Luminescent Er3+ centers in CaSc2O4:Er3+:Yb3+ upconversion phosphor

Highlights: • Luminescent Er³⁺ centers are identified in Er:Yb:CaSc₂O₄ at low temperature (10K). • Stark energy levels of Er³⁺ multiplets ⁴I_15/2, ⁴I_13/2, ⁴F_9/2, and ⁴S_3/2 are found. • Influence of the two centers on upconversion luminescence emission is discussed. • Influence of temperature on upconversion luminescence intensity and color is found. The structure of luminescent centers in the upconversion material Er:Yb:CaSc₂O₄ is investigated using high-resolution optical spectroscopy methods at low temperature (10K). Two luminescent centers were identified in Er(2 at%):CaSc₂O₄: one corresponding to Er³⁺ on Ca²⁺ positions (center I) and one corresponding to Er³⁺ on Sc³⁺ positions (center II). Both X-ray diffraction and optical spectroscopy indicate an increase in the population of center II with the increase of doping concentrations. The Stark energy levels corresponding to multiplets ⁴I_15/2, ⁴I_13/2, ⁴F_9/2 and ⁴S_3/2 were obtained for the two luminescent centers, using selectively-excited luminescence. Upconversion measurements performed at low temperatures (10K) showed that the contribution of center I is dominant. The temperature dependence of the upconversion intensity and of the red to green ratio is discussed.