Electronic Spectra and Crystal-Field Analysis of Europium in Hexanitritolanthanate Systems

The luminescence spectra of Eu(3+) at a T(h) point-group site in the hexanitritolanthanate systems Cs(2)NaEu((14)NO(2))(6), Cs(2)NaEu((15)NO(2))(6), Rb(2)NaEu((14)NO(2))(6), Cs(2)LiEu((14)NO(2))(6), and Cs(2)NaY((14)NO(2))(6):Eu(3+) have been recorded between 19,500 and 10,500 cm(-1) at temperatures down to 3 K. The spectra comprise magnetic-dipole-allowed zero phonon lines, odd-parity metal-ligand vibrations, internal anion vibrations, and lattice modes, with some weak vibrational progressions based upon vibronic origins. With the aid of density functional theory calculations, the vibrational modes in the vibronic sidebands of transitions have been assigned. The two-center transitions involving NO(2)(-) stretching and scissoring modes are most prominent for the (5)D(0) → (7)F(2) hypersensitive transition. The onset of NO(2)(-) triplet absorption above 20,000 cm(-1) restricts the derived Eu(3+) energy-level data set to the (7)F(J) (J = 0-6) and (5)D(0,1) multiplets. A total of 21 levels have been included in crystal-field energy-level calculations of Eu(3+) in Cs(2)NaEu(NO(2))(6), using seven adjustable parameters, resulting in a mean deviation of ~20 cm(-1). The comparison of our results is made with Eu(3+) in the double nitrate salt. In both cases, the fourth-rank crystal field is comparatively weaker than that in europium hexahaloelpasolites.