Upconversion process in BaY₂ F₈ :Yb³⁺ ,Ho³⁺ phosphor for optical thermometry

A BaY₂ F₈ :Yb³⁺ ,Ho³⁺ phosphor was synthesized using a simple precipitation method. The temperature-sensing properties of BaY₂ F₈ :Yb³⁺ ,Ho³⁺ phosphor were investigated using the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (⁵ F₄ and ⁵ S₂ ) of Ho³⁺ . Energy transitions ⁵ F₄ →⁵ I₈ and ⁵ S₂ →⁵ I₈ gave rise to emission peaks at 538 nm and 549 nm, respectively. The areas under these two emission peaks were used to calculate the FIR. Temperature-dependent upconversion luminescence was recorded in the temperature range 303-623 K using a 980 nm laser excitation source. The results suggested that the BaY₂ F₈ :Yb³⁺ , Ho³⁺ phosphor has the potential to be used as a non-contact optical temperature sensor.