INFLUENCE OF HYDROSTATIC-PRESSURE AND OF INTERATOMIC DISTANCE UPON THE ENERGY-LEVELS SCHEME OF EU3+ IN REOBR (RE=LA, GD OR Y)

The free ion energy level positions and the crystal held in Eu3+ are studied under high pressure and along a host series LaOBr-GdOBr-YOBr. The results show that the CF parameters fitted by F-7(J) together D-5(J) energy levels are different from those fitted by only F-7(J) levels. The CF strength, the Slater parameters F-k and the spin-orbit coupling parameter zeta for Eu3+ decrease with increasing pressure and with decreasing interatomic distance along the host series LaOBr-GdOBr-YOBr. The best-fit value of F-2, F-4 and zeta of Eu3+ in LaOBr decreases by 1.58%, 0.69% and 1.36%, respectively, from OGPa to 13 GPa. A combined covalency-expanding mechanism is proposed for understanding the reduction in free-ion parameters with increasing pressure and with decreasing interatomic distance.