Impact of Sensitizer Yb³⁺ on Structural and Optical Properties of AE₂SiO₄ (AE = Ba, Ca, Sr) Orthosilicates

In the present work, BaSrSiO₄: Yb and CaSrSiO₄: Yb (Yb = 0 mol %, 1 mol %, 2 mol % and 3 mol %) nanophosphors were synthesized using the co-precipitation method, and their comparative structural and optical properties were studied to demonstrate the effect of Yb ion on the characteristic properties of the prepared nanophosphors. The powder X-ray diffraction (PXRD) patterns of BaSrSiO₄:Yb and CaSrSiO₄:Yb suggest the formation of a single-phase orthorhombic structure with space groups Pbnm and Pna21, respectively. The Raman shifts in BaSrSiO₄ (BSS) and CaSrSiO₄ (CSS) indicate out-of-phase bending of Sr–O and symmetric stretching of Si–O. The FTIR spectra show bands in the spectra between 1033 and 1063 cm⁻¹, which can be attributed to the vibration of the Si–O-Si bond in both samples. The result also supported the formation of orthosilicate. SEM revealed agglomerated chunks in the BSS samples and rod-like structures in the CSS samples. The PL spectra show a significant change in the intensity of the emission peak at 975 nm following the transition ²F_7/2 → ²F_5/2 for different alkali earth metals (Ca, Ba), which is related to the energy level and formation of Yb²⁺ ion in the respective hosts. In CaSrSiO₄ doped Yb a red emitting band at 700 nm is observed which is not present in BaSrSiO₄ host.