Adrian Camenzind

Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles

Cubic and/or monoclinic Y2O3:Eu3+ nanoparticles (10–50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700–1300°C for 10 h) as-prepared, initially monoclinic Y2O3:Eu3+ nanoparticles resulting in larger 0.025–1 μm, cubic Y2O3:Eu3+. The influence of europium (Eu3+) content (1–10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y2O3:Eu3+ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y2O3 particles at 900, 1100 and 1300°C for 10 h, the PL intensity increased as particle size increased and finally (at 1300°C) showed similar PL intensity as that of commercially available, bulk Y2O3:Eu3+ (5 μm particle size). Eu doping stabilized the monoclinic Y2O3 and shifted the monoclinic to cubic transition towards higher temperatures.

Flame aerosol deposition of Y2O3:Eu nanophosphor screens and their photoluminescent performance

Screens of Y(2)O(3):Eu(3+)-nanophosphor (d(BET) = 24 nm) with coating densities in the range 0.23-3.8 mg cm(-2) were obtained by flame aerosol deposition (FAD) from nitrate-based precursors. The average deposition rate was 0.22 mg cm(-2) min(-1). Porosity of the obtained deposits was 0.973 +/- 0.004. Light scattering of the coatings in the visible range showed a Rayleigh-like dependence on wavelength and, in comparison to the screens made of the commercial micrometer-sized phosphor powder (d(SEM) = 4 microm), was reduced by up to two orders of magnitude. As a result, the nanophosphor coatings maintained nearly constant brightness in a very wide range of coating densities. Furthermore, it should be expected that a substantially improved screen resolution can be achieved with such screens. For excitation at a wavelength of 254 nm, the maximum brightness of the FAD-deposited (Y(0.92)Eu(0.08))(2)O(3) phosphor screens in the transmission mode was nearly one third of that of the screens made of the commercial phosphor. It was demonstrated that light reflection from the supporting substrate and porosity of the coating significantly influence its photoluminescent performance.

High Performance Ethanol Sensor for Control Drunken Driving Based on Flame-made ZnO Nanoparticles

ZnO nanoparticles were produced by FSP using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The phase and crystallite size were analyzed by X-ray diffraction (XRD), and the specific surface area (SSA) of the nanoparticles was measured by nitrogen adsorption (BET analysis). The ZnO particle size and morphologies was further investigated by transmission electron microscopy (TEM) revealing spheroidal, hexagonal, and rod-like morphologies. The crystallite sizes of ZnO spheroidal and hexagonal particles were in the range of 10-20 nm. ZnO nanorods were found to be ranging from 10-20 nm in width and 20-50 nm in length. Sensing films were produced by mixing the particles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed onto Al2O3 substrates interdigitated with Au electrodes. The morphology of the sensing films was analyzed by scanning electron microscopy (SEM). The gas sensing of ethanol (25-250 ppm) was studied at 400 degC in dry air. The oxidation of ethanol on the surface of the semiconductor was confirmed by mass spectroscopy (MS). Thick (5 mum) ZnO films showed high sensitivity and fast response times (within seconds). The sensitivity increased and the response time decreased with increasing ethanol concentration. These concentrations (25-250 ppm) were corresponded to be almost in the same range with detection limit of concentration for human breath analyzer. These sensor can be performed an ethanol sensing device that could be employed for control of drunken driving.