Stability of Luminescent Trivalent Cerium in Silica Host Glasses Modified by Boron and Phosphorus Carmen Canevali, ² Mariachiara Mattoni, ² Franca Morazzoni, ² Roberto Scotti,* ,² Mariano Casu, ‡ Anna Musinu, ‡ Radenka Krsmanovic, § Stefano Polizzi, § Adolfo Speghini, | and Marco Bettinelli | Contribution from the Dipartimento di Scienza dei Materiali, UniVersita ` di Milano-Bicocca, INSTM, Via Cozzi 53, 20125 Milano, Dipartimento di Scienze Chimiche, UniVersita ` di Cagliari, INSTM, SS554 BiVio per Sestu, 09042 Monserrato (CA), Dipartimento di Chimica Fisica, UniVersita ` Ca’ Foscari, INSTM, Via Torino 155/b, 30172 Venezia-Mestre, and Dipartimento di Scientifico e Tecnologico, UniVersita ` di Verona, INSTM, strada le Grazie 15, 37134 Verona, Italy Received April 18, 2005; E-mail: Roberto.Scotti@unimib.it Abstract: 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), 31 P, 29 Si, and 11 B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV-vis absorption investigations demonstrated that, in PSG and BPSG, Ce 3+ ions interact with phosphoryl, [OdPO3/2], metaphosphate, [OdPO2/ 2O] - , and pyrophosphate, [OdPO1/2O2] 2- , groups, linked to a silica network. This inhibits both CeO2 segregation and oxidation of isolated Ce 3+ ions to Ce 4+ , up to Ce:Si ) 5 × 10 -3 . In BSG, neither trigonal [BO3/2] nor tetrahedral [BO4/2] - boron units coordinate cerium; thus, Ce 3+ 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 Ce 3+ oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce 3+ emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth. Introduction Ce-doped crystalline compounds have received great interest owing to the rare-earth (RE) luminescence properties. 1,2 In fact, trivalent cerium has a broad emission band in the UV-vis region due to the allowed 5d-4f transition. As the energies of the 5d levels are strongly affected by the crystal field around Ce 3+ , significant shifts of the emission energy occur in different host crystalline matrixes. 3 Notable properties of luminescent Ce 3+ ions are the fast 5d-4f decay time and the relatively high light output, which make Ce 3+ -containing solids promising materials in several applications such as phosphors for cathodolumines- cence, 4 scintillators for applications in high-energy physics 5-7 and for the detection of X-rays, γ-rays, or neutrons, 8-12 and tunable solid-state lasers operating in the near-UV, violet, and blue regions. 13-18 The luminescence yield is unfavorably affected by Ce 3+ aggregation phenomena. 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