Byung-Chul Hong

Organic dye-doped thin films for wavelength conversion and their effects on the photovoltaic characteristics of CdS/CdTe solar cell

For the improvement of the conversion efficiency of CdS/CdTe solar cells by applying the wavelength conversion properties, the spectroscopic studies of the fluorescent laser dye Rhodamine 6G (Rh6G)-doped into polyvinylbutyral (PVB) and polymethylmethacrylate (PMMA) were carried out. It was found that all the photoluminescence excitation (PLE) spectra below 540 nm were effectively converted to photoluminescence (PL) spectra in the wavelength region above 550 nm where the solar cell possessed a high spectral quantum efficiency. The external quantum efficiencies of PVB:Rh6G and PMMA:Rh6G films were estimated to be 0.9±0.05 and 0.4±0.1, respectively. When the PVB:Rh6G film was placed on the top of the CdS/CdTe solar cell, both short-circuit current and conversion efficiency increased by 11% compared with the cell with no film.

Syntheses of Eu-activated alkaline earth fluoride MF2 (M = Ca, Sr) nanoparticles

The Eu2+ ion-activated CaF2 and SrF2 nanoparticles were prepared by the sol–gel technique assisted with the trifluoro-acetic acid (TFA), and were evaluated by X-ray diffraction (XRD), photoluminescence (PL), photoluminescence excitation (PLE) measurements and atomic force microscopy (AFM) observation. A modified reducing method based on the thermal-carbon reducing atmosphere (TCRA) treatment using activated carbon was proposed to realize the effective reduction from Eu3+ to Eu2+ ions, in which the nanoparticles showed a strong and broad luminescence due to the parity allowed 4f7–4f65d1 transition. From the XRD results, it was found that the average particle size proportionally increased in the range of 15 to 120 nm and 10 to 100 nm for CaF2 and SrF2, respectively, with increasing sintering temperatures 300–700 °C. The surface images of nanoparticles obtained by the AFM revealed that the grains with high uniformity grew with increasing TCRA temperatures. It was confirmed that the reduced Eu2+ ions were homogeneously dispersed with the critical distance 16–17 A in the fluoride nanoparticles from the concentration quenching results.

Development of Eu-Enhanced TiO2 Nanophotocatalyst for Effective Utilization of Spent Nuclear Fuel

A UV-photoactive Eu-doped TiO2 nanoparticle activated with its wavelength-matched nanoscintillator is proposed for the effective utilization of spent nuclear fuel. The Eu-doped TiO2 nanoparticles were synthesized by the alkoxide-based sol–gel method at various doping concentrations and sintering temperatures. The X-ray diffraction (XRD) spectra revealed that the existence of the anatase phase of TiO2, which is favorable for photocatalytic application, was extended up to 800 °C by Eu doping. The average crystallite size of 40 nm in the pure TiO2 sintered at 600 °C was decreased by 50% in the case of the 0.5 mol % Eu-doped one. The absorption edge obtained from UV–vis absorbance spectra yielded a slightly blue shift that gave a good agreement with the results of size suppression. The photocatalytic activities of nanoparticles were evaluated from the degradation of methylene blue (MB) solution under UV irradiation, and the optimum activity obtained for the 0.75 mol % Eu-doped TiO2 was three times higher than that of the pure TiO2.