Near‐IR‐Sensitive Upconverting Nanostructured Photonic Cellulose Films

Abstract

1 of 7) 1600514 through a process known as photon upconversion. [27] Several materials are known that show energy transfer upconversion such as lanthanide-doped nanoparticles and complexes of organic-lanthanide, metal tetraphenylporphyrin, and metal polypyridyl hybrids. [8,[28][29][30] UC nanoparticles (UCNPs), particularly lanthanide-doped NaYF 4 , generally comprise an insulating inorganic host and lanthanide ion dopants homogeneously distributed in the host lattice. [31] UC nanocrystals can efficiently convert infrared light to visible light through lanthanide doping owing to distinct energy transfer pathways caused by dopant-host interactions. [32] The most promising UC luminescent nanomaterial is the hexagonal NaYF 4 phase, due to its unusually high UC quantum yield. [33] Such UC nanomaterials are ideal for use as photon UC emitters for a range of potential applications in security labeling, fingerprint identification, displays, lasers, and photodynamic therapy. [34,35] The selective coupling of semiconductors (e.g., TiO 2 , CdSe, P3HT) to lanthanide-doped NaYF 4 at the nanoscale can expand their useful application to photocatalysis and photovoltaics. [36][37][38] Self-assembly of nanosized UC units into photonic chiral nematic CNC films is anticipated to be a promising strategy for fabricating new materials due to their complementary optical properties. [39][40][41] Some empirical approaches have been recently used to prepare upconverting cellulose nanocomposites. Notably, Landfester and co-workers [42] performed microemulsion assembly to confine platinum(II) tetraphenylporphyrin UC emitters in cellulose nanofibrils. Merkoc and co-workers [43] used cellulose nanofibrils as a support for NaYF 4 :Yb,Er UCNPs. These materials found useful applications as chemical and optical sensing nanopapers, but these phases serve as achiral hosts for co-assembly and do not show photonic properties. Therefore, the fabrication of upconverting photonic papers with chiral nematic nanostructure still remains a challenge.Herein, the aim of our investigation was a systematic investigation of co-assembly of well-defined NaYF 4 :Yb,Er hexagonal nanorods with cellulose nanocrystals to yield new upconverting chiral nanomaterials, giving unprecedented optical properties. Combining polyvinyl alcohol-stabilized UCNP guests with chiral CNCs in high weight fraction resulted in nanocomposite films that display long lifetime of NIR-photoresponsive emission dopant in chiroptical matrix.NaYF 4 UC nanocrystals co-doped with 20 wt% Yb 3+ and 2 wt% Er 3+ were prepared by hydrothermal reaction of a basic mixture of rare earth nitrates and sodium fluoride as precursors, and oleic acid (OA) as a stabilizing agent in a mixture of water and ethanol. [44] Infrared (IR) and thermogravimetric (TGA) analyses ( Figure S1, Supporting Information) confirmed UCNPs were surface-capped by ≈9 wt% OA. We first examined the combination of the as-made UC particle colloids with CNC aqueous suspension. The resulting mixture phase-separated

The Self‐Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance

“…This has been demonstrated with zwitterionic surfactants, neutral or anionic polymers, amino resins or sol–gel precursors, and crosslinked latex nanoparticles . The cholesteric arrangement of CNCs can also accommodate small nanoparticles without disruption of the phase, e.g., plasmonic gold nanorods, allowing complex chiroptical effects …”

“…Beyond the aesthetic, the unique ability to reflect only a specific polarization of light at a precise wavelength band is beneficial for anticounterfeiting applications (Figure ). Such features can be further diversified by producing micro‐ and macroscale patterning (e.g., using temperature, compression, swelling, magnetic field orientation, or via additional CNC‐based depolarizing coatings) or integration of optically active dopants such as: upconverting or luminescent dyes or nanoparticles . Finally, since the underlying nanostructure defines the reflected color, a structural response (e.g., swelling) to an external stimulus allows for the design of cheap, biodegradable optical sensors.…”

Modulated Visible Light Upconversion for Luminescence Patterns in Liquid Crystal Polymer Networks Loaded with Upconverting Nanoparticles

“…[1][2][3][4][5][6][7][8][9] In general, lanthanide-doped UCNPs are dilute guest−host systems where trivalent lanthanide ions are dispersed as a guest in an appropriate dielectric host lattice. [1][2][3][4][5][6][7][8][9] In general, lanthanide-doped UCNPs are dilute guest−host systems where trivalent lanthanide ions are dispersed as a guest in an appropriate dielectric host lattice.…”

“…First, to obtain narrow size distribution, good crystallinity, and high fluorescence efficiency, UCNPs were synthesized Lanthanide-doped upconversion nanoparticles (UCNPs) have recently gained much attention in the field of displaying, detection, bioimaging, anticounterfeiting, and patterning due to their unique luminescent properties of converting near-infrared (NIR) light to shorter wavelength radiation. [1][2][3][4][5][6][7][8][9] In general, lanthanide-doped UCNPs are dilute guest−host systems where trivalent lanthanide ions are dispersed as a guest in an appropriate dielectric host lattice. [10] Diverse colors and luminescence intensity of UCNPs are known to be tuned by varying materials composition, phase structure, and laser power.…”

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

“…Past decades are characterized by the explosive development of technologies based on optoelectronics and photonics . The modern elemental base of these technologies includes refractive, diffraction and optical fiber components.…”