Abstracts

Optically active luminescent materials, based on lanthanides attract significant attention due to their unique spectroscopic properties, non-linear optical (NLO) activity and possibility of application as contactless sensors, in anti-counterfeiting and optical coding. NLO spectroscopy may be a powerful tool for sensing of various intrinsic properties of materials and different state functions of the system. Materials exhibiting diverse non-parametric and parametric NLO processes, such as up-conversion luminescence (UCL) and second harmonic generation (SHG), respectively, are essential in areas such as nanophotonics, optical information processing, and biomedical imaging. However, the polycrystalline, micron- and nano-sized materials employed for such diverse applications to date are efficient only for one type of non-linear optical activity. Here we show the feasibility of simultaneous employing the luminescence of lanthanides, both down-shifting and/or UCL, combined with SHG in different polycrystalline materials, including micron- and nano-sized inorganic particles and metal-organic-framework (MOF) materials.^1-3 In the first case we used BaTiO₃:Ln³⁺ (Ln = Yb, Er, Ho) micron-sized powder for optical temperature sensing, following the thermal evolution of SHG and UC emission bands (intensity ratios). Moreover, we showed that this strategy can be utilized for detection of phase transitions from non-centrosymmetric to centrosymmetric systems, and vice versa.¹ In the case of Ln-doped MOF (Ln = Er³⁺ or Yb³⁺/Er³⁺) materials 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 ≈900-1025 nm, the materials also exhibit the NIR luminescence of Er³⁺ ions, centered at ≈1550 nm. Taking the benefits of different thermal responses of the mentioned effects, we have developed a non-linear optical thermometer based on the lanthanide-MOF materials. 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.² Finally, we developed the multi-modal, NLO active nanomaterials based on lanthanide-doped LiNbO₃ nanoparticles that simultaneously exhibit unprecedentedly efficient SHG and THG, as well as UC photoluminescence. These dielectric nanoparticles retain their high non-linear optical conversion efficiency both as powder and as aqueous colloidal solution. We used them for fabrication of optically active biocompatible microfibers and polymer-based 3D-printable objects, as well as for fingerprint detection. Finally, we demonstrate the first 8-bit coding platform purely based on multi-modal non-linear optical activity originating from different parametric and non-parametric processes, show-casing the technological potential of these materials for anti-counterfeiting and advanced optical information processing.^3References:[1] Zheng, T. et al. Advanced Optical Materials, 9, 2100386 (2021)[2] Runowski, M. et al. ACS Applied Materials & Interfaces 15, 3244–3252 (2023)[3] Runowski, M. et al. Advanced Functional Materials. 34, 2307791 (2024)