Eu 3 + as a probe for rare-earth dopant site structure in nano-glass-ceramics

Abstract

Eu 3 + -doped transparent nano-glass-ceramics, 32(SiO2)9(AlO1.5)31.5(CdF2)18.5(PbF2)5.5(ZnF2):3.5(EuF3)mol %, have been prepared aiming at the investigation of the site structure of the Eu3+ rare-earth dopant. In this nano-glass-ceramic host, other rare-earth dopants, such as Er3+, Tm3+, Ho3+, and Dy3+, also have served as a dopant; however the Eu3+ ion is a preferably sensitive probe for a rare-earth dopant site structure due to its unique purely magnetic and purely electric dipole moment optical transitions involving the nondegenerate excited D50 and ground F70 states. The splitting in the respective emission and absorption spectra in the crystalline field of the nano-glass-ceramics and its parent glass has been studied. It has been concluded that the major site of the rare-earth dopant in the nano-glass-ceramics is nearly cubic, with an orthorhombic distortion according to the sequence Oh→D4h→D2h, and the majority of the rare-earth dopants substitute onto the Pb2+ site in the PbF2 nanocrystals embedded in the glass network. A vibronic contribution to the strength of the D50→F72 electric dipole moment transition has been found and the respective dominating contributing vibration mode has been proposed to be and to change as a2u→b1u→au, according to lowering the site symmetry in a sequence Oh→D4h→D2h.