Y₂O₂S:Eu Red Phosphor Powders Coated with Silica

Abstract

Y 2 O 2 S:Eu red phosphor powders were coated with silica (SiO 2 ), using sol-gel and heterocoagulation techniques. Phosphor powders were dispersed in ethanol with tetraethyl orthosilicate and water. Hydrochloric acid was used to catalyze the sol-gel reaction, and an amorphous film 10 -20 nm thick was observed via transmission electron microscopy (TEM). Colloidal SiO 2 powders 10 -70 nm in size were used, and the SiO 2 powder coating was made by controlling pH values in the range of 4.5-8, in which a negatively charged surface of SiO 2 powder and a positively charged surface of red phosphor powder were formed. Then, SiO 2 powders were adsorbed electrically onto the phosphor powder surface, as evidenced by TEM, dissolution, and zeta potential measurements. Chemical bonding in the coating was studied using electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy.

Vitreous phase coating on glaserite-type alkaline earth silicate blue phosphor BaCa2MgSi2O8:Eu2+

“…It is considered that the high chemical durability was achieved by the vitreous phase coating, as reported for other coated phosphors [21][22][23][24][25][26]. In the present study, added aluminum did not show an effective result.…”

“…However, in actual usage, phosphor materials are expected to have high chemical durability. In order to improve the durability, encapsulation of individual phosphors has been attempted by sol-gel process of tetraethyl orthosilicate (TEOS) and by heterocoagulation process of colloidal silica [21][22][23][24][25][26]. In the case of M 3 MgSi 2 O 8 orthosilicates, however, similar vitreous-phase coating can be formed by careful control of synthesis temperature since the M 3 MgSi 2 O 8 contains a typical glass network former SiO 2 as a constituent.…”

Effects of MgO coating on microstructure and dielectric properties of BaTiO3

“…There- * Corresponding author. fore, various chemical techniques such as sol-gel, 12,13 heterocoagulation [14][15][16] and homogeneous precipitation coating 17,18 have been proposed to maximize the homogeneous distribution of additives.…”

Effects of Oxide Additives Coating on Microstructure and Dielectric Properties of BaTiO3

“…Consequently, fired ceramics are physically and chemically inhomogeneous. Various chemical techniques such as sol-gel [1,2], hetero-coagulation [3][4][5] and homogeneous precipitation coating [6,7] have been proposed to maximize homogeneous distributions of additives. Such preparation techniques are advantageous in the manufacture of MLCC with thin dielectric layers having submicron grain sizes and high breakdown voltages.…”