In principle all atoms in a finite solid are in a surface region. However the precision of measurement of many "bulk" parameters is such that the effects of the surface are below the limit of detection if thickness of the solid is more than a few tens of microns. Hence the effective surface region in practice is from a few atomic layers to several microns. (For insulators

the field from a surface charge can penetrate up to a few centimeters

[1]

.) As we know

the mean particle size of powder DCEL phosphors is about 1-3μm. Therefore the surface effect on DCEL devices must be Very obvious. But there is no report on it up to now. In this work

Thermally Stimulated Current(TSC) method was used to study the surface state levels of DCEL panels

and two surface electron-trap levels were measured for the first time.