Enhanced Green Emission of Eu 2+ by Energy Transfer from the 5 D 3 Level of Tb 3+ in NaCaPO 4

Eu 2+ /Tb 3+ single-doped and codoped NaCaPO 4 phosphors were prepared by a high-temperature solid-state reaction method. Their VUV–UV excitation spectra, emission spectra, fluorescence decay spectra, X-ray excited luminescence (XEL), and cathodoluminescence (CL) spectra were investigated and discussed. The main parameters of the electron–vibrational coupling between the Eu 2+ 5d states and host lattice vibrations (such as Huang–Rhys factor, effective phonon energy, and position of the zero-phonon line of the 4f 6 5d–4f 7 emission of Eu 2+ ) were estimated from the experimental spectra. For codoped samples NaCaPO 4:Eu 2+, Tb 3+, enhanced green emission of Eu 2+ by energy transfer (ET) from the 5 D 3 level of Tb 3+ was found.