Enhancing temperature sensing behavior of NaLuF₄:Yb³⁺/Er³ via incorporation of Mn²⁺ ions resulting in a closed energy transfer

A strategy to improve the sensitivity of NaLuF₄:Yb³⁺/Er³⁺ is elaborated via incorporation Mn²⁺ ions, which results a closed energy transfer between Er³⁺ and Mn²⁺ ions (⁴S_3/2 (Er³⁺) → ⁴T₁ (Mn²⁺) → ⁴F_9/2 (Er³⁺)). The NaLuF₄:Yb³⁺/Er³⁺ and NaLuF₄:Yb³⁺/Er³⁺/Mn²⁺ phosphors are prepared by a hydrothermal method. Notably, incorporation Mn²⁺ for NaLuF₄:Yb³⁺/Er³⁺ phosphor rusults in enhancing the red to green intensity ratio, which acts as a bridge for energy transfer between ⁴S_3/2 and ⁴F_9/2 levels of Er³⁺. The temperature sensing behaviors of two phosphors are investigated in the 295–595 K range using a ratiometric technique under 980 nm excitation. Based on thermally (²H_11/2 and ⁴S_3/2) and non-thermally (⁴F_9/2 and ⁴S_3/2) coupled levels of Er³⁺, the influences of this energy transfer are discussed in detail. The sensitivity of NaLuF₄:Yb³⁺/Er³⁺ doping with Mn²⁺ ions based on non-thermally coupled levels is much higher than that without Mn²⁺ ions based on both thermally and non-thermally coupled levels in the 295–525 K range. The maximum sensitivity is 10.99 × 10⁻³ K⁻¹ at 295 K for NaLuF₄:Yb³⁺/Er³⁺/Mn³⁺ phosphor. These meaning results indicate that incorporation Mn²⁺ ions in NaLuF₄:Yb³⁺/Er³⁺ phosphor is an effective method for enhancing sensitivity in the 295–525 K range.