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

Abstract: The crystal structure of β-Ca3SiO4Cl2 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 Eu2+-doped β-Ca3SiO4Cl2 phosphor were characterized. β-Ca3SiO4Cl2 was found to be monoclinic (space group P21/c) with the lattice parameters, a = 5.91234(1)？, b = 10.20128(1)？, c = 10.98866(1)？, β = 90.3423(1)˚. This structure can be considered as an intergrowth structure built up from alternating stacks of two layered sublattices, ■(2@∞)[Ca2SiO4] and ■(2@∞)[CaCl2], along [100] direction. In this structure, the Ca atoms occupy three crystallographically distinct sites; Ca1O4Cl3, Ca2O5Cl2, and Ca3O3Cl4. The photoluminescence of the Eu2+-doped Ca3SiO4Cl2 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. Effect 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.