Buried truth: High‐field magic angle spinning dynamic nuclear polarization (MAS DNP) enhances the sensitivity of solid‐state NMR spectroscopy, but only for protonated surfaces. Direct 29Si DNP using the biradical TOTAPOL (see picture) circumvents this limitation by producing a 30‐fold enhancement of subsurface 29Si NMR signals in mesoporous silica, a material with applications in photonics, nanotechnology and catalysis.

We report on the sol-gel fabrication and characterization of (100−x)SiO2–xSnO2 (x=8, 16, and 25mol%) glass-ceramic waveguides doped with 1mol% Eu3+. A suitable top-down thermal process led to the formation of SnO2 nanocrystals ∼4nm embedding Eu3+ ions. The excitation spectra evidence the role of interband electronic transition of SnO2 nanocrystals on the luminescence of Eu3+. Monitoring the D05→F27 Eu3+ emission, we observe about 15 times increase in the intensity of SnO2 absorption band, moving from x=8to25mol%. These waveguides also exhibit low losses, making them quite promising for development of high-gain integrated optical amplifiers.

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