Silver-zeolite clusters could replace expensive, toxic phosphors

Space confinement of clusters of metallic atoms is a versatile method to control and enhance the electrical and optical properties of nanomaterials. Researchers at the University of Leuven (KU Leuven; Leuven, Belgium) and the University of Strasbourg (Strasbourg, France) have successfully used zeolites—natural, porous minerals that can also be synthetically produced—to incorporate silver nanoclusters in a well-defined framework with molecular-scale channels and cavities. Through customization of the zeolite host, the properties of the silver clusters can be tuned to create photoluminescent materials that emit from deep red to green with luminescence efficiencies of nearly 100%.

Starting from a variety of classes of zeolite materials with different silicon-to-aluminum ratios and containing different alkali metal ions, silver uptake was accomplished through cation exchange by immersing zeolite materials in a silver nitrate bath. After thermal treatment at 450°C, the silver-zeolites became luminescent. Characterization of these materials using x-ray photoelectron spectrometry (XPS) and extended x-ray absorption fin structure (EXAFS) revealed that the zeolite geometry and the charge density of the alkali environment affected the configuration of embedded silver nanoclusters, and allowed a greater-than 0.5 eV tuning of their ionization potential. Illumination of various nanoclusters by monochromatic light from a fluorimeter resulted in highly efficient photoluminescence from red to green (500–700 nm, with full-width half-maximum at approximately 100 nm) with external quantum efficiencies between 50% and 97%. Zeolites, commonly used in washing powders, combined with silver particles could be a far more economical option than expensive and sometimes-toxic phosphors. Reference: O. Fenwick et al., Nat. Mater.; doi:10.1038/nmat4652 (Jun. 6, 2016).