Upconversion Photoluminescence Properties of Er3+-Doped Ca12Al14O33 Aluminate Ceramics.

A series of Er³⁺-doped Ca_12-xEr_xAl₁₄O₃₃ (C12A7) aluminate ceramics with upconversion (UC) photoluminescence were synthesized by the traditional solid-state reaction method. The effects of Er³⁺ content on the crystal structure and upconversion photoluminescence properties were systematically studied. A portion of the Er³⁺ ions enter the host lattice sites of C12A7 by substituting the Ca²⁺ ions, and other Er³⁺ ions may exist interstitially when the content of Er³⁺ 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 Er³⁺ 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 Er³⁺. This variation trend in the intensities of the UC emission is consistent with that of the absorption cross-section (σ_abs) of Er³⁺ ions. The ultraviolet–visible–near-infrared absorption measurements and x-ray diffraction (XRD) results reveal that the Er³⁺ content determines the ratio of Er³⁺ 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:Er³⁺ are good UC candidate materials and help us better understand the UC photoluminescence properties of aluminate ceramics which have rarely been studied to date. [ABSTRACT FROM AUTHOR]