Preparation and upconversion luminescence properties of SiO₂@Gd₂O₃:Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) core-shell microspheres

In order to solve the problem of high price and poor size controllability of rare earth doped upconversion luminescent materials, spherical SiO₂@Gd₂O₃:Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) core-shell upconversion luminescent materials were successfully synthesized by simple chemical precipitation method using low cost and easy to prepare SiO₂ microspheres as cores and uniformly coated with Gd₂O₃:Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) shells. XRD results show that the SiO₂@Gd(OH)CO₃:Yb³⁺, Ln³⁺ precursor is firstly obtained by the reaction of urea with rare earth ions, then the Gd(OH)CO₃:Yb³⁺, Ln³⁺ shell is further transformed into cubic phase Gd₂O₃:Yb³⁺, Ln³⁺ with good crystallinity after calcination at 800℃. SEM and size distribution images show that the prepared samples are ideal core-shell microspheres with uniform size, and the average diameter is about 580 nm. Under the excitation of 980 nm, SiO₂@Gd₂O₃:Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) core-shell microspheres exhibit red, blue and green emissions respectively, corresponding to the ⁴F_9/2→⁴I_15/2 transition of Er³⁺, the ¹G₄→³H₆ transition of Tm³⁺, and the ⁵S₂→⁵I₈ transition of Ho³⁺, which are consistent with the luminescence color region of chromaticity color coordinates, indicating that three color upconversion luminescence is successfully achieved by simply adjusting the doped rare-earth ion species in the shell of SiO₂@Gd₂O₃:Yb³⁺, Ln³⁺ core-shell microspheres.