Tuning the energetics and tailoring the optical properties of silver clusters confined in zeolites

The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal-host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the cluster's optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.status: publishe

Silver Zeolite Composites-Based LEDs: a Novel Solid-State Lighting Approach

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Silver clusters incorporated in a zeolite matrix represent a promising alternative for rare earth phosphors, organic dyes, and quantum dots as emitters in organic and hybrid organic/inorganic light-emitting diodes (OLEDs). Compared to other existing types of emitters, they combine an excellent stability to oxygen and humidity with a high luminescence quantum yield and color tunability. This study reports on the first use of these silver exchanged zeolites embedded in polyvinyl carbazole (PVK), which is expected to act as a conducting matrix, as emitters in a single-layer OLED. It is demonstrated that the introduction of these Ag zeolites leads to electroluminescence bands that clearly differ from pristine PVK OLEDs as well as from the photoluminescence spectra of the Ag zeolites. The current density and the spectral properties observed in these devices are strongly influenced by the zeolite silver loading, paving the way for a new type of easily tunable hybrid and cost-effective OLEDs.status: publishe

Enhanced Luminescence and Mechanistic Studies on Mn-doped Double Layered Perovskite Phosphors: Cs4Mn1−xCdxBi2Cl12

Halide perovskites offer great promise for optoelectronic applications, but stability issues continue to hinder its implementation and long-term stability. The stability of all-inorganic halide perovskites and the inherent quantum confinement of low dimensional perovskites can be harnessed to synthesize materials with high PL efficiency. An example of such materials is the recently reported new family of layered double perovskites, Cs4Mn1−xCdxBi2Cl12. Herein, we report a new synthetic procedure that enhances the maximum PLQY of this family materials to up 79.5%, a 20% enhancement from previous reports and the highest reported for a Mn-doped halide perovskite. Importantly, stability tests demonstrate that these materials are very stable towards humidity, UV irradiation, and temperature. Finally, we investigated the photophysics, the effects of magnetic coupling and temperature in the PL efficiency and proposed a mechanism for the emission process. Our results highlight the potential of this family of materials and related layered all-inorganic perovskites for solid-state lighting and optoelectronic applications</p

Biodiesel Production Using Lithium Metasilicate Synthesized from Non-Conventional Sources

A facile and versatile process to produce lithium metasilicate (Li2SiO3) from non-conventional silicon sources (two different sand sources from the central area of M&eacute;xico) was developed. The synthesis protocol based on a solid-state reaction followed by a hydrothermal treatment resulted in highly pure lithium metasilicate, as corroborated by XRD, SEM-EDS, and XPS analysis. Furthermore, lithium metasilicate was used as a heterogeneous catalyst for biodiesel production from soybean oil, where conversion yields were compared according to the silicon source used (based on chemical purity, stability, and yield efficiency). The best performing metasilicate material displayed a maximum of 95.5% of biodiesel conversion under the following conditions: 180 min, 60 &deg;C, 5% catalyst (wt./wt., catalyst-to-oil), and 18:1 (methanol:oil). This contribution opens up alternatives for the production of lithium metasilicate using non-conventional precursors and its use as an alternative catalyst in biodiesel production, displaying better chemical stability against humidity than conventional heterogeneous catalysts

Silver Zeolite Composite-Based LEDs: Origin of Electroluminescence and Charge Transport

In this contribution, we report on the first time use of silver-exchanged zeolites embedded in the nonconductive polystyrene (PS) and their use as hybrid emitters in light-emitting diodes (ZEOLEDs). The turn on voltage and EL intensity are strongly dependent on the concentration of metal clusters. It is shown that the key to optimize this technology is improving the zeolite anode contact. Such an optimized device based on cheap abundant materials could provide an alternative for the commercial phosphor converted LEDs. A ZEOLED with a voltage polarity dependent color is demonstrated.status: publishe