We present a simple method to measure the cathodoluminescence of charging and non-charging phosphor powder layers at low primary electron beam energy. The method is based on comparing a non-charging surface of a conducting material such as copper or indium tin oxide with charging surfaces of non-conducting phosphors. The phosphors that were investigated were ZnO:Zn, which is slightly conductive and supposed not to charge upon electron bombardment, and Y 2 O 3 :Eu, which charges at sufficiently high current density. It was found that the luminous efficacies of ZnO:Zn and Y 2 O 3 :Eu at 5 keV primary beam energy were 23 and 16 lm/w respectively, larger than reported in the literature. This is partly explained by calculating the efficacy from the summation of the luminances measured in the reflected and transmitted mode. This method also minimizes the inaccuracy introduced by the effect of the coating weight. The ratio between luminances measured in reflection and transmission is described in terms of a one-dimensional light scattering theory. Previously we have reported on the various intrinsic luminescent phenomena, such as cathodoluminescence (CL), photoluminescence (PL) of nanometer sized rare earth doped yttrium oxide particles, crystallites and periodic nanostructures for photonic bandgap studies. 1-5More recently we have given an account on a CL study on double layers of zinc doped zinc oxide (ZnO:Zn) and nanometer sized (NS) europium doped yttrium oxide particles (Y 2 O 3 :Eu). 6 The objective of that study was to increase the light output of phosphor layers by making double layers of low and high voltage phosphors. In that study it was not possible to show that this approach was successful, mainly because the penetration depth at 5 kV in a thin top layer was insufficient to excite the bottom layer. Other problems were charging of the NS Y 2 O 3 :Eu top layer, which led to non-reproducible results and focusing effects of the electron beam. In this paper a new method will be introduced for determining the CL efficacy of phosphor powder layers that may charge upon electron bombardment. Furthermore, the optical behavior of the micrometer sized ZnO:Zn and the NS Y 2 O 3 :Eu particles in terms of a one-dimensional light scattering theory will be described.The challenge of measuring the CL of insulating phosphor layers at low electron beam energy is that the use of a top layer of aluminum (Al) to prevent charging of the phosphor grains cannot be used. This charging is negative in the case of the secondary emission coefficient γ being <1, or positive in the case that γ > 1. In principle the surface potential could approach that of the primary beam, and deflect the incoming beam. In practice no evidence of this happening has been observed in this work. What appears to be happening is that the thin surface layer charges up until it reaches the dielectric breakdown threshold of the material and then discharges, before resuming charging. As a result the surface potential fluctuates rapidly. This behavior can clearly b...

Herein a study on the preparation and cathodoluminescence of monosized spherical nanoparticles of Y2O3:Eu3+ having a Eu3+ concentration that varies between 0.01 and 10% is described. The luminous efficiency and decay time have been determined at low a current density, whereas cathodoluminescence-microscopy has been carried out at high current density, the latter led to substantial saturation of certain spectral transitions. A novel theory is presented to evaluate the critical distance for energy transfer from Eu3+ ions in S6 to Eu3+ ions in C2 sites. It was found that Y2O3:Eu3+ with 1-2% Eu3+ has the highest luminous efficiency of 16lm/w at 15keV electron energy. Decay times of the emission from 5D0 (C2) and 5D1 (C2) and 5D0 (S6) levels were determined. The difference in decay time from the 5D0 (C2) and 5D1 (C2) levels largely explained the observed phenomena in the cathodoluminescence-micrographs recorded with our field emission scanning electron microscope. . In this work CLtechniques were used as the characterization method of choice: in a vacuum system equipped with an electron gun and spectrometers, and in a field emission scanning electron microscope (FESEM). 3The application of Y 2 O 3 :Eu 3+ in cathode ray tubes has fostered extended luminescence studies of this material. Before 1996 these studies were focused mainly on micrometer sized particles, [4][5][6][7][8][9][10][11][12] more recently the attention has been directed to nano-sized powder materials. [13][14][15][16][17][18][19] In the earlier studies 4-12 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] concentration, energy can be transferred from S 6 states to C 2 states. At low Eu 3+ concentration there is no interaction between a Eu 3+ ion at a S 6 site and a Eu 3+ ion at a C 2 site respectively and thus, there will be no energy transfer. Energy transfer also occurs in phosphors that are excited by an electron beam; therefore, it was also an objective of this work to investigate what information concerning energy transfer can be obtained from CL-spectra that are generated without activation of specified energy levels.In concentration of ca. 4.7 mole %, efficient energy transfer occurs between the S 6 and C 2 sites for Eu 3+ in the 5 D 0 level. As the 5 D 0 level in the S 6 site is 87 cm −1 higher than the same level in the C 2 site, the efficient energy transfer from S 6 to C 2 sites presumably occurs by simultaneous creation of a phonon.22 This efficient energy transfer is necessary for the high emission efficiency of the Y 2 O 3 :Eu 3+ phosphor, as the 5 D 0 → 7 F 2 transition which gives rise to the red 611 nm emission is electric dipole allowed for Eu 3+ in C 2 sites but forbidden for Eu 3+ in S 6 sites. In this work it was decided to focus on the 5 D 0 → 7 F 1 (S 6 ) transition at 582 nm and the 5 D 0 → 7 F 2 (C 2 ) transition at 611 nm, because these are reasonably well separated from other trans...

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Highly stable field emission current densities of more than 6A∕cm2 along with scalable total field emission currents of ∼300μA per 70μm diameter carbon nanotube (CNT)-covered electron emitter dot are reported. Microwave-plasma chemical vapor deposition, along with a novel catalyst sandwich structure and postdepositional radio-frequency (rf) oxygen plasma treatment lead to well-structured vertically aligned CNTs with excellent and scalable emission properties. Scanning electron and transmission electron microscope investigations reveal that postdepositional treatment reduces not only the number but modifies the structure of the CNTs. Well-structured microwave-plasma-grown nanotubes become amorphous during rf oxygen plasma treatment and the measured work functions of CNTs change from 4.6eVto4.0eV before and after treatment, respectively. Our experiments outline a novel fabrication route for structured CNT arrays with improved and scalable field emission characteristics.

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