Energy Transfer Mechanisms and Optical Thermometry of BaMgF₄:Yb³⁺,Er³⁺ Phosphor

Motivated from our previous studies on the upconversion properties of BaMgF₄:Yb³⁺,Tb³⁺ phosphor, here we investigated the upconversion properties of BaMgF₄:Yb³⁺,Er³⁺ phosphor. We demonstrate a two-way versatile approach for the fine-tuning of emission from green to the red region, by varying the dopant concentration and adjusting the pulse width of an infrared laser. The mechanism involved in tuning the emission color by laser power and pulse width variation was illustrated in detail. The temperature dependent upconversion spectra were studied by analyzing the fluorescence intensity ratio of the thermally coupled levels. The maximum sensitivity obtained is 83.29 × 10^-4 K^-1 at 583 K, which is much higher than the temperature sensitivity reported for other fluoride based materials. Moreover, the influence of the excitation power density on the ability of the phosphor for temperature sensing was also investigated. We obtained a maximum (∼415 K) temperature detection at 2563 mW laser power. The obtained results illustrate the potential use of BaMgF₄:Yb³⁺,Er³⁺ phosphor in an optical thermometer due to its highly sensitive temperature detection ability.