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A gas-phase synthesis route based on spray pyrolysis with a residence/heating time of less than 0.1 s was designed to directly prepare Eu-doped Y2O3 phosphor nanoparticles. The average size of the phosphor particles decreased from the submicron size to around 10 nm when the concentration of the starting solution was increased. By increasing the operating temperature, from 1500 to 1700 °C, the submicron-particles were converted into a nano-particle phosphor, and their photoluminescence intensities at 611 nm (254-nm excitation) were greatly improved. This synthesis procedure has considerable potential for preparing a variety of doped luminescent nanoparticles without the need for post-treatment processing.

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Indium tin oxide particles were prepared using three different spray synthetic techniques: conventional, salt-assisted, and low pressure. Optimum conditions for the preparation of small size, nonagglomerated particles were investigated for these three methods. The use of the conventional spray pyrolysis method resulted in only larger particles (submicrometer order). Salt-assisted spray pyrolysis (SASP) and low-pressure spray pyrolysis (LPSP) produced highly crystalline, dense, homogeneous, and nearly nonagglomerated nanoparticles that were less than 25 nm in size. The size of the particles was in the range 12–24 nm for the SASP method and 8–14 nm for the LPSP method. In addition, the LPSP method led to the production of single nanometer-size multicomponent particles in a single step with less heating time without the need for any post heat treatment and additives.

Optimum conditions for the synthesis of nonagglomerated BaTiO 3 particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO 3 was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO 3 particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO 3 crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO 3 (200-500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO 3 particles about 20 nm in diameter.