Confinement of Highly Luminescent Silver Nanoclusters in FAUY Zeolite: A Study on the Formation Effects of Silver Nanoclusters and the Sensitization of Tb³⁺

Abstract

In this research, highly luminescent silver nanoclusters (Ag NCs) were prepared by using Na-FAUY zeolite as a scaffold to hinder their aggregation, and efficient energy transfer from Ag NCs to Tb3+ was realized in Ag+-Tb3+ dual-exchanged Na-FAUY zeolites and then proved by steady spectral and luminescence lifetime measurements. Furthermore, the effects of Ag+ loading amount, thermal treatment, and Tb3+ loading on the luminescence properties of Ag NCs were studied, and the optimized doping and preparing conditions were obtained. X-ray photoelectron spectroscopy together with spectral measurements indicated that the available sites for Tb3+ and Ag+ are competitive and Tb3+ doping may hinder the effective formation of Ag NCs. It is also indicated that the loading of Tb3+ may lead to reduced Si/Al ratios, which greatly influence the luminescence property and chemical state of Ag NCs, e.g., a high Si/Al ratio leads to blueshift emission and stronger ionic of Ag NCs. This research may benefit the design of Ag NCs-involved luminescent zeolites that have potential applications for photonic devices like LEDs and 3D displays.

Luminescence Control of Silver Nanoclusters by Tailoring Extra-Framework Cations in FAU-Y Zeolite: Implications for Tunable Emission

“…Interestingly, the extra-framework cations also manipulate the emission peak of Ag NCs confined inside the FAU-Y zeolites; the PL spectra of Ag NCs exhibit a continuous red-shift peak wavelength from 512 nm in 2LiY20Ag to 520 nm in NaY20Ag and 528 nm in 2CaY20Ag. This is caused by the increased lattice parameter of the host zeolite (Figure b), as the expanded unit cell may reduce the local crystal field of Ag NCs, and thus, the energy separation between the ground state and the excited state of the Ag NCs is reduced . That this lattice parameter induced the red/blue-shift emission of Ag NCs is very clear when compared with the previously reported emission peak wavelength in LTA or FAU zeolites with different unit cells. , Accordingly, an increase in the full width at half-maximum (FWHM) of the PL spectra can be observed from 65 nm in 2LiY20Ag to 70 nm in NaY20Ag and 73 nm in 2CaY20Ag, indicating that the coupling between the luminescent center of the Ag NCs and the host lattice becomes stronger.…”

“…This is caused by the increased lattice parameter of the host zeolite (Figure b), as the expanded unit cell may reduce the local crystal field of Ag NCs, and thus, the energy separation between the ground state and the excited state of the Ag NCs is reduced . That this lattice parameter induced the red/blue-shift emission of Ag NCs is very clear when compared with the previously reported emission peak wavelength in LTA or FAU zeolites with different unit cells. , Accordingly, an increase in the full width at half-maximum (FWHM) of the PL spectra can be observed from 65 nm in 2LiY20Ag to 70 nm in NaY20Ag and 73 nm in 2CaY20Ag, indicating that the coupling between the luminescent center of the Ag NCs and the host lattice becomes stronger. Based on the PLE and PL spectra in Figure , the Stokes shift values of Ag NCs in 2LiY20Ag, NaY20Ag, and 2CaY20Ag are estimated to be 193, 212, and 220 nm, respectively; these monotonically increased Stokes shift values are also indicative of the enhanced excitation–phonon coupling. , …”

“…Taking the commercially available NaY ((Na 6.5 + )­[Al 6.5 Si 17.5 O 48 ]) as the parent zeolite in this work, the LiY and CaY zeolites were prepared using the ion-exchange method. According to our previous work and published reports, , 1 g of NaY zeolite each was suspended separately in 50 mL of LiNO 3 aqueous solution with concentrations of 2.0 and 5.0 mol/L, or in 50 mL of Ca­(NO 3 ) 2 ·4H 2 O aqueous solution with a concentration of 2.0 mol/L. The above suspensions were kept stirring for 24 h at 80 °C, and then recovered by filtration and washed with deionized water three times before drying at 80 °C for 24 h. Finally, the Li + /Ca 2+ -exchanged zeolites were calcined at 300 °C for 2 h in air to remove impurities.…”

“…Recent research has indicated that the zeolite framework topology and extra-framework cations, external energy activation, silver loading degree, and rare-earth (RE) ion codoping greatly influence the formation and luminescence property of Ag NCs, suggesting that the improvement and manipulation of Ag NCs’ radiative emission for diverse applications are possible through structure design and control synthesis. For example, Ag NCs exhibit brighter emission in Li + partially exchanged LTA zeolites than in the Na + -type counterpart; the emission intensity of Ag NCs can be greatly improved by thermal treatment in FAU zeolites, and the optimized treatment temperature is related to the Ag + loading amount. − Ag NCs formatted under a mild thermal activation may not be suitable for lighting applications, as they are not stable enough; however, they can be used for low-content formaldehyde detection . The LTA­(Li)-Ag composite was suggested for humidity sensor application due to its remarkable dynamic change in Ag NCs emission color depending on the hydration level. , Besides, because of their tunable emission in the whole visible range and high quantum yield, Ag NCs have also been employed as sensitizers for f–f transition rare-earth (RE) ions like Eu 3+ , Tb 3+ , and Dy 3+ to improve their excitation efficiency or realize white light and tunable emission. − Furthermore, the growth dynamics of Ag NCs and the effect of RE dopants like Tb 3+ on the formation efficiency and chemical state of Ag NCs have been studied using the modified Auger parameter and fluorescence microscopy. , …”

Tunable luminescence of silver-exchanged SOD zeolite thermally treated under mild conditions

“…39 The absorption band at 282 nm is ascribed to silver nanoclusters, 40 such as Ag 3 n+ , Ag 4 m+ (mainly observed at low and intermediate silver loading samples) and Ag 6 p+ (at higher silver contents) clusters. 23,41 The absorption band at 415 nm is attributable to large silver nanoparticles, 42,43 which can be seen in the transmission electron microscopy (TEM) image. The dark spots appear on the SOD zeolites and display a lattice spacing distance of 0.2475 nm (Fig.…”