A single nanophotonic platform for producing circularly polarized white light from non-chiral emitters

Abstract

Direct manipulation of light spin-angular momentum is desired in optoelectronic applications such as, displays, telecommunications, or imaging. Generating polarized light from luminophores avoids using optical components that cause brightness losses and hamper on-chip integration of light sources. Endowing chirality to achiral emitters for direct generation of polarized light benefits from existing materials and can be achieved by chiral nanophotonics. However, most chiral nanostructures operate in narrow wavelength ranges and involve nanofabrication processes incompatible with high-throughput production. Here, a single nanophotonic architecture is designed to sustain chiroptical resonances along the visible spectrum. This platform, fabricated with scalable soft-nanoimprint lithography transfers its chirality to conventional emitters (CdSe/CdS nanoplatelets, CdSe/CdS quantum dots, CsPbBr₃, CsPbI₃ perovskite nanocrystals and F8BT) placed atop, achieving a high dissymmetry emission factor (g_lum > 1). The dynamics study suggests enhanced out-coupling efficiency for one helicity by the photonic structure. Finally, a white light-emitting blend containing different emitters shows simultaneous dissymmetric emission values along the visible spectrum with this chiral nanophotonic platform.

Fig. 1. Universal nanophotonic platform for chiral light-matter interactions.

a Illustration of the chiral nanophotonic platform fabrication using soft-nanoimprint lithography and the geometrical parameters. b Low magnification scanning electron microscopy of the TiO₂ triskelion chiral metasurface. Scale bar: 2 μm. The inset shows the unit cell of the chiral platform. c Differential circularly polarized ballistic transmittance for both enantiomorphic metasurfaces exhibiting chiral resonances along the entire visible range. Shaded colored areas indicate the different spectral regions for probing emitting nanomaterials. Net optical chirality density for an L-triskelion at the resonant wavelengths of (d) λ₁ = 449 nm (e) λ₂ = 555 nm (f) λ₃ = 667 nm and (g) λ₄ = 700 nm.

Fig. 2. Conventional emitters for broadband chiral light-emission.

The morphological and optical properties of the different materials used to probe the chiral nanophotonic platform. a scanning electron microscopy of L-triskelion chiral metasurfaces coated with, from left to right, CdSe/CdS core-crown nanoplatelets, CsPbBr₃ perovskite nanocrystals, conjugated polymer F8BT, CdSe/CdS core-shell quantum dots and CsPbI₃ perovskite nanocrystals. Scale bar: 1μm (b) macroscopic picture of the large-area coated metasurface under UV light exposure. Scale bar: 4 mm (c) normalized photoluminescence spectra covering the entire visible range.

Fig. 3. Steady-state chiral photoluminescence in the visible range.

Circularly polarized photoluminescence for L- and R-triskelion chiral metasurfaces coated with CdSe/CdS core-crown NPLs (a, f), CsPbBr₃ PNCs (b, g) conjugated polymer F8BT (c,h) CdSe/CdS core-shell QDs (d, i) and CsPbI₃ PNCs (e, j), respectively. k–o dissymmetry emission factor g_lum for the corresponding emitting material for both enantiomorphic chiral metasurfaces. Inset: Macroscopic image of the metasurface coated with different emitters. SEM image of L- (a) and R-triskelion (f) metasurfaces.

Fig. 4. Into the dynamics of CdSe/CdS quantum dots chiral emission.

a Circularly polarized emission of L-triskelion chiral metasurface coated with CdSe/CdS QDs excited with an unpolarized LED source. Inset: 3D schematics of enhanced light-extraction efficiency for one circular polarization. b Circularly polarized emission of L-triskelion chiral metasurface coated with CdSe/CdS quantum dots excited with laser source. Inset: Laser source used for excitation c Stacked dissymmetry emission factor g_lum for a series of power densities for L- (solid) and R-triskelion (dashed). d normalized time-resolved chiral photoluminescence for L-triskelion CdSe/CdS quantum dots coated metasurface.

Fig. 5. Chiral white-light emission with a single nanophotonic platform.

Circularly polarized emission of white light for (a) unpatterned (b) L- and (c) R-triskelion metasurfaces. a Inset: white-light emissive mixed solution. d Dissymmetry emission factor g_lum for the chiral white-light emission of L- (solid red), R-triskelion (solid blue) and unpatterned (solid dark). e Scanning electron microscopy of the deposited material on the L-triskelion chiral metasurface. Scale bar: 500 nm. CIE diagram for both circularly polarized emissions of (f) L-and (g) R-triskelion metasurfaces. Inset: Scanning electron microscopy image of L-(f) and R-triskelion (g) metasurfaces.