Noncentrosymmetric Lanthanide-Based MOF Materials Exhibiting Strong SHG Activity and NIR Luminescence of Er³⁺: Application in Nonlinear Optical Thermometry

Abstract

Optically active luminescent materials based on lanthanide ions attract significant attention due to their unique spectroscopic properties, nonlinear optical activity, and the possibility of application as contactless sensors. Lanthanide metal-organic frameworks (Ln-MOFs) that exhibit strong second-harmonic generation (SHG) and are optically active in the NIR region are unexpectedly underrepresented. Moreover, such Ln-MOFs require ligands that are chiral and/or need multistep synthetic procedures. Here, we show that the NIR pulsed laser irradiation of the noncentrosymmetric, isostructural Ln-MOF materials (MOF-Er3+ (1) and codoped MOF-Yb3+/Er3+ (2)) that are constructed from simple, achiral organic substrates in a one-step procedure results in strong and tunable SHG activity. The SHG signals could be easily collected, exciting the materials in a broad NIR spectral range, from ≈800 to 1500 nm, resulting in the intense color of emission, observed in the entire visible spectral region. Moreover, upon excitation in the range of ≈900 to 1025 nm, the materials also exhibit the NIR luminescence of Er3+ ions, centered at ≈1550 nm. The use of a 975 nm pulse excitation allows simultaneous observations of the conventional NIR emission of Er3+ and the SHG signal, altogether tuned by the composition of the Ln-MOF materials. Taking the benefits of different thermal responses of the mentioned effects, we have developed a nonlinear optical thermometer based on lanthanide-MOF materials. In this system, the SHG signal decreases with temperature, whereas the NIR emission band of Er3+ slightly broadens, allowing ratiometric (Er3+ NIR 1550 nm/SHG 488 nm) temperature monitoring. Our study provides a groundwork for the rational design of readily available and self-monitoring NLO-active Ln-MOFs with the desired optical and electronic properties.

Multimodal Optically Nonlinear Nanoparticles Exhibiting Simultaneous Higher Harmonics Generation and Upconversion Luminescence for Anticounterfeiting and 8‐bit Optical Coding

“…This is because polycrystalline, micro-and nanosized materials are composed of a large number of small crystallites with random orientations, which allows for the detection of averaged NLO signal such as SHG. [1,18,25,56] Hence, precise phase-matching for each crystal is no longer required. Therefore, we chose polycrystalline LiNbO 3 nanoparticles (NPs) as the phase for designing our NLO material platform (Figure 1a).…”

“…To quantitatively evaluate the SHG performance of our NPs, we compare the signal intensity to that of KDP powders, commonly employed as reference (Figure 3d; Figure S11, Supporting Information). [14,17,18,60] The SHG signal from the LiNbO 3 NPs is significantly higher (up to 80-fold) compared to the reference KDP powders, and it is hardly influenced by the Ln doping (Figure S11, Supporting Information). A similar excitationwavelength dependence of the SHG intensities is observed for our LiNbO 3 NPs and KDP powders (Figure 3d; Figure S12, Supporting Information).…”

“…Nonetheless, SHG phenomena can be also observed in polycrystalline materials, such as organic compounds, [14,15] metal-organic frameworks (MOFs), [16][17][18] plasmonic nanomaterials, [19][20][21] metasurfaces, [22,23] semiconductors, [24] and dielectric inorganic compounds. [25,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Here, spatial phasematching is not required, as these ensemble materials consist of a large amount of randomly oriented crystallites, allowing for the observation of averaged SHG signals.…”

“…[25,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Here, spatial phasematching is not required, as these ensemble materials consist of a large amount of randomly oriented crystallites, allowing for the observation of averaged SHG signals. [18,25] These features allow their application, for example, in nano-and microphotonics, imaging, optical sensing/coding, biomedicine, and anti-counterfeiting. [1] Another potential NLO feature of materials is up-conversion photoluminescence (UC-PL), a nonparametric process resulting in the conversion of two or more lower-energy photons into a single higher-energy photon, which is typically realized in low-phonon energy inorganic, lanthanide (Ln)-doped polycrystalline micro-/nanosized particles.…”

Swallowed Embedding of Nanopetal-Rich Microflowers in Flexible Photocatalytic and Thermoresponsive Functional Composite Fibers

“…To date, it is still a great challenge to develop suitable strategies to optimize the separation rate of carriers and maximize the photocatalytic activity of BiOBr. − It has been demonstrated that the size and shape of photocatalysts have an impact on photocatalytic performance. − For example, a 2D nanosheet structure with a large specific surface area provides more reaction sites and thus promotes photocatalytic reactions. − Among the various shapes of BiOBr, − the flower-shaped microsphere structure of BiOBr enriched with nanosheets maximizes its specific surface area while promoting the adsorption of pollutants . In addition, doping rare earth ions into BiOBr is an effective way to enhance the separation efficiency of electron–hole pairs. − However, the rapid recombination of photogenerated carriers and the high surface energy of microspheres result in severe aggregation, thus imposing limitations on photocatalytic activity. − Assembling microspheres on fibers provides a feasible way to prevent agglomeration and facilitates recycling. − …”