Green luminescence and degradation of Ce3+ doped CaS nanocrystalline phosphors were studied with a 2 keV, 10 mu A electron beam in an O-2 environment. The nanophosphors were synthesized by the co-precipitation method. The samples were characterized using X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy/electron dispersive X-ray spectroscopy and Photoluminescence (PL) spectroscopy. Cubic CaS with an average particle size of 42 +/- 2 nm was obtained. PL emission was observed at 507 nm and a shoulder at 560 nm with an excitation wavelength of 460 nm. Auger electron spectroscopy and Cathodoluminescence (CL) were used to monitor the changes in the surface composition of the CaS:Ce3+ nanocrystalline phosphors during electron bombardment in an O-2 environment. The effect of different oxygen pressures ranging from 1 x 10(-8) to 1 x 10(-6) Torr on the CL intensity was also investigated. A CaSO4 layer was observed on the surface after the electron beam degradation. The CL intensity was found to decrease up to 30% of its original intensity at 1 x 10(-6) Torr oxygen pressure after an electron dose of 50 C/cm(2). The formation of oxygen defects during electron bombardment may also be responsible for the decrease in CL intensity. (C) 2009 Elsevier B.V. All rights reserved.