Towards complete photonic band gap in a high refractive index nanoparticle-doped blue phase liquid crystal

Khatun, Nurjahan; Sridurai, Vimala; Nair, Geetha G.

doi:10.1039/d3nr03366j

Cited by 1 publication

(16 citation statements)

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“…The high-index NPs are considered to be Se NPs with a refractive index of 3.07 in the optical frequencies. 40 To begin with, the photonic band diagrams of pristine BPI, i.e., Pristine dye-doped BPLC (Δn = 0.04) and high-index NPs incorporated BPI, denoted as Se-dye-doped BPLC (Δn = 1.4), are simulated 22 with a point dipole placed inside the unit cell. The lattice parameter of the unit cell is optimized to obtain the band diagrams in the optical regime.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…The details of the calculations are provided in Section S1, Supporting Information. 22 The band diagram is also simulated for a homogeneous medium with Δn = 0 for comparison with those obtained for low and high Δn values. The DOS is extracted from the band diagrams using a histogram approach.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Se NPs (diameter ∼5 nm), the high-index particles of choice, capped with polyvinylpyrrolidone (PVP) (to facilitate uniform dispersion of NPs in the BPLC medium), are synthesized in the laboratory using the modified chemical reduction method, as reported in our previous publication. 22 The particles thus prepared are dispersed in the dye-doped-BPLC using the procedure described below. The chemical structures and phase transition temperatures of the different constituent compounds used in the preparation of the composites are given in Figure S2 and Section S2, Supporting Information.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…The concentration of the Se NPs is chosen to be 1 wt % as the PBG width is found to be maximum for this concentration. 22 For detailed explanation, see Section S4, Supporting Information. The Pristine dye-doped BPLC is prepared by adding a known quantity of Rhodamine B solution in ethanol to the host BPLC, and the components are heated to 80 °C and stirred continuously using a magnetic stirrer for ∼2−3 days to obtain a homogeneous mixture.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…35 In our earlier work, a simple and elegant method of incorporating high-index nanoparticles (NPs) into a BPLC is demonstrated to drive the BPI, otherwise an incomplete PBG system, toward a complete PBG. 22 The NPs (diameter ∼5 nm) that get confined inside the defect cores 38,39 (diameter ∼10 nm) effectively increase the refractive index of the disclination lines and hence Δn, leading to an enhanced PBG width.…”

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Effect of High-Index Nanoparticles on the Emission Properties of a Dye-Doped Blue Phase Liquid Crystal

Khatun,

Nair

2024

Chem. Mater.

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This study demonstrates a significant advancement in enhancing photoluminescence (PL) intensity by the inclusion of high-index dielectric nanoparticles into a dye-doped blue phase liquid crystal (BPLC). The blue phase I (BPI), the cubic subphase of the blue phase exhibited by highly chiral liquid crystals, is inherently an incomplete photonic band gap (PBG) system due to the low refractive index contrast Δn (<0.1). The Δn is given by the difference between the refractive indices corresponding to the double twisted cylinders and disclination lines that constitute the blue phases. Being an incomplete PBG system, BPI exhibits a narrow PBG width (2 to 3%), affecting the extent of enhancement in PL intensity in the dye-doped BPLC. An elegant pathway of confining highrefractive index selenium nanoparticles (n = 3.07 at optical frequencies) inside the core of disclination lines effectively increases the Δn (1.4) and thus the PBG width (6%), driving BPI toward a complete PBG. This, in turn, enhances the PL intensity by a factor of 3 when compared to the pristine BPLC, as demonstrated by finite element method simulations and reflection spectroscopy experiments. The simulations reveal that the efficient confinement of electromagnetic waves by the high-index nanoparticles leads to increased density of states (DOS) at the band edges, and hence, the enhanced emission. However, the emission gets suppressed at PBG as the DOS is nearly zero at the band gap. The in situ modulation in PL intensity is experimentally established utilizing thermally induced PBG tunability. Simulations also suggest that the enhancement in PL intensity strongly depends on the orientation and position of the dipole (dye) within the photonic cavity. Thus, incorporating high-index nanoparticles in the dyedoped BPLC enhances PL intensity, rendering the system more conducive for various optoelectronic applications such as lightemitting diodes and light-emissive displays.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

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confidence: 99%

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