Mesoporous titania films are prepared via the polymer-template assisted sol-gel synthesis at low temperatures, using the titania precursor ethylene glycol-modified titanate (EGMT) and the diblock copolymer polystyrene-block-polyethyleneoxide (PS-b-PEO). UV-irradiation is chosen as a low temperature technique to remove the polymer template and thereby to obtain titania sponge-like nanostructures at processing temperatures below 100 °C. After different UV irradiation times, ranging for 0 h to 24 h, the surface and inner morphologies of the titania films are studied with scanning electron microscopy (SEM) and grazing incidence small-angle x-ray scattering (GISAXS), respectively. The evolution of the band gap energies is investigated using ultraviolet/visible (UV/Vis) spectroscopy. The findings reveal that 12 h UV-treatment is sufficient to remove the polymer template from the titania/PS-b-PEO composite films with a thickness of 80 nm, and the determined bad gap energies indicate an incomplete crystallization of the titania nanostructures.

The nanoscale miniaturization of hybrid organic-inorganic perovskite has given rise to new functionalities, but the full understanding of the multifaceted properties of perovskite nanostructures is still incomplete. Using a combination of optical and magnetic resonance (EPR) spectroscopies, we focused our investigation on the photoinduced electron transfer process taking place in perovskite nanocrystals blended with the fullerene derivative PCBM. In particular we analyzed the different effect of two types of nanocrystal ligands, namely octylamine and oleylamine, on the photoinduced processes. The electron transfer process resulted in efficient fluorescence quenching in a mixed solution and in the formation of charges (PCBM anions) detected by EPR in the blends. Both the optical and EPR techniques revealed a stronger effect when the shorter ligand is present. Finally, pulsed EPR demonstrated the stabilization of the photogenerated charges in proximity of perovskite nanocrystals.

In this study, we present the coupling between InAs submonolayer (SML) and stranski krastanov (SK) quantum dots (QDs). Interaction between these two different dot families has been manipulated by changing the capping layer thickness. Significant shift in photoluminescence (PL) peak is observed due to the coupling effect. The dynamics of the carriers in this mixed dot matrix has also been modified, which is evident from the increasing activation energy with increasing thickness of the capping layer. Moreover, an ex situ annealing study at different temperatures has been done to check the thermal stability of the as-grown samples. Annealing at lower temperatures, improves the crystal quality a bit, but higher annealing temperatures accelerate the In-Ga interdiffusion and form smaller dots, which is visible from a blue shift in the PL peak of annealed samples. Also, this thermal process improves the dot size distribution.

The impact of different annealing temperatures on the crystal structure, emission and radiative defects in ZnO nanocrystals (NCs) has been investigated by means of the scanning electron microscopy (SEM), Energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and photoluminescence (PL) techniques. ZnO NCs were prepared by the anodization of zinc sheets in an electrolyte and thermal annealed at the various temperatures: 200, 240, 280, 320, 360 and 400°C for two hours in ambient air. The XRD study indicates that ZnO NCs are characterized by the hexagonal wurtzite structure.

The study of annealing temperature impact on the morphology of ZnO NCs has shown that the NC size enlarges and the film crystallinity improves with increasing annealing temperatures from 200°C up to 400°C. But in the temperature range of 360-400oC the dissolution of oxygen atoms raises essentially in ZnO NC films as it follows from EDS data. Simultaneously, the near band edge (NBE) emission intensity falls down, XRD parameters of ZnO NCs change and the intensity of defect related orange and green PL bands increases owing to increasing the defect concentrations. The optimal temperatures for the ZnO NC oxidation, together with keeping the high NBE emission intensity, are estimated as 360 °C. The nature of native defects responsible for orange and green emissions in ZnO NCs has been discussed.

In this study the improvement in thermal stability of optical properties of InAs submonolayer quantum dot (SML QD) heterostructures is observed through incorporation of symmetric AlGaAs barrier layers. Low temperature photoluminescence (PL) spectra shows blue shift with less full width at half maxima, ascribe to the assimilation of AlGaAs barrier layers. The sample with confinement enhancing barrier shows the highest ground to ground transition energy with the lowest dot size distribution. Ex situ annealing of as grown samples, followed by PL analysis, confirms the improvement in thermal stability of optical behavior. For the samples with symmetric AlGaAs layer, annealing at higher temperatures under an inert condition can not change the downward transition energy effectively, whereas normal DWELL structures exhibits significant blue shift for the same.

We have found that several nitrogen-related luminescence centers appear at 389 nm, 503 nm (H3 center), 575 nm (NV0 center), 637 nm (NV- center) in single-crystalline Ib diamond cut by means of a YAG laser irradiation process, followed by a suitable hydrogen microwave-plasma treatment, and that cathodoluminescence peaks related to these centers substantially change in intensity by irradiating the sample with 15-keV electron beam (EB). The relative number of 389-nm centers originating from a pair of a substitutional nitrogen atom and an adjacent interstitial carbon atom increased while the concentrations of the vacancy-related centers were reduced with increasing 15-keV EB doses. These facts indicate that both the process-induced self-interstitials and the vacancies in the diamond rather easily moved to more preferential positions to form their stabler defect states, being suggestive of possibility to control densities of NV and NV-related centers.