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Stability of Luminescent Trivalent Cerium in Silica Host Glasses Modified by Boron and Phosphorus

2005; American Chemical Society; Volume: 127; Issue: 42 Linguagem: Inglês

10.1021/ja052502o

1943-2984

Carmen Canevali, M. Mattoni, Franca Morazzoni, Roberto Scotti, Mariano Casu, A. Musinu, Radenka Krsmanović, Stefano Polizzi, Adolfo Speghini, Marco Bettinelli,

Lanthanide and Transition Metal Complexes

Ce-doped borosilicate (BSG), phosphosilicate (PSG), and borophosphosilicate (BPSG) glasses (B:P:Si molar ratios 8:0:92, 0:8:92, and 8:8:84; Ce:Si molar ratio 1 × 10-4 to 1 × 10-2) were prepared by the sol−gel method. High-resolution transmission electron microscopy (HRTEM), 31P, 29Si, and 11B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV−vis absorption investigations demonstrated that, in PSG and BPSG, Ce3+ ions interact with phosphoryl, [OPO3/2], metaphosphate, [OPO2/ 2O]-, and pyrophosphate, [OPO1/2O2]2-, groups, linked to a silica network. This inhibits both CeO2 segregation and oxidation of isolated Ce3+ ions to Ce4+, up to Ce:Si = 5 × 10-3. In BSG, neither trigonal [BO3/2] nor tetrahedral [BO4/2]- boron units coordinate cerium; thus, Ce3+ oxidation occurs even at Ce:Si = 1 × 10-4, as in pure silica glass (SG). The homogeneous rare-earth dispersion in the host matrix and the stabilization of the Ce3+ oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce3+ emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth.