Upconversion Photoluminescence Properties of Er3+-Doped Ca12Al14O33 Aluminate Ceramics

A series of Er 3+ -doped Ca 12- x Er x Al 14 O 33 (C12A7) aluminate ceramics with upconversion (UC) photoluminescence were synthesized by the traditional solid-state reaction method. The effects of Er 3+ content on the crystal structure and upconversion photoluminescence properties were systematically studied. A portion of the Er 3+ ions enter the host lattice sites of C12A7 by substituting the Ca 2+ ions, and other Er 3+ ions may exist interstitially when the content of Er 3+ ions is high. Under 980 nm laser excitation, all samples show two green emissions at 525 nm and 550 nm together with a red emission at 670 nm. With increased Er 3+ doping, both the green and red emission intensities increase monotonically and reach a maximum at x = 0.7, then decrease with further doping of the Er 3+ . This variation trend in the intensities of the UC emission is consistent with that of the absorption cross-section ( σ abs ) of Er 3+ ions. The ultraviolet–visible–near-infrared absorption measurements and x-ray diffraction (XRD) results reveal that the Er 3+ content determines the ratio of Er 3+ ions in isolated and cluster sites, respectively, which is responsible for the σ abs and the possibility of a cross-relaxation process. These results demonstrate that C12A7:Er 3+ are good UC candidate materials and help us better understand the UC photoluminescence properties of aluminate ceramics which have rarely been studied to date.