Highly Polarized Upconversion Emissions from Lanthanide-Doped LiYF₄ Crystals as Spatial Orientation Indicators

Abstract

Polarized emission, an inherent characteristic that correlated with structure and morphology, is very sensitive to orientation. For the upconversion (UC) emission of lanthanides, the mechanism of polarization is rarely discussed, and the highly polarized UC emissions are poorly developed. Herein, with the benefit of the strong anisotropic crystal field, well-resolved emissions from lanthanide-doped LiYF 4 crystals were studied, and highly polarized UC emissions from Er 3+ and Ho 3+ were investigated. With multiple sub-energy level transitions, the UC emissions are classified into two sets, with transition dipoles being either parallel or perpendicular to the c-axis of the LiYF 4 crystal. An optical three-dimensional orientation sensor was further investigated, in which the in-plane angle is referenced from the orientation of the transition dipoles. In contrast, the out-of-plane angle can be deduced from the change in the degree of polarization. This research deepens our understanding of the polarized photoluminescence, and it opens up an avenue toward unique UC orientation sensors.

Molecular Cocrystals with Hydrogen-Bonded Polymeric Structures and Polarized Luminescence

“…Accordingly, the corresponding polarization emission profile yielded a fitted curve in the shape of the number “8”. The long axis of the fitted polarization emission profile was in accordance with the oriented direction of the molecular transition dipoles ( μ ) of the crystal under study [ 39 , 40 , 41 , 42 ]. In other words, when the electric field of the light was parallel to μ , the emission was the highest ( I max ), while the emission was the lowest ( I min ) when the electric field was vertical to μ .…”

“…The variation of the positions of the pyridine nitrogen atoms on the skeleton allows for the formation of hydrogen bonds between pyridinium protons and sulfonate anions in different directions. In addition, the polarized emission properties of organic crystals are highly dependent on the molecular arrangement, and those with consistent parallel or antiparallel molecular orientation generally display a high degree of emission polarization [ 39 , 40 , 41 , 42 ]. On account of the highly ordered binary molecular packing in two-component linear hydrogen-bonded polymers, the fabricated microcrystals are expected to display prominent polarized emissions.…”

Two-Dimensional Hybrid Perovskitoid Micro/nanosheets: Colorful Ultralong Phosphorescence, Delayed Fluorescence, and Anisotropic Optical Waveguide

“…Traditionally, obtaining linearly polarized light required the installation of bulky and rigid optical components such as polarizers, which increased the optical loss and limited its application. , Therefore, polarization-sensitive materials with inherent polarized photoluminescent emissions have gained tremendous attention. In this context, optical anisotropy is the cornerstone of polarized luminescence, as it can affect the light transmission and absorption properties, which is also closely correlated with crystallographic symmetry, morphology, or configuration. − Recently, the emerging 2D anisotropic materials became promising due to their intrinsic sensitivity to linearly polarized light. ,, However, 2D materials with high polarization anisotropy are still rare to date, particularly for combined short-lived and long-lived polarized emission in one system.…”

Tailoring Lanthanide Upconversion Luminescence through Material Designs and Regulation Strategies

“…In this context, some other groups also reported the polarized UCL from NaYF 4 , LiYF 4 , and LiLuF 4 UCNPs. [107][108][109][110][111] To make use of polarized UCL, Paloma et al reported using microsized upconverting particles (UCP) to monitor the suspending medium in real-time via singleparticle spectroscopy. [112] Single UCP was optically trapped and maintained at a certain position, followed by the excitation of linearly polarized 980 nm laser (Figure 10b).…”