Interplay between Crystal Structure and Photoluminescence Properties of β-Ca₃SiO₄Cl₂:Eu²⁺

The crystal structure of β-Ca 3 SiO 4 Cl 2 was determined by the ab initio structure determination method based on the synchrotron powder XRD data for the first time, and the luminescence properties of a Eu 2+ -doped β-Ca 3 SiO 4 Cl 2 phosphor were characterized. β-Ca 3 SiO 4 Cl 2 was found to be monoclinic (space group P 2 1 / c ) with the lattice parameters, a = 5.91234(1) Å, b = 10.20128(1) Å, c = 10.98866(1) Å, β = 90.3423(1)°. This structure can be considered as an intergrowth structure built up from alternating stacks of two layered sublattices, ∞ 2 [Ca 2 SiO 4 ] and ∞ 2 [CaCl 2 ], along the [100] direction. In this structure, the Ca atoms occupy three crystallographically distinct sites: Ca1O 4 Cl 3, Ca2O 5 Cl 2, and Ca3O 3 Cl 4 . The photoluminescence of the Eu 2+ -doped Ca 3 SiO 4 Cl 2 phosphor excited at 450 nm blue light shows the 150 nm wide-band emission peaked at 635 nm with about 70% quantum efficiency. The photoluminescence properties, such as centroid shifts, crystal-field splitting, and Stokes shifts, were correlated with the crystal structure through the calculation of shared-electron populations reflecting the bond covalency between Ca and O/Cl. Effects of doping concentrations on the luminescence spectra and temperature stability were also discussed based on the inhomogeneous energy transfer property determined by the structural geometric factor.