Adhesion of Colloidal ZnO Particles on ZnS-Type Phosphor Surfaces

Abstract

Chemical and physical aspects of the adhesion of colloidal ZnO particles (d(50)=81 nm) on the surface of ZnS-type phosphors have been studied. Here, the green-emitting phosphor ZnS:Cu,Al,Cu (d(50)=5.0 µm) applied in TV screens was chosen as model compound. The ZnS material was pretreated in various ways (H(2)O, HCl, H(2)O(2)) and reacted thereafter with a suspension containing colloidal ZnO particles. Analytical investigations (SEM, ESCA) have shown that the adhesion of colloidal ZnO particles is strongly affected by the degree of hydrolysis of the ZnS surface. Electroacoustic investigations (ESA) prove that both types of surfaces, hydrolyzed ZnS as well as colloidal ZnO, are positively charged. Even so, adhesion of ZnO particles is encouraged very much under these conditions, indicating that secondary attractive forces (electrostatic interaction, chemical bonding) determine the amount of colloidal ZnO adhered on a ZnS-type phosphor. Copyright 2000 Academic Press.

Adhesion of Colloidal SiO2 Particles on ZnS-Type Phosphor Surfaces

“…However, former investigations give evidence for the fact that the distribution of ZnO on a ZnS surface itself can differ to a large extent. Coverage with colloidal ZnO particles leads to a very homogeneous distributions (11). In contrast, a brief H 2 O 2 treatment results in an inhomogeneous distribution because the hydrolysis starts at reactive surface sites such as edges of or voids between ZnS particles.…”

“…Previous studies have shown that the ZnO contamination can be removed by treating the ZnS material with dilute acid. On the other hand, it is also possible to enhance the ZnO coverage by a H 2 O 2 treatment (11). In addition to ZnO, carbon is also detected on the surface of the raw ZnS material.…”

“…Preparation of colloidal ZnO particles was described elsewhere (11,12). The average size of the particles was determined applying laser diffraction methods (Coulter Multisizer) to be 81 nm (d 50 ).…”

“…We have studied the system ZnS-ZnO-SiO 2 in more detail in order to gain greater insight into the functionality of the individual compounds (11). The green emitting phosphor ZnS:Cu,Al,Au was chosen as a carrier and can be assumed to be representative for ZnS-type phosphors in general.…”

Changes in the moisture stability of CaS:Eu2+ phosphors with surface coating methods

“…[10][11][12][13][14][15][16] Various alkaline earth sulfides with rare earth ion activators exhibiting performance advantages over the CaS:Eu 2+ red phosphors have been introduced. However, the application of alkaline earth sulfides has been limited by their instability.…”