Optical spectroscopy of Pr3+ in the weberite, NaGdSb2O7: High covalence of Pr3+O2− bonding

Abstract The spectroscopic properties of the Pr 3+ ion in NaGdSb 2 O 7 are discussed in this paper. The host crystallizes in the orthorhombic weberite crystal structure with the general formula, A 2 B 2 O 7 . The Pr 3+ luminescence is dominated by emission transitions emanating from the 1 D 2 state. Transient fluorescent decay of the Pr 3+ luminescence is indicative of random distribution of Na + and Gd 3+ ions in NaGdSb 2 O 7 . The remarkable feature in the spectroscopic properties of the Pr 3+ ion is the very low energy of the interconfiguration Pr 3+ 4f 2 →4f 1 5d 1 excitation transition (3.63 eV; 342 nm). The large red shift of the Pr 3+ 4f 1 5d 1 configuration is connected with significant covalent contribution to the crystal field and the high covalence of the Pr 3+ O 2− bonding is tentatively assigned to chemical covalent bonding within the A 3 B tetrahedral moieties which surround the O 8h 2 − anion in the weberite structure. A comparative study of the optical properties of Pr 3+ in NaGdSb 2 O 7 and La 2 Hf 2 O 7 , which crystallizes with the pyrochlore structure, is also presented.