Coexistence of the Eu2+ and Eu3+ Centers in the CaO : Eu Powder Phosphor

Coexistence of the Eu2+ and Eu3+ centers is confirmed for two kinds of phosphors prepared in and by observing electron spin resonance (ESR) spectra, photoluminescence and optical excitation spectra and luminescence decay curves. The ESR signal intensity due to Eu2+ in prepared in was about 7 times that in prepared in . Details of the luminescence spectra of the Eu2+ centers in are reported. The emission band of is located at 733 nm at 300 K, and the emission and excitation bands exhibit phonon structures at low temperatures. The luminescence lifetime of the Eu2+ center is about 1 μs at 300 K.