No abstract

Free from scaling effect is highly desirable but yet challenging in lead-free BaTiO3 (denoted as BTO). In this work, we revisit the synthesis BTO nanocubes via hydrothermal route and provide an insight on the photoluminescence behavior of BTO nanocubes, whilst others focus on the reproducibility of BTO nanocubes. The crystallinity of the BTOs was enhanced when the as-synthesized powders underwent calcination at elevated temperatures (> 500 °C). A combination of X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images affirms that the BTO nanostructures evolved from cubic to tetragonal and changing from pseudo-ellipsoid to nanocube with {100} sharp facets. The tunable optical band gaps (3.18-2.74 eV), Urbach tails in UV-Vis absorption spectra and the enhanced intensity of photoluminescence at violet wavelength (433.7 nm) indicate the presence of localized state. In order to sort out the origin of the localized state, either stems from structural disorder or surface state, time-resolved photoluminescence was carried out. The long decay of the time-resolved photoluminescence (> 100 ns) proves the dominant involvement of self-trapped states. This in turn narrows the band gap, thus facilitates photoluminescence excitation.

In this work, BaTiO3 nanoparticles were synthesized through hydrothermal method. The powder obtained from the hydrothermal process (as-synthesized powder) was calcined at 1000 °C. The phase formation and morphology of the as-synthesized and calcined powders were studied using X-ray diffraction (XRD), thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyzer, and transmission electron microscope (TEM). The XRD data showed that the as-synthesized powder is partially amorphous. Upon calcining the powder at 1000 °C, highly crystalline BaTiO3 with tetragonal structure was obtained. As shown by TGA and DSC analysis, the precursor powder was completely transformed into BaTiO3 at 1000 °C. The presence of BaCO3 as an impurity phase in the powder is due to the lack of Ba2+ / Ti3+/4+. Transmission electron microscope images showed that the particle size of the as-synthesized powder increased after calcination due to crystal growth. In addition, nanocubes with the average size of around 11.66 nm were obtained as a result of the calcination compared to the ellipsoid like particles of the as-synthesized powder.

We analyze the influence of electron irradiation on the electroluminescence spectra of white light emitting diodes (LEDs) based on indium gallium nitride. Three different irradiation fluences, 9.90×10 15 , 1.32×10 16 and 1.98×10 16 cm -2 , are studied. For all 27 samples of LEDs of the commercially available models VAOL-5GWY4, VAOL-10GWY4 and OVL-3321, we observe a significant decrease in the emission light intensity after the irradiation. Degradation of the overall light intensity is believed to be due to irradiation-induced defects which act as nonradiative recombination centres. We also study the emission intensities and the central wavelengths of the LED samples subjected to electron irradiation under conditions of different injection currents. After irradiation with the fluence 1.98×10 16 cm -2 , the blue peak located at 453 nm experiences severe degradation, so that only the yellow luminescence at 590 nm remains. This yellow band is related to radiative transitions from donor bands to the levels associated with gallium vacancies.