Synthesis and up-conversion luminescence properties of BaFBr-Er3+@SiO2 core/shell heterostructures

BaFBr:Er3+@SiO2 core-shell composites were synthesized starting from BaFBr:Er3+ phosphor core grains (BaFBr doped with 1 at% Er3+) prepared by coprecipitation method. A sol-gel process was used to obtain the outer SiO2 layer shell from silica sol precursor. The polycrystalline BaFBr:Er3+@SiO2 heterostructures were formed following calcination at 700 °C, in air. The resulting material was characterized in terms of microstructure, photoluminescence and up-conversion luminescence properties. The results indicate that the as-obtained composite has a core-shell structure and shows good luminescence properties. The BaFBr:Er3+@SiO2 heterostructure is made of BaFBr:Er3+ square sheets encased in a SiO2 shell layer with thickness values between 100 and 400 nm. Under 810 nm laser light pumping, the core-shell heterostructure exhibits Er3+ green up-conversion luminescence bands ((2H11/2, 4S3/2) → 4I15/2) at 525 and 545 nm, ascribed to a two-photon process.