Cathodoluminescence of Double Layers of Phosphor Particles

Abstract

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. Recently we have described an idea to enhance the efficiency of cathodoluminescence (CL) of phosphor particle layers by depositing one layer on top of another.1 Such an enhancement is to be expected when a high-voltage phosphor is deposited on top of a low-voltage phosphor. The difference between a high-and low-voltage phosphor is the light output at low electron beam energies: a low-voltage phosphor has a high luminance yield, whilst the luminance of a high-voltage phosphor is low. At higher voltages, however, the high-voltage phosphor has the greatest output. As primary electrons penetrate the phosphor they progressively lose energy until they can no longer excite the phosphor. When the top, high-voltage, layer is thin enough to allow electrons of sufficient energy (but not enough to excite the high energy one) to penetrate into the low-voltage phosphor layer enhancement of the luminance may be expected. We shall refer to this theory as the "penetration model".An application of electron penetration in double and multi layers of phosphors were so-called "penetrons": Penetration CRTs, in which the color of the cathodoluminescence could be tuned by changing the energy of the electron beam.2-4 The objective of the scientists who developed penetrons was to maximize the color gamut of the tubes; no attention was paid to enhancing the lumen output.If the energy of the electron beam is not high enough, the electrons do not pass through the top layer and there will be no enhancement of the luminance. This was the main reason that there was no observable increase of the lumen efficacy of a thin layer of nano-sized Y 2 O 3 :Eu particles on top of a ZnO: Zn layer using electron beam energies up to 5 Kv.1 Another reason was the charging of non-conducting Y 2 O 3 :Eu layers upon electron bombardment. In order to cope with the charging of phosphor layers the measuring method was modified. Recently we publi...

Cathodoluminescence and Photoluminescence of YPO4:Pr3+, Y2SiO5:Pr3+, YBO3:Pr3+, and YPO4:Bi3+

“…We have recently described a new way for determining the energy efficiency of powder layers of phosphors, in which ZnO was used as a reference to determine the "real" current that hits the phosphor. 15,16 Besides YPO 4 . We found for η of ZnO at 15 keV 5.4%, which is 23% lower than we found earlier.…”

“…Recently we have described a measuring method for determining the CL efficacy and energy efficiency of phosphor powders in the case of charging. 15,16 We have slightly modified this method for determining the energy efficiency of the above mentioned UV phosphors. (Merck, p.a.)…”

Cathodoluminescence of Nanocrystalline Y2O3:Eu3+with Various Eu3+Concentrations

“…2 The phosphors used in these published studies were spherical nanoparticles of Y 2 O 3 :Eu 3+ and micrometer sized ZnO:Zn particles. The spherical nanoparticles of Y 2 O 3 :Eu 3+ were not monodisperse, because they consisted of a mixture of various batches.…”

“…[13][14][15][16][17][18][19] In the earlier studies [4][5][6][7][8][9][10][11][12] the focus was on the interpretation of the excitation and emission spectra in terms of energy transfer in the Y 2 O 3 :Eu 3+ crystals, whereas in the latter studies [13][14][15][16][17][18][19] the attention shifted toward the synthesis of nanomaterials. Most studies used photoluminescence (PL) techniques, [4][5][6][7] which enabled the excitation of energy levels having a particular symmetry and yielded insight on the energy flow in Y 2 were limited to the evaluation of the luminous efficiency. [10][11][12] A detailed investigation of the energy flow in Y 2 O 3 :Eu 3+ after excitation by an electron beam was performed by Klaassen et al 8 These authors also studied saturation effects in Y 2 O 3 :Eu 3+ at high current densities in an electron microscope.…”

“…This selection is not trivial, because many peaks in the spectrum of Y 2 O 3 :Eu 3+ suffer from overlap or are combinations of more than one spectral transition. 5,6 The first phase in the energy flow in Y 2 4,20 In Y 2 O 3 there are two different Y 3+ lattice sites, which possess the point symmetries C 2 and S 6 (Schoenflies notation): 24 lattice sites have C 2 symmetry, while the other 8 have S 6 symmetry. Both sites are six coordinate and are thus present in the ratio of 3:1.…”