Zeolite-Encaged Luminescent Silver Nanoclusters.

Silver nanoclusters (Ag NCs) are nanoscale aggregates that possess molecular-like discrete energy levels, resulting in electronic configuration-dependent tunable luminescence spanning the entire visible range. Benefiting from the efficient ion exchange capacity, nanometer dimensional cages, and high thermal and chemical stabilities, zeolites have been employed as desirable inorganic matrices to disperse and stabilize Ag NCs. This paper reviewed the recent research progresses on the luminescence properties, spectral manipulation, as well as the theoretical modelling of electronic structure and optical transition of Ag NCs confined inside various zeolites with different topology structures. Furthermore, potential applications of the zeolite-encaged luminescent Ag NCs in lighting, gas monitoring and sensing were presented. This review concludes with a brief comment on the possible future directions in the study of zeolite-encaged luminescent Ag NCs.

Tailoring the Luminescence Properties of Silver Clusters Confined in Faujasite Zeolite through Framework Modification.

Faujasite zeolites with a regular micropore and mesopore structure have been considered desirable scaffolds to stabilize luminescent silver nanoclusters (Ag CLs), while turning of the emission properties of the confined Ag CLs is still under investigation. In this study, the desilicated and dealuminated faujasite zeolites were first prepared to modify the zeolite framework and Si/Al ratio before Ag+ loading. With thermal treatment on the thereafter Ag+-exchanged zeolites, the Ag CLs formatted inside the D6r cages showed red-shifted emission in the desilicated zeolites and blue-shifted emission in the dealuminated zeolites, so that a tunable emission in the wavelength range of 482-528 nm could be obtained. Meanwhile, the full width at half maximum of the emission spectra is also closely related with framework modification, which monotonously increases with enhancing Si/Al ratio of host zeolite. The XRD, XPS, and spectral measurements indicated that the tunable luminescence properties of Ag CLs result from the controlling of local crystal field and coupling between host lattice and luminescent center. This paper proposes an effective strategy to manipulate the emission properties of Ag CLs confined inside zeolites and may benefit the applications of noble metal clusters activated phosphors in imaging and tunable emission.

Thermal-Driven Formation of Silver Clusters Inside Na/Li FAUY Zeolites for Formaldehyde Detection.

In this research, the LiY zeolite was firstly synthesized by using NaY as the parent zeolite; thereafter, the LiYAg and NaYAg zeolites created for formaldehyde gas detection were prepared with further Ag+-Li+/Na+ exchange and a mild thermal treatment at 300 °C to promote the formation of luminescent Ag CLs. The spectra experimental results indicated that Ag CLs showed stronger and blue-shifted emissions in LiYAg compared with in NaYAg, and the emission intensity of Ag CLs in both zeolites monotonously decreased when exposed to increasing formaldehyde gas content. Moreover, the linear dependence of the Ag CLs' emission intensity variation on formaldehyde content indicated a reliable method for fast and sensitive formaldehyde detection. According to the XPS, UV-vis absorption, and N2 adsorption-desorption isotherm studies, the formaldehyde-gas-induced luminescence quenching of Ag CLs is due to the formation of Ag2O and Ag NPs, in which the higher content of Ag+/Ag0 redox couples in LiYAg and larger surface area of NaYAg benefit the precise detection of formaldehyde gas in low- and high-content ranges, respectively. Furthermore, the blue-shifted peak position and widened FWHM of Ag CLs can also be used for the indication of formaldehyde gas and the detection limit of NaYAg and LiYAg, which both meet with the standards of the WHO and OSHA.