Abstract
Luminescent nanocomposite films, containing SrF2:Ho up-conversion particles, were prepared by two different protocols from aqueous dispersions of TEMPO-oxidized cellulose nanofibrils (TOCNF) functionalized with 3-aminopropyltriethoxysilane (APS) without the use of organic solvents at pH = 4.0–4.5 and 9.0–9.5, respectively. Proposed synthetic protocols included the formation of the films by drying the dispersions containing pre-hydrolyzed APS adsorbed onto TOCNF and SrF2:Ho particles followed by heating at 105 °C. Hydrophobic (water contact angle 101 ± 2°), strong, and translucent TOCNF/SrF2:Ho-APS films were prepared by casting from a solution at pH = 4.0–4.5. Scanning electron microscopy, energy-dispersive X-ray spectroscopy with element mapping, Fourier-transform infrared spectroscopy, X-ray diffraction methods confirmed homogeneous distribution of up-conversion particles in TOCNF matrices as well as the grafting of linear polysiloxanes via the condensation of silanol groups and OH-groups on the surface of TOCNF. Differential scanning calorimetry and thermogravimetry data confirmed an increase in thermal stability of the APS modified nanocomposite films obtained at pH = 4.0–4.5. Hydrophobic TOCNF/SrF2:Ho-APS nanocomposite films exhibited an intense red luminescence in the visible spectrum range (5I7 level excitation of Ho3+ ions with 1912 nm laser irradiation) as well as two-times higher laser damage threshold compared to unmodified TOCNF/SrF2:Ho films. TOCNF/SrF2:Ho-APS films can be used for visualization 2 μm laser radiation in medicine and long-distance atmosphere monitoring.
Highlights
IntroductionNew generation luminescent nanocellulose-based composites and hybrid materials have found numerous application in optoelectronics (Dias et al 2020; Vicente et al 2018; Yang et al 2018), organic light-emitting diodes (OLEDs) (Zhang et al 2019), biosensors and detectors for monitoring environment and/or food quality control (Dai et al 2020; Wang et al 2020), biomedicine (Guan et al 2018), latent finger print detection (Hai et al 2018), anti-counterfeiting applications (Li and Hu 2019; Xiong et al 2019; Zhang et al 2018) and some other areas of photonics (Eichhorn 2018; Lizundia et al 2020; Xue et al 2018; Zhang et al 2017)
Hydrophobic TEMPO-oxidized cellulose nanofibrils (TOCNF)/SrF2:Но-APS nanocomposite films exhibited an intense red luminescence in the visible spectrum range (5I7 level excitation of Ho3+ ions with 1912 nm laser irradiation) as well as two-times higher laser damage threshold compared to unmodified TOCNF/SrF2:Но films
The colloidal stability was ensured by electrostatic repulsion of COO– functional groups: both TOCNF chemical structure and selective oxidation of primary hydroxyls at С6 are well described in the literature (Okita et al 2010)
Summary
New generation luminescent nanocellulose-based composites and hybrid materials have found numerous application in optoelectronics (Dias et al 2020; Vicente et al 2018; Yang et al 2018), organic light-emitting diodes (OLEDs) (Zhang et al 2019), biosensors and detectors for monitoring environment and/or food quality control (Dai et al 2020; Wang et al 2020), biomedicine (Guan et al 2018), latent finger print detection (Hai et al 2018), anti-counterfeiting applications (Li and Hu 2019; Xiong et al 2019; Zhang et al 2018) and some other areas of photonics (Eichhorn 2018; Lizundia et al 2020; Xue et al 2018; Zhang et al 2017). Cellulose nanofibrils (CNF), cellulose nanocrystals (CNC) and TEMPO-oxidized CNF (TOCNF) are unique matrices for the synthesis of luminescent nanocomposites because of their large surface areas, high reactivities, good optical properties, mechanical strength and colloid stability (De. France et al 2020; Kontturi et al 2018; Thomas et al 2018). Metal fluorides are conside red most effective luminophore matrices because of low phonon energies and high probabilities of the anti-Stokes transitions allowing visualization of IR- irradiation (Fedorov et al 2011). % NaYF4:Yb:Er cubic phase was used for chiral up-conversion luminescent films preparation by evaporation-induced self-assembly (EISA) technique (Jiang et al 2016). Up-conversion luminescent films, retaining tunable photonic chiral activity, have been obtained by self-assembly of CNC and polyvinyl alcohol (PVA)-stabilized hexagonal
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