“…In addition, a new small emission peak at 621 nm (shown in Figure ) that corresponds to the 5 D 0 − 7 F 2 transition is also observed above 4 GPa. Therefore, it can be deduced that the new site symmetry of Eu 3+ ions is lower (such as in orthorhombic ( D 2 , C 2 v ), monoclinic ( C 2 , C S ), or triclinic ( C 1 ) structures) at pressures higher than 4 GPa. ,, To determine the new site symmetry of Eu 3+ ions at 4−8 GPa, the 5 D 0 → 7 F 0 transition of Eu(OH) 3 rods at different pressures has been checked and summarized in Figure . Although the intensity of this transition is very weak as compared with that of the 5 D 0 → 7 F 1,2 transitions at the same pressure, some information can still be obtained.…”