Low Power High Purity Red Upconversion Emission and Multiple Temperature Sensing Behaviors in Yb³⁺,Er³⁺ Codoped Gd₂O₃ Porous Nanorods

Lanthanide ion doped upconversion nanomaterials have attracted great interest because of their extensive application, especially in color display and temperature sensing. However, control synthesis of lanthanide ion doped upconversion nanomaterials with high color purity and excellent temperature sensing properties remain a great challenge. Herein, the first preparation of Yb³⁺,Er³⁺ codoped Gd₂O₃ porous nanorods not only achieve high purity red upconversion under low pump power but also possess superior temperature sensing performance. By utilizing a single NIR 980 nm laser, the high purity red and orange emission with high color purity of 99.7%, 99.6% are simultaneously realized under low power of 10 mW, respectively. Furthermore, excellent temperature sensing performing, integrating ultrahigh absolute sensitivity (S_a), outstanding relative sensitivity (S_r), and good signal discriminability (ΔE ≈ 1059 cm^–1) is implemented in single Gd₂O₃:Yb³⁺,Er³⁺ nanorods based on the fluorescence intensity ratio (FIR) technique from stark sublevels of Er³⁺ ions. Particularly, the maximum S_a and S_r of the thermally coupled level (TCL) pair by (G₁₊G₂)/G₄ is 1.86% (at 558 K) and 1.51% (at 298 K), which is superior to the sensitivity based on traditional TCL pair by stark levels of ²H_11/2/⁴S_3/2. Additionally, experimental results demonstrate that the values of S_a and S_r from the stark sublevels are proportional to energy spacing (ΔE), overcoming the dilemma between relative sensitivity and absolute sensitivity based on traditional TCL pairs. This work opens a new avenue toward constructing high purity emission and multiple temperature sensing performing materials.