Phosphors normally lose brightness upon bombardment with electron, ion or photon beams. A combination of techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and cathodoluminescence (CL) spectroscopy was used to show that the main reason for the degradation in luminescent intensity under electron bombardment is the formation of a non-luminescent layer on the surface due to an electron-stimulated surface chemical reaction (ESSCR). The decrease in luminance was found to be a result of the growth of the 'dead layer'. Different phosphors which include sulfide-based as well as oxide-based phosphors reacted similarly under electron bombardment. The formation of an altered layer (oxide layer) on the surface of the different phosphors leads to the decrease of the luminescent intensity at that specific wavelength and in some cases to an increase of the intensity at another wavelength. The mechanisms of the degradation of several rare earth and transition metal phosphors are discussed in detail.

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We report the effects of heat treatment on Zn x Ni 1−x Fe 2 O 4 (x = 0, 0.5 and 1.0) and MnFe 2 O 4 ferrite nanoparticles. The as-prepared compounds were sintered from 400 • C to 1100 • C. Pure ZnFe 2 O 4 (x = 1.0) and MnFe 2 O 4 could be obtained under low reaction temperature of 200 • C. NiFe 2 O 4 (x = 0) and Zn 0.5 Ni 0.5 Fe 2 O 4 (x = 0.5) nanoferrites crystallized with single phase cubic spinel structure after annealing at 600 • C. The single phase cubic spinel structure of these compounds was destroyed after annealing at temperature above 700 • C. The magnetization measurements indicate superparamagnetic behavior of the nanosized compounds produced.Keywords Spinel · Mössbauer spectroscopy · Nanoparticles Magnetic nanoparticles of spinel ferrites have wide applications in modern technologies such as drug delivery systems, medical diagnostics, magnetic resonance imaging contrast agents and magnetocarolic refrigeration [1, 2]. Superparamagnetism is a unique property of these nanoparticles and can be controlled by particle size. In the superparamagnetic state each nanoparticle has well defined magnetic order and behaves like a paramagnetic atom. The collective behavior of a system of magnetic nanoparticles is the same as that of a paramagnetic atom. Efforts are still being made to improve or develop synthesis techniques of magnetic nanoparticles. The magnetic properties of Zn-Ni ferrits have been studied previously [4][5][6]. Of interest are the effects of reaction temperature and sintering temperatures on single phase formation. In the present work, a wet chemical method known as glycolthermal method [3] has been used to produce Zn x Ni 1−x Fe 2 O 4 (x = 0, 0.5 and 1.0) and MnFe 2 O 4 nanoferrites.

The degradation of Gd2O2S:Tb phosphor was studied with Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL). The surface reactions were monitored with AES while the light output was measured with a PC2000‐UV spectrometer. The CL of the Gd2O2S:Tb was excited with a 2 keV energy electron beam with a beam current density of 26 mA/cm2. The CL and AES were measured simultaneously while the sample was bombarded with the electrons in an oxygen atmosphere. A comparison between the low energy peaks of the AES spectra before and after degradation showed significant differences in the shape of the different peaks. A linear least squares (LLS) method was applied to resolve the peaks. Elemental standards from Goodfellow were used in conjunction with the measured data to subtract the S and Gd peaks. A direct correlation between the surface reactions and the CL output was found. The CL decreased while the S was removed from the surface during electron bombardment. A new non‐luminescent surface layer that formed during electron bombardment was responsible for the degradation in light intensity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)