We report cavity enhanced periodic structures in cathode luminescence spectra in TiO2:Eu3+ microspheres ranging from 6.2 to 12.2 mu m in diameter. The spectral structures observed at the accelerating voltage below 10 kV are attributed to the lower order whispering galley modes, while the additional components appearing at 20 kV are to the higher order modes within the microsphere. These observations illustrate that the basic properties of phosphors can be advanced from the point of view of cavity quantum electrodynamics by fabricating a microcavity structure onto a single phosphor crystal. (c) 2006 American Institute of Physics.