Morphological features of Y203:Eu particles obtained through twin fluid and ultrasonic atomization

Abstract

Modem display devices such as plasma display and field emission display employ advanced Eu-doped yttrium oxide material, a well-known red phosphor. Utilization in such devices requires particles with spherical shape, narrow size distribution and non-aggregation characteristics since this ensures high resolution and improved brightness. Spray pyrolysis is a feasible method for obtaining the needed phosphor particle characteristics in view of the fact that atomized precursor solution, when fed into furnace, leads to the successive solvent evaporation, drying, solute precipitation and chemical decomposition on a droplet level, ensuring the formation of particles with required compositional and structural characteristics. Atomization process can be established by two different principles: disintegration of liquid jet by an air flow in case of twin-fluid atomizers and by liquid sonication. The latter phenomenon occurs when a liquid is placed on a smooth surface that is set into vibrating motion perpendicular to the surface. When the amplitude of the underlying vibration increases to the critical value the generated standing waves start to collapse and tiny drops of liquid are ejected from the top of the degenerating waves normal to the atomizing surface. In this work yttrium oxide doped with 5 at% of europium was directly prepared by spray pyrolysis at 900°C and the effect of the type of atomization process on the morphology and the size of the particles was investigated by using RBI's ultrasonic atomizer (frequency 1.3 MHz) and a TSI 3079 Model twin-fluid atomizer. Under the frequency of 1.3 MHz generated droplets have the mean size around 3 urn. In general it is considered that droplets produced by ultrasonic atomization have a relatively narrow size distribution and smaller particle size than twin-fluid, but depending on the specific nozzle and the type of liquid delivery system employed in twin-fluid atomization submicronic droplets can be generated as well. The twin-fluid used in this work uses a compressed air atomizer with a stainless-steel twin-stream injection nozzle producing a polydisperse aerosol with a mean droplet diameter of 0.3 urn. Since the properties of advanced materials significantly depend on particle size, shape and morphology it is of great interest to find out the correlation between those characteristics and processing parameters. Detail characterization of produced powders was carried out by means of XRD, SEMIEDS and TEM analysis.