Theoretical and experimental investigation of Gd³⁺-doped white light-emitting chlorapatite Ca_6-xNa₂Y₂(SiO₄)6Cl₂ synthesized by hydrothermal route

A series of white light-emitting Ca_6-xNa₂Y₂(SiO₄)6Cl₂:Gd³⁺ chlorapatite compounds were synthesized by liquid solid solution-based hydrothermal method. The structural, electronic and optical properties of synthesized chlorapatite were studied in detail. The X-ray diffraction (XRD) analysis confirms the formation of monoclinic structure with space group P21/c. Fourier transform infrared spectroscopy shows different modes of SiO₄ tetrahedron, with no impurity peaks due to (OH) and (CO₂) group. Theoretical calculations were done by B3LYP hybrid GGA approximation using density functional theory. The computational band gap value of 3.8 eV was calculated using 3 x 3 x 3 Monkhorst mesh, which satisfies the experimental value of 4.3 eV calculated by diffuse transmittance spectroscopy. The band gap value calculated by molecular orbital theory was found to be 4.01 eV, which satisfied the above results. Mulliken population analysis shows that Y bonds are more covalent in nature as compared to Ca and Na bonds. The photoluminescence emission peaks obtained at 468 nm, 482 nm, 492 nm, 549 nm and 661 nm are perceived due to ⁶G_7/2 – ⁶D_J, ⁶G_7/2 – ⁶I_J and ⁶P_J – ⁸S_7/2 transitions in white region under 220 nm UV excitation. (author)