Efficient energy transfer was demonstrated in the SrF₂ : Eu²⁺, Pr³⁺ phosphor synthesized by the co-precipitation method. Results obtained with X-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray spectroscopy (XPS), photoluminescence (PL) and decay curves proposed the UV-Vis energy transfer process. The energy transfer process between the Eu²⁺ and Pr³⁺ ions in SrF₂ was investigated to evaluate the potential of the Eu²⁺ ion as a sensitizer for the Pr³⁺ ion. The results proposed that Eu²⁺ could be a good sensitizer for absorbing the UV photons and efficiently enhancing the Pr³⁺ emission intensity. The energy transfer process was effective until concentration quenching for the Pr³⁺ ions occurred. The concentration quenching was attributed to cross-relaxation between the Pr³⁺ ions.

SrF₂:Eu,Ce³⁺ nanophosphors were successfully synthesized by the hydrothermal method during down-shifting investigations for solar cell applications. The phosphors were characterized by X-ray diffraction (XRD), scanning Auger nanoprobe, time of flight-secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. XRD showed that the crystallite size calculated with Scherrer’s equation was in the nanometre scale. XPS confirmed the formation of the matrix and the presence of the dopants in the SrF₂ host. The PL of the nanophosphor samples were studied using different excitation sources. The phenomenon of energy transfer from Ce³⁺ to Eu²⁺ has been demonstrated.

The up-conversion (UC) and temperature sensing behaviours of Y₂O₃:Ho³⁺, Yb³⁺ phosphors were investigated. A series of Y₂O₃:Ho³⁺, Yb³⁺ phosphors were synthesized using a solution combustion method. The cubic structure of the Y₂O₃ with an Ia$\overline{3}$ space group was analysed by using X-ray powder diffraction. Scanning electron microscopy was conducted to study the surface morphologies of the UC phosphors. Under 980 nm excitation, the UC emissions of Ho³⁺ from the ⁵S₂ → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵S₂ → ⁵I₇ transitions were observed, which occurred through UC energy transfer (ET) processes. The Yb³⁺ ion concentration severely affected the UC emission. The sensing behaviour of the phosphor was investigated through the green (⁵F₄, ⁵S₂ → ⁵I₈) to red (⁵F₅ → ⁵I₈) fluorescence intensity ratio (FIR). The maximum absolute and relative sensitivity values of S_A = 0.08 K⁻¹ and S_R = 0.64% K⁻¹ were obtained. The results revealed that the prepared Y₂O₃:Ho³⁺, Yb³⁺ phosphor is suitable for optical sensing at high temperatures.