A structural evaluation of ZnS-based electroluminescent phosphors and devices: a comparison with performance

Studies on the Orientation of ACEL ZnS:Cu Particles in Applied AC Fields

“…Also lines (or streaks) of emitted light in our case parallel to the fault planes are observed in some crystals in Figures 4, 5 and 6 (particularly the latter which shows two crystals under higher magnification), possibly explaining the "streaks" of light observed by others in previous studies. [12][13][14][15][16]24,27 A FESEM micrograph is presented in Figure 4d of the phosphor particles shown in the previous optical images in Figure 4a to 4c, the exact orientation of all particles is now clearly revealed. The brightest ACEL emitting particles (see Figure 4c) are shown to be oriented with cubic [111] axis at various angles, generally in a perpendicular direction to the applied alternating electric field that radiates across the gap between conducting tracks.…”

“…This is an important point and explains findings by other workers who observed that a number of particles are non-emitting. 24 The use of hydrochloric acid etched phosphor particles would have been of great assistance to the previous study.…”

“…The optical images show that the prominent linear streaks of light are formed of individual points of light, of which one point appears to be the brightest with a successive tailing off of light intensity along the streak, this detail probably appeared as the comets described in other studies. [12][13][14][15][16]24,27 The linear streaks of light are shown against a background of dimmer light that is composed of numerous points of light forming small groups with varying intensities. When comparing the FESEM images it is clear that these linear streaks of light appear to originate from elongated etched incisions along the planar stacking faults.…”

“…The flat expanse of rounded structures is also a new type of feature. Of particular relevance to the reported ACEL light emissions being in the form of spots or linear streaks of spots, [17][18][19]24,27 it is apparent from the FESEM images in Figures 7a and 7b that where an exposed face of the (111) plane is first attacked by the sulphuric acid it appears to first form faults across its surface (almost like the layers seen on the hydrochloric acid etch particles) but not the same as they are now in the (111) plane face. These are superimposed with evenly spaced circular protrusions (or spots) of material running along the length of the fault.…”

“…8,[13][14][15][16][17] Low magnification optical microscope studies reveal that commercial ACEL panels when excited with an electric field have a speckled appearance, the particles have a diameter between 10 to 50 micrometers are observed to emit with different intensities independent of particle size. 24 A number of particles in all ACEL panels do not display electroluminescence. When the phosphor layer in ACEL panels is excited with 366 nm light all the particles are observed to emit light with equal intensity.…”