Linearly Polarized Emission from Shear-Induced Nematic Phase Upconversion Nanorods

Abstract

Lanthanide-doped particles exhibit unique polarization-dependent luminescence due to the anisotropic crystalline local symmetry surrounding the emitter. Precise control of the orientation of particles shows great significance for exploiting the luminescent polarization and their potential applications. Here, we demonstrated a facile polypropylene-aided shear-driven method to obtain large-scale orientationally ordered upconversion nanorods, showing a liquid-crystalline nematic phase. Upconversion nanorods with low aspect ratios were well-aligned with the crystalline c-axis along the shearing direction using monodispersed colloid nanorods as the nanoink. The order parameter of aligned upconversion nanorods can reach up to 0.95. The nematic upconversion nanorods demonstrated strong polarization-dependent luminescence with the high degrees of polarization of the 4 F 9/2 sublevels at 657 and 661 nm being 0.47 and 0.59, respectively. Taking advantage of these mesoscopic well-aligned upconversion nanorods, their peculiar polarized emissions are potentially useful for some interdisciplinary applications such as polarization-sensitive bioprobes and anticounterfeiting.

Polarized Electroluminescence Emission in High‐Performance Quantum Rod Light‐Emitting Diodes via the Langmuir‐Blodgett Technique

“…We also measured the rotational angle‐dependent PL measurements with the linear polarizer; the dependence of the peak PL intensity with respect to the rotational angle of the linear polarizing filter (θ p ) from 0° to 180° shows the typical behavior of polarized light. [ 16,30,43 ] As shown in Figure 2c, the normalized PL peak intensity is maximum when the polarizer is parallel to the alignment of QRs (θ p = 0°), and then gradually decreases with an increasing rotational angle until the polarizer is normal to the alignment of QRs (θ p = 90°). This behavior is not observed in the randomly oriented QR film deposited by the SC method (Figure S5, Supporting Information).…”

“…[ 35,38,39 ] Also, the LB technique transfers a highly dense monolayer film onto a substrate at each immersion or emersion step, thereby enabling precise thickness control at a monolayer level. Furthermore, the LB technique does not require any assisting matrix materials, such as liquid crystal polymer (LCP) for the photo‐assembly method [ 21,40 ] or thixotropic gel for the mechanical shearing assembly method; [ 30 ] the aligned QR film can be solely incorporated into the standard LED structure without containing any poorly conductive materials that hinder efficient charge carrier injection. Additionally, the lack of need for pre‐treatment on a substrate and low material consumption are additional beneficial features of the LB technique.…”

“…This is due to the difficulty in aligning QRs, particularly when employed as an emitting layer in a QR‐LED structure. Several methods have been attempted to align QRs, such as self‐assembly, [ 19,26,27 ] electric or magnetic field induced assembly, [ 28,29 ] mechanical shearing or stretching‐induced assembly, [ 16,30,31 ] and photo‐induced assembly. [ 21,26,32 ] These methods, however, produce limited QR alignment and, more importantly, are not compatible with the standard QR‐LED fabrication process.…”

Polarized upconversion luminescence from a single LiLuF4:Yb3+/Er3+ microcrystal for orientation tracking

“…Micropolarized spectroscopy that focuses on the luminescence of single lanthanide (Ln 3+ )-doped upconversion particles (UCPs) or their assemblies has recently attracted great attention, not only for its fundamental scientific importance but also because of its potential applications in diverse areas such as microscopic information transportation, microfluidics, single-particle tracking, and super-resolution bioimaging [1][2][3][4][5][6][7][8][9][10]. In contrast to anisotropic emitters such as semiconductor nanowires, quantum rods, and nanoplates that exhibit size-and shape-dependent polarized luminescence [11][12][13][14], Ln 3+ -doped UCPs show distinguished nature of emission polarization which is independent of the particle size and morphology [15][16][17][18][19].…”

Polarized Emission of Lanthanide Metal–Organic Framework (Ln‐MOF) Crystals for High‐Capacity Photonic Barcodes

“…[17][18][19] Although lanthanide ions have the capability in splitting of the energy levels by the crystal-field effect, [8,13,20] optical measurements are mostly performed on thin film or powder forms of lanthanide materials with random orientations, [8,13] thus commonly generating unpolarized emission. Meanwhile, the linearly polarized emission has been observed in the various lanthanide crystals or lanthanide doped micro/nanocrystals with appropriate site symmetries, [21,22] however, the emission efficiency and obtained degrees of polarization (DOP) of such inorganic lanthanide materials are still unsatisfactory. Ln-MOFs crystals with unique anisotropic arrangements are believed to possess higher emission efficiency and greater DOP due to the so-called antenna effect and superior asymmetric crystal structures, [8,13,23,24] which can potentially endow more stable and accurate spectroscopic encoding upon polarization modulation.…”