The active lone pair electron effect and highly flexible coordination geometry of Pb2+ prevented the rational construction of metal–organic frameworks (MOFs) but promoted excellent fluorescence tuning. The regulation on organic and alkali templates facilitated the assemblies of three new Pb-MOFs: [Pb2(pia)2(DMA)]·DMA (1), [Pb2(pia)2(DMF)]·1.5DMF (2), and [Pb2(pia)2(DMF)]·NEt3 (3). They were rigid rod-spacer and double-walls frameworks, which possess defective dicubane [Pb4O6] based metal-carboxyl chains constructed from both semidirected and holodirected Pb2+ ions. These MOFs exhibited thermal stability up to 370 °C and unprecedented chemical stability in H2O and acidic (pH 2) and alkaline (pH 12) aqueous solutions, found for the first time in Pb-MOFs. A single-phase and rare-earth-free white-emitting phosphor, 1, was screen out, which showed a near-sunlight and human-vision-friendly broadband spectrum covering the full visible region, possessing the close-to-pure-white chromaticity coordinates of (0.332, 0.347), a near-daylight color temperature of 5696 K, and a high color rendering index of 95. The replacement of DMF as apical ligand and guest in 2 resulted in an intrinsic single and narrow emission at 562 nm with yellow color. The convenient yellow-and-blue color-tuning until white for 2 was realized by either solution or solid blending with blue-emissive H2pia, benefited from their highly matched excitation spectra. Using large NEt3 as template guest induced great framework distortion for 3 and led to white emission with chromaticity coordinates of (0.302, 0.294), stemming from nonequivalent dual emission at 450 and 545 nm. In-depth structure analysis revealed intra-/interchain Pb···Pb interactions in the lead(II)-carboxyl chains greatly affected the photochemical output.
Perovskite quantum dots (PQDs) have attracted extensive attention for various applications due to their hallmark optoelectronic properties. However, PQD gain materials are usually needed to be integrated with an external cavity to acquire effective optical feedback for lasing oscillation, which generally suffers from stringent fabrication procedures and the destruction of their pristine gain performance. In this work, we propose an approach to realize a new class of random lasers that are constructed by in situ precipitating perovskite quantum dots (PQDs) in metal–organic frameworks (MOFs). Such random lasers make full use of the combined merits of MOFs showing a high refractive index and a broad transmission window and that of PQDs exhibiting high optical gain. A lead-based MOF is utilized as a matrix, which allows us to grow PQDs at the Pb2+ sites in situ and thus produce high-density PQDs gain in MOFs. We experimentally demonstrate low-threshold multicolor random lasers achieved in the visible spectral range with different wavelengths through compositional modulation in the nanoporous environment of MOF nanostructures and illustrate potential applications of the developed PQDs@MOFs random laser as the illumination source in the speckle-free optical imaging. This study will pave the way for the construction of perovskite-based lasing in multifunctional systems.
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