High-pressure synthesis via glass and photoluminescence properties of BaGe2O5 III-type SrSi2O5:Eu2+ with 12-coordinated Sr2+ site

BaGe 2 O 5 III-type SrSi 2 O 5 :Eu 2+ in which the Sr 2+ site is 12-coordinated, the highest coordination number among strontium silicates, has been successfully synthesized under high pressure and temperature, 16 GPa and 900 °C for 60 min using an almost glassy starting sample. It is found that the glassy state of the starting sample is much more useful to form SrSi 2 O 5 :Eu 2+ under high temperature and pressure compared to conventional solid-state reaction using a crystalline multiphase starting sample. Photoluminescence and cathodoluminescence of the SrSi 2 O 5 :Eu 2+ major-phase sample have been investigated in the ambient temperature and pressure conditions. SrSi 2 O 5 :Eu 2+ exhibits an emission peak at 379 nm which is shorter than those of the reported Eu 2+ -activated strontium silicate phosphors such as Sr 3 SiO 5 :Eu 2+ , Sr 2 SiO 4 :Eu 2+ , and SrSiO 3 :Eu 2+ . This is attributable to the cuboctahedral coordination of SrO 12 , i.e., EuO 12 in the BaGe 2 O 5 III-type SrSi 2 O 5 :Eu 2+ , which is more isotropic due to the higher coordination number of the Eu 2+ -site than those of other phosphors and results in reducing the crystal field splitting of the 5d level of Eu 2+ .