of WGMs in the case of doped ZnO in comparison to undoped ones. Among all the doped ZnO microspheres, 2 mol. % Li-doped ZnO yields the strongest and intense WGMs, which are accompanied by high-quality (Q)-factors. Furthermore, the pump power dependence measurement performed in 2 mol. % Li-doped ZnO reveals the lasing action in the visible optical window by explicitly exploiting the defect levels present in the material. Thus, our proposed defect engineered ZnO microsphere may represent a promising optical microresonator for developing highly sensitive WGMs based optical sensors.

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The charge transfer mechanism of a single bacterial cell with graphene oxide nanohybrids was measured using KPFM.

The UV-Vis absorption spectroscopy analysis reveals that prominent J-aggregation of ZnPc molecules was observed in the LB films while no such aggregation was found in the solution. Change in fluorescence color of ZnPc LB film from its solution confirms the appearance of new aggregation.