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

Abstract

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.

Stable and Highly Luminescent Silver Nanoclusters in the 13X Zeolite Enabled by Mg2+ Doping and Their Luminescence Tuning by Heating Temperature

“…23 On the other hand, the characteristic peak at 6°shifts toward the larger angle by increasing Mg 2+ content in the 13X zeolite, as shown in Figure 1F, implying the lattice contraction of 13X owing to the replacement of the larger Na + by the smaller Mg 2+ (ionic radius: Na + = 1.02 Å, Mg 2+ = 0.66 Å). 9,14,24 The structure alteration caused by Mg 2+ can be further verified by Raman spectra, as shown in Figure 3B,C. The vibration bands centered at around 290 and 380 cm −1 are assigned to the D6s in the 13X zeolite, showing a visible shift toward a lower wavenumber with increasing Mg 2+ content compared to the parent 13X zeolite.…”

“…On the one hand, the uneven charge distributions caused by Mg 2+ doping can provide an internal electric field inside 13X by spontaneous polarization, which can propel the migration of electrons and accelerate reaction kinetics and further promote the self-assembly of more luminescent silver nanoclusters formed by Ag + and Ag 0 . , The XRD pattern shown in Figure A shows slight difference for the relative intensities of some diffraction peaks between Ag-13X and 0.1Mg-Ag-13X, owing to the redistribution of charge balancing cations caused by the introduction of Mg 2+ . On the other hand, the characteristic peak at 6° shifts toward the larger angle by increasing Mg 2+ content in the 13X zeolite, as shown in Figure F, implying the lattice contraction of 13X owing to the replacement of the larger Na + by the smaller Mg 2+ (ionic radius: Na + = 1.02 Å, Mg 2+ = 0.66 Å). ,, The structure alteration caused by Mg 2+ can be further verified by Raman spectra, as shown in Figure B,C. The vibration bands centered at around 290 and 380 cm –1 are assigned to the D6s in the 13X zeolite, showing a visible shift toward a lower wavenumber with increasing Mg 2+ content compared to the parent 13X zeolite.…”

“…On the contrary, an opposite effect is observed in the sample Ag-13X, whereby the D6r band undergoes a slight red shift and a broadening of its width. This spectral change is owing to the fact that D6s are occupied by larger Ag + compared with Na + (ionic radius: Ag + = 1.26 Å), which leads to longer bond distances and higher Si–O–Al angles in these composites, allowing a larger lattice spacing of 13X. ,, Besides, the higher charge density of divalent Mg 2+ compared with monovalent Na + induced the strong electrostatic interaction between the cations and the 13X framework, also leading to the shrinkage of the 13X framework and a smaller unit cell, which thereby results in more contracted [Ag 4 ] and better excellent optical performance of 0.1Mg-Ag-13X, similarly to the role enacted by Li + in Ag-LTA reported in previous studies. ,, However, Mg 2+ is much more effective in promoting the luminescence of the Ag-zeolite than Li + , as verified by the much higher PLQY (94.6%) of 0.1Mg-Ag-13X compared with that (83%) of Li + -exchanged Ag-LTA . This highlights that the size and valence state of extra-framework cations significantly influence the zeolite rigid framework and hereby affect the luminescent properties of the Ag-zeolite zeolite. ,,, …”

“…Silver nanoclusters confined within the zeolite are environmentally friendly, low-cost, and highly luminescent materials because of their simple synthesis procedure using cheap starting materials (zeolites), high stability, and attractive optical properties including high efficiency, large Stoke’s shift, tunable absorption, and emission, which make them highly useful in optoelectronic devices, luminescence sensing, date coding, etc. , Zeolites play critical roles in tuning the emission colors, the light absorption, and the luminescence efficiency of the formed silver nanoclusters within zeolites by varying several parameters such as the zeolite framework topology, chemical composition, choice of counterbalancing ions, and silver loading. − This is because such parameters can effectively affect the microenvironment where the silver nanoclusters are located and thereby all work to influence the geometry, dimension, and nuclearity. , By modulating one or several of the parameters, a series of luminescent materials derived from the confinement of silver nanoclusters within various zeolites, including LTA, FAU, SOD, and ANA, were reported, their emission color spans the whole visible spectral region and white emission is achieved, and the PLQY can be up to one unit in the FAUY zeolite. − Among the various parameters, the counterbalancing ions are highly attractive for tuning the optical features of silver nanoclusters confined within the zeolite since they can be very easily changed by the simple ion exchange procedure, and the effects they have on the luminescent properties are very prominent. For instance, Steele et al observed that the hypsochromic shift of the confined silver nanoclusters was realized by the gradual incorporation of Li + into the LTA zeolite .…”

“…3−8 This is because such parameters can effectively affect the microenvironment where the silver nanoclusters are located and thereby all work to influence the geometry, dimension, and nuclearity. 9,10 By modulating one or several of the parameters, a series of luminescent materials derived from the confinement of silver nanoclusters within various zeolites, including LTA, FAU, SOD, and ANA, were reported, their emission color spans the whole visible spectral region and white emission is achieved, and the PLQY can be up to one unit in the FAUY zeolite. 11−13 Among the various parameters, the counterbalancing ions are highly attractive for tuning the optical features of silver nanoclusters confined within the zeolite since they can be very easily changed by the simple ion exchange procedure, and the effects they have on the luminescent properties are very prominent.…”