Host-Guest Engineering of MOF-808 for Random Lasing and Solid-State Emission

Abstract

Fluorescent organic dyes have a broad range of applications across various fields. However, their use is threatened by stability issues such as photobleaching and aggregation-caused quenching that prevent them from showing solid-state luminescence and being used in high-power photonics applications for a long period. One possibility to overcome these problems is to embed dye molecules within a hosting platform. Metal-organic frameworks (MOFs) are among the best candidates to overcome these problems due to their porous nature, which provides excellent sorption capacities while ensuring stability for potential guest molecules, even in extreme environments. In this work, we investigate the optical performance of rhodamine B and coumarin 343 when interacting with Zr-based MOF-808. On one hand, we demonstrate that inclusion of dye molecules in MOF-808 cavities prevents aggregation-induced quenching, enabling the use of dyes in powdered form and enhancing their emission in solid-state applications, such as fingerprint detection. On the other hand, the dye-MOF interaction in solution reveals that MOF-808 nanoparticles act as efficient scatterers, significantly enhancing random lasing emission by narrowing the emission spectra and reducing the lasing threshold. The lasing performance is shown to be dependent on the MOF concentration and excitation intensity, with an optimal concentration minimizing the threshold and bandwidth. Finally, we demonstrate the feasibility of combining MOF-808 nanoparticles and dyes into polymeric thin films, where the MOFs contribute to halving the lasing threshold, making the system suitable for portable lasing applications.

Keywords: host−guest nanosystems; metal–organic frameworks; nanocomposites; portable lasing device; random lasing.

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(a) Precursors used in the synthesis of MOF-808. (b) Scheme of the solid-state emitting system with RhB encapsulated within the pores of the MOF (RhB–MOF-808). (c) Scheme of the liquid-phase system in which MOF nanoparticles are used as passive scatterers (RhB in H₂O + MOF). (d) Scheme of the thin-film system in which MOF nanoparticles are used as passive scatterers (PVA RhB film + MOF). (e) Fluorescence emission of bare RhB in water pumped at 2.2 mJ (magenta filled curve) compared with the emission of bare RhB at 0.5 mJ (black dotted curve) and lasing emission of a solution of RhB in water with the addition of MOF nanoparticles as scatterers (relative picture in the inset). (f) Photoluminescence of powdered RhB embedded in MOF-808 (blue filled curve) and lasing arising from the same powder (orange filled curve). (g-i) Bare RhB under UV light. (g-ii) RhB–MOF-808 under UV light. (g-iii) Bare RhB under daylight (g-iv) RhB–MOF-808 exposed to daylight. (h) Impression of a fingerprint on (h-i) bare Cou dye and (h-iii) Cou–MOF-808 powder. (h-ii) FFT transform of a portion of the fingerprint impressed on bare Cou. (h-iv) FFT transform of the same portion of the fingerprint as that obtained with Cou–MOF-808 powder.

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(a–e) Threshold plots of solutions of RhB to which was progressively added an increasing concentration of scatterers starting from 0 mg/mL (bare RhB, panel a), Low (1.0 mg/mL, panel b), Medium (1.5 mg/mL, panel c), High (5.0 mg/mL, panel d), and Extra High (10.0 mg/mL, panel e). (f) Normalized spectra of bare RhB as a function of power. (g) Normalized spectra of RhB with the addition of MOFs (1.0 mg/mL) as a function of power. (h) Normalized spectra of Cou as a function of power. (i) Normalized spectra of Cou with the addition of MOFs (1.5 mg/mL) as a function of power. (l–p) Threshold plots of solutions of Cou in EtOH, in the presence of MOF nanoparticles with the same progression of increasing concentrations used for RhB in panels a–e.

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Contour plot of emission spectra collected as a function of delay time from excitation laser pulse in (a) aqueous solution of RhB; (b) RhB with MOF nanoparticles, 1.5 mg/mL; (c) Cou dissolved in EtOH; and (d) Cou solution where MOF nanoparticles were added (1.5 mg/mL). The intensity values are referred to the scale bar on the right. Kinetic decays derived from (a) and (b), (c) and (d), respectively, are shown in the inset and compared.

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(a) Normalized lasing spectra of RhB in aqueous solution with the addition of MOF scatterers at Low concentration (1.0 mg/mL, filled green curve), polymeric film prepared starting from a solution of bare RhB (red dotted curve), while the continuous black curve represents the spectrum of the film obtained with the addition of MOF nanoparticles as scatterers (shown in the inset as a picture). (b) Threshold plot of the polymeric film containing MOF nanoparticles (10 mg/mL), in which red dots represent the intensity as a function of increasing power, while blue squares represent the FWHM. Dashed lines are a guide to the eye.