Up-conversion luminescence performance and application of GdOF:Yb,Er porous spheres obtained by calcining NaGdF₄:Yb,Er microcrystals

Precise tuning of the structure, luminescence intensity, and color of lanthanides-doped up-conversion (UC) micro/nanomaterials is essential for many applications. Herein, a porous material with enhanced UC emission was achieved by calcining the hexagonal phase NaGdF₄:Yb,Er microrods synthesized by the hydrothermal method. Under excitation at 980 nm, compared to the as-synthesized NaGdF₄:Yb,Er microcrystal, the 700 ℃ calcined products exhibit a single-band red UC luminescence and nearly two orders of luminescence enhancement. However, the XRD patterns of the calcined products are simultaneously consistent with the cubic phase NaGdF₄ and rhombohedral phase GdOF, which makes the composition of calcined products be an open question. We have carefully designed and carried out some experiments, and then verified the GdOF identity of the calcined products. Interestingly, GdOF:Yb,Er porous spheres exhibit a greater loading capacity (0.25 g/g) of Cu-Cy photosensitizer than the as-synthesized NaGdF₄:Yb,Er (0.12 g/g) microcrystals. Furthermore, after loading the photosensitizer, GdOF:Yb,Er porous spheres still emit a strong single-band red luminescence upon 980 nm excitation. These phosphors can also be used as security inks for printing luminescent patterns. This study provides a novel way towards the preparation of the GdOF:Yb,Er porous phosphors with a tremendous potential in drug loading, anti-counterfeiting and imaging applications.