Hydrothermal synthesis of anisotropic SrGe4O9:Yb3+/Er3+ nanorods and optimized upconversion luminescence for optical temperature sensing

Abstract

Anisotropic Yb³⁺/Er³⁺ co-doped SrGe₄O₉ nanorods were successfully prepared via a simple but highly effective hydrothermal method. The crystal structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Under the 980 nm LD excitation, the germanate nanorods showed strong upconversion luminescence derived from the emissions of Er³⁺ ions. The concentrations of Yb³⁺ and Er³⁺ were optimized for achieving the strongest upconversion luminescence. The optical thermometric ability based on the fluorescence intensity ratio (FIR) of the adjacent green emissions was evaluated. A maximum sensitivity of 0.0076 K⁻¹ was achieved at 523 K in 1 mol% Er³⁺ doped sample. The results demonstrated that the SrGe₄O₉:Yb³⁺/Er³⁺ nanorods are a potential anisotropic optical medium and good candidates for temperature sensing.