Enhancement of Vibrant Up-Conversion in (Ca,Sr)F2:Er,Yb,Al Phosphors via Energy Transfer, Localized Interstitial Distortion, and Au Nanostructures

A remarkable increase in the luminescent intensity of Er³⁺-doped CaF₂ up-conversion phosphors was achieved, showing an approximate enhancement of over 1100-fold. This enhancement was realized by incorporating Yb³⁺, Al³⁺, Sr²⁺, and gold nanospheres and nanorods. The substantial improvement in up-converting luminescence effectively enhances sensitivity and efficiency at low excitation power densities. The up-conversion phosphors, consisting of (Ca,Sr)F₂:Er,Yb,Al, were easily prepared using excess NH₄F flux at 950 °C for 30 min. The structural confirmation of interstitial Al³⁺ ions within the CaF₂ lattice was achieved through synchrotron powder X-ray powder diffraction. The significant enhancement of up-conversion emission and their mechanisms in the phosphors were vividly represented through energy transfer, interstitials and local distortions, and localized surface plasmon resonances when excited with a 980 nm diode laser.