Upconversion fluorescence spectroscopy of Er 3+ pairs in CsCdBr 3a

Abstract

Using a combination of optical absorption and laser selective excitation, an extensive set of energy levels has been established for the principal Er 3+ center in CsCdBr 3:Er 3+, and Er 3+ -vacancy-Er 3+ arrangement. The polarized absorption and fluorescence measurements indicate a pair center slightly distorted from the ion positions of the host crystal. This Er 3+ pair center exhibits strong upconversion fluorescence, with up to one third the intensity of direct fluorescence, giving an overall visual white emission under CW laser excitation of the 4I 15/2 → 4S 3/2 transitions in the green. Unusual aspects of the spectra are small pair splitting (about 0.5 cm -1) of the sharper absorption lines and shifts (about 0.3 cm -1) of the fluorescence lines between δ and π polarizations of the incident laser light.