Cathodoluminescence of Double Layers of Phosphor Particles

We present radiance measurements of particle layers of ZnO:Zn, Y 2 O 3 :Eu and Y 2 O 2 S:Eu bombarded with electrons at anode voltages between 1 and 15 kV. The layers described in this work refer to single component layers, double layers and two component mixtures. The phosphor layers are deposited on ITO-coated glass slides by settling; the efficiency of the cathodoluminescence is determined by summing the radiances and luminances in the reflected and transmitted modes respectively. The efficiency of a double layer of Y 2 O 3 :Eu on top of ZnO:Zn at high electron energy is significantly larger than the efficiency of a corresponding layer in which the two components are mixed. This result is interpreted in terms of the penetration-model, which predicts a larger efficiency for a high-voltage phosphor on top of a low-voltage phosphor. When a layer of the low-voltage phosphor ZnO:Zn is on top of the high-voltage phosphor Y 2 O 3 :Eu, we also observe a higher efficiency than that of the corresponding layer with both components mixed. In this case the efficiency increases due to suppression of charging in the Y 2 O 3 :Eu layer. Double layers of ZnO:Zn and Y 2 O 2 S:Eu did not show enhanced efficiency, because the size of the Y 2 O 2 S:Eu particles was too large to evoke the penetration effect.