Luminescent silver–lithium-zeolite phosphors for near-ultraviolet LED applications

Abstract

Silver clusters (AgCLs) confined in zeolites show remarkable luminescence properties, displaying high photoluminescence quantum efficiencies combined with tunable visible light emission characteristics, making them highly promising phosphors in lighting devices. However, to date the lack of efficient near-ultraviolet (NUV) and blue excitable silver zeolites has hindered their use in remote LEDs. In this report, we show the utilization of Ag-zeolites in a NUV-LED device, displaying highly efficient green emission with an external quantum efficiency of 83% and a broad excitation range between 300 and 400 nm. This phosphor material was obtained by confining AgCLs in a dehydrated fully Li-exchanged Linde-type A (LTA) zeolite. The unique effect of Li⁺ ions and dehydration, on the luminescence properties of AgCLs, originates from the structural changes of both the zeolite framework, and the ligand coordinated tetrahedral Ag₄ clusters, as observed by X-ray diffraction analysis and X-ray excited optical luminescence–X-ray absorption fine structure (XEOL-XAFS) method, respectively. Moreover, photophysical evidence showed long decay times for these samples in the order of 210 μs, responsible for the steady-state emission, which most likely originates from the decay of the triplet state with a charge transfer character of Ag₄(O₂) tetrahedral clusters surrounded by 6 lithium cations confined in the sodalite cages of LTA zeolites.