Biodegradable Laser Arrays Self‐Assembled from Plant Resources

Abstract

The transition toward future sustainable societies largely depends on disruptive innovations in biobased materials to substitute nonsustainable advanced functional materials. In the field of optics, advanced devices (e.g., lasers or metamaterial devices) are typically manufactured using top‐down engineering and synthetic materials. This work breaks with such concepts and switchable lasers self‐assembled from plant‐based cellulose nanocrystals and fluorescent polymers at room temperature and from water are shown. Controlled structure formation allows laser‐grade cholesteric photonic bandgap materials, in which the photonic bandgap is matched to the fluorescence emission to function as an efficient resonator for low threshold multimode lasing. The lasers can be switched on and off using humidity, and can be printed into pixelated arrays. Additionally, the materials exhibit stiffness above typical thermoplastic polymers and biodegradability in soil. The concept showcases that highly advanced functions can be encoded into biobased materials, and opens the design space for future sustainable optical devices of unprecedented function.

Circularly Polarized Laser with Chiral Nematic Cellulose Nanocrystal Cavity

“…A clear transition at the threshold of 13 mJ cm –2 is found, above which a linear increase of the output intensity is measured in the light-out vs light-in data, as well as a sharp decrease of the spectral line-width (Figure e), strongly supporting the occurrence of laser emission. The CNC/SB-2 film displays a minimum FWHM of 9 nm, indicative of multimode lasing, likely due to the overlap of various emission peaks arising from local PBG dissimilarity of the CNC structure within the area of the excitation spot, as also observed in another report . Indeed, spatially resolved spectra of the film measured by laser confocal fluorescence microscopy show a variation of the emission spectra over areas of the order of tens of micrometers (SI Figure S9), which is attributable to the local pitch distribution of the chiral nematic CNC domain.…”

“…The SB (molecular structure in SI Figure S2) displays an absorption band centered at a wavelength of 350 nm and emission in the 400–600 nm range, with a peak wavelength at 444 nm in water (Figure a). To maximize the coupling efficiency and enable laser emission with a low threshold in photonic crystals, the PBG should resonate well with the SB emission. − In our system, the optical properties of the composite films are tailored by controlling the CNC helix pitch while keeping constant the SB concentration (0.7 wt %). It is well-known that sonication is a straightforward tool to manipulate the helix pitch .…”

“…Such self-assembled CNCs retain a helix structure also at the solid-state (i.e., after water evaporation), which can be regarded as a one-dimensional photonic crystal. , When the light propagates along the direction parallel to the helix axis of CNCs, a selective reflection band occurs, which is also known as a photonic bandgap (PBG) for left-handed CP (L-CP) light. Attempts to explore the intriguing chiral nematic structures of CNCs have led to materials presenting passive and active CP light. − Walther and co-workers recently reported the laser emission arising from assembling CNCs and a dye in a polymer matrix, however, the requirement to synthesize the dye-modified copolymer complicates the preparation process of the CNC-based laser array. Furthermore, the CNC-based materials act as a photonic structure cavity for the laser emission, and the advantage of the chiral structure is not exploited.…”

Homeotropic Concentric Helix Orientations in Chiral Nematic Cellulose Nanocrystal Films by Local Magnetic Fields

“…[16,17] Chiral nematic CNC materials are expected to play important roles in applications including sensing, security, and light management. [18][19][20][21][22][23][24][25][26] The lefthanded chiral nematic structures of CNC films enable selective reflection of left-handed circularly polarized (LCP) light and transmission of right-handed circularly polarized (RCP) light, and transform spontaneous luminescence to RCP luminescence on the film plane surface due to the underlying 1D Many fascinating device applications of chiral nematic materials are determined by their helical axis orientations. Cellulose nanocrystals (CNCs) self-assemble producing left-handed chiral nematic films with predominant planar textures.…”

“…[ 16,17 ] Chiral nematic CNC materials are expected to play important roles in applications including sensing, security, and light management. [ 18–26 ] The left‐handed chiral nematic structures of CNC films enable selective reflection of left‐handed circularly polarized (LCP) light and transmission of right‐handed circularly polarized (RCP) light, and transform spontaneous luminescence to RCP luminescence on the film plane surface due to the underlying 1D photonic bandgaps. [ 27–29 ] The circular polarization ability of the left‐handed chiral nematic CNC films has been extended to enable optically ambidextrous reflection and luminescence by post processing or synergistic self‐assembly and kinetic stabilization.…”