Optical Absorption, Emission, and Excitation Spectra of Eu2+in the Alkali Halides

The optical absorption, emission, and excitation spectra for the Eu 5+ ion in the alkali halides have been investigated at room temperature. It was found that the magnitude of the 10Dq splitting of the 4f 6 5d configuration into its t 2g and e g components caused by the cubic crystalline field follows the spectrochemical series in which the ordering of the halides appears to be determined by the magnitude of the contact interactions. The emission spectrum of the quenched samples consists in all cases of only one band whose peak position moves to shorter wavelengths as the lattice parameter increases within a given series. The excitation spectrum correlates quite well with the optical absorption and shows that the e g level decays to the t 2g from which the fluorescence originates.