The conversion of ultraviolet (UV) to near-infrared (NIR) photons is demonstrated for the first time in Yb 3+containing glass via Sn 2+ . Glasses with barium phosphate matrix were prepared by melt-quenching adding 2 mol % Yb 2 O 3 alongside SnO up to 10 mol %. The investigation encompassed X-ray diffraction (XRD), UV−vis-NIR absorption, 119 Sn Mossbauer spectroscopy, and photoluminescence (PL) spectroscopy measurements with emission dynamics assessment. XRD data showed that the amorphous nature of the glasses is maintained within the range of dopant concentrations considered, while the optical absorption, 119 Sn Mossbauer, and PL data supported the occurrence of divalent tin centers. The NIR PL data showed that exciting Sn 2+ centers around 290 nm results in the NIR emission from Yb 3+ near 1000 nm which becomes more intense with the increase in SnO. The Yb 3+ decay curves revealed a rise time for the 2 F 5/2 emitting level followed by a single exponential decay. An energy transfer process proceeding via charge transfer states involving tin (donor) and ytterbium (acceptor) was proposed to account for the enhanced UV-excited NIR emission from Yb 3+ ions.
The synthesis of derivatives of the Noria macrocycle
and the structurally
similar macrocycle, R3, each containing 12 sulfonic acid groups, is
reported. Herein, we demonstrate their utility as reusable Brønsted
acid catalysts for the Biginelli synthesis of dihydropyrimidinones
and the Pechmann synthesis of coumarins. We also demonstrate that
the supramolecular structure directs the reagents to interact with
the sulfonic acid catalytic sites, thus increasing the catalyst’s
efficiency compared to other monomeric, macrocyclic, and polymeric
sulfonic acid catalysts.
The products of thermal
decomposition of iron nitrate nonahydrate
doped into poly(vinylidene difluoride) are examined using Mössbauer
spectroscopy. Very little of the expected nitrogen dioxide product
is observed, which is attributed to Fe3+ catalysis of the
decomposition of NO2. The active site of the catalysis
is shown to be Fe(OH)3 in the polymer matrix, which is,
unexpectedly, reduced to Fe(OH)2. Thermodynamic calculations
show that the reduction of Fe3+ is exergonic at sufficiently
high temperatures. A reaction sequence, including a catalytic cycle
for decomposition of NO2, is proposed that accounts for
the observed reaction products. The role of the polymer matrix is
proposed to inhibit transport of gas-phase products, which allows
them to interact with Fe(OH)3 doped in the polymer.
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