Synthesis, Structure, and Thermally Stable Luminescence of Eu²⁺-Doped Ba₂Ln(BO₃)₂Cl (Ln = Y, Gd and Lu) Host Compounds

A new family of chloroborate compounds, which was investigated from the viewpoint of rare earth ion activated phosphor materials, have been synthesized by a conventional high temperature solid-state reaction. The crystal structure and thermally stable luminescence of chloroborate phosphors Ba₂Ln(BO₃)₂Cl:Eu²⁺ (Ln = Y, Gd, and Lu) have been reported in this paper. X-ray diffraction studies verify the successful isomorphic substitution for Ln³⁺ sites in Ba₂Ln(BO₃)₂Cl by other smaller trivalent rare earth ions, such as Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. The detailed structure information for Ba₂Ln(BO₃)₂Cl (Ln = Y, Gd, and Lu) by Rietveld analysis reveals that they all crystallize in a monoclinic P2₁/m space group. These compounds display interesting and tunable photoluminescence (PL) properties after Eu²⁺-doping. Ba₂Ln(BO₃)₂Cl:Eu²⁺ phosphors exhibit bluish-green/greenish-yellow light with peak wavelengths at 526, 548, and 511 nm under 365 UV light excitation for Ba₂Y(BO₃)₂Cl:Eu²⁺, Ba₂Gd(BO₃)₂Cl:Eu²⁺, and Ba₂Lu(BO₃)₂Cl:Eu²⁺, respectively. Furthermore, they possess a high thermal quenching temperature. With the increase of temperature, the emission bands show blue shifts with broadening bandwidths and slightly decreasing emission intensities. It is expected that this series of chloroborate phosphors can be used in white-light UV-LEDs as a good wavelength-conversion phosphor.