R. Martínez-Martínez

Blue–green–red luminescence from CeCl3- and MnCl2-doped hafnium oxide layers prepared by ultrasonic spray pyrolysis

Hafnium oxide films doped with CeCl3 and/or MnCl2, and deposited at 300 °C by an ultrasonic spray pyrolysis process, were characterized using x-ray diffraction (XRD), energy-dispersive spectroscopy and photoluminescence. The XRD results revealed that the films are predominantly amorphous. The weak green–red emission of Mn2+ is enhanced through an efficient energy transfer from Ce3+ to Mn2+ ions. Spectroscopic data revealed that the energy transfer is nonradiative in nature and it could occur in Ce3+ and Mn2+ clusters through a short-range interaction mechanism. The efficiency of this transfer increases with the Mn2+ ion concentration, so that an efficiency of about 78% is attained for a 5 at.% of MnCl2 concentration, which makes these films interesting phosphors for the design of luminescent layers with blue, green and red emissions.

Ultrasonic spray-pyrolyzed CuCrO2 thin films

In this paper the optical, structural and electrical properties of CuCrO2 thin films deposited by ultrasonic spray pyrolysis at temperatures from 400 to 600 °C in steps of 50 °C are presented. Copper and chromium acetylacetonates were chosen as sources of Cu and Cr, respectively, and N,N-dimethylformamide was used as the solvent. X-ray results confirmed that the films as deposited showed the CuCrO2 phase without any post-deposition thermal annealing. The surface morphology was observed to be mirror like, and as the films were deposited at different temperatures, they gradually revealed the presence of small crystallites. The best films optical percentage transmission (in the visible region), about 58%, was obtained in films deposited at 450 °C, and the highest band gap energy (3.17 eV) was measured in films deposited at 400 °C. The electrical properties of the films were obtained by the Hall effect. A hole concentration in the range 1019–1021 cm−3, conductivity as high as 35 S cm−1, and mobility lower than 1 cm2 V−1 s−1 were obtained in the films. p-type conductivity was confirmed using the hot point probe arrangement, and the Seebeck coefficient was estimated. The hole conductivity is thought to be due to excess oxygen in the films. Finally, the minimum energy required to transfer carriers from acceptor level to the valence band in the films was estimated by impedance spectroscopy.

White Light Generation in Rare-Earth-Doped Amorphous Films Produced by Ultrasonic Spray Pyrolysis

Aluminium and hafnium oxide films doped with CeCl3/TbCl3/MnCl2 were deposited at 300 °C by ultrasonic spray pyrolysis. The films analysed by X-Ray diffraction exhibit a very broad band typical of amorphous materials. Non-radiative energy transfer from Ce3+ to Tb3+ and Mn2+ is observed upon UV excitation at 280 nm (peak emission wavelength of AlGaN-based LEDs). Such energy transfer gives place to a simultaneous emission of the donor and acceptor ions in the blue, green, yellow and red regions, resulting in cold white light emission, with chromaticity coordinates and colour temperatures: (0.30,0.32) and 7300 K (AOCTM film), and (0.32,0.37) and 6400 K (HOCTM film). Thus, this type of thin films might contribute to the development of efficient AlGaN-based LEDs pumped phosphors for cold white light generation.

Structural and Morphological Properties of Nanostructured ZnO Particles Grown by Ultrasonic Spray Pyrolysis Method with Horizontal Furnace

ZnO nanoparticles were synthesized in a horizontal furnace at 500°C using different zinc nitrate hexahydrate concentrations (0.01 and 0.1 M) as reactive solution by ultrasonic spray pyrolysis method. The physical-chemical properties of synthesized ZnO nanoparticles have been characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high resolution transmission electron microscopy (HRTEM). With the TGA is has optimized the temperature at which the initial reactive (Zn(NO3)2·6H2O), is decomposed completely to give way to its corresponding oxide, ZnO. SEM revealed secondary particles with a quasispherical shape that do not change significantly with the increasing of precursor solution concentration as well as some content of the broken spheres. Increasing the precursor solution concentration leads to the increase in the average size of ZnO secondary particles from to nm; XRD reveals the similar tendency for the crystallite size which changes from to nm. HRTEM implies that the secondary particles are with hierarchical structure composed of primary nanosized subunits. These results showed that the precursor concentration plays an important role in the evolution on the size, stoichiometry, and morphology of ZnO nanoparticles.