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

Abstract

Polarized upconversion luminescence (UCL) of lanthanide-doped micro/nano-crystals has shown great promise in single-particle tracking and super-resolution bioimaging. However, because of the spectral line broadening and multiple sites of lanthanide in upconversion particles (UCPs), the crystal-field (CF) polarization components of UCL are usually undistinguishable. Herein, we report the linearly polarized UCL in LiLuF 4 :Yb 3+ /Er 3+ single microcrystals with resolvable CF transition lines and a polarization degree up to 0.82. The CF levels and CF transition lines of Er 3+ , as well as their emission polarization anisotropy, are unraveled for the first time through low-temperature and high-resolution photoluminescence (PL) and UCL spectroscopies. By taking advantage of the well-resolved and highly-polarized CF transition lines of Er 3+ , we demonstrate the application of LiLuF 4 :Yb 3+ /Er 3+ single microcrystals as anisotropic UCL probes for orientation tracking. These findings provide fundamental insights into the polarization anisotropy of UCL in lanthanide-doped single particles, thus laying a foundation for the future design of anisotropic luminescent probes towards versatile applications.

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).…”

“…In this context, some other groups also reported the polarized UCL from NaYF 4 , LiYF 4 , and LiLuF 4 UCNPs. [ 107–111 ] To make use of polarized UCL, Paloma et al. reported using microsized upconverting particles (UCP) to monitor the suspending medium in real‐time via single‐particle spectroscopy.…”

Responsive Sensors of Upconversion Nanoparticles

“…Using an optical beam, one can further trap single LiYF 4 :Yb 3+ /Er 3+ microparticles in three different spatial orientations, which allowed for its polarized emission to be probed at two different angles, θ = 56° and 90°. Recently, the crystal-field (CF) polarization components of a class of bipyramidal LiLuF 4 :Yb 3+ /Er 3+ microcrystals with a mean size of ∼20 μm × 12 μm has been determined by SPPS . The resolved CF components include transitions from the 2 H 11/2 (515–530 nm), 4 S 3/2 (538–554 nm), and 4 F 9/2 (645–675 nm) multiplets to the 4 I 15/2 ground state of Er 3+ , corresponding to emission peaks with full-width at half-maximum less than 0.70 nm.…”

“…Recently, the crystal-field (CF) polarization components of a class of bipyramidal LiLuF 4 :Yb 3+ /Er 3+ microcrystals with a mean size of ∼20 μm × 12 μm has been determined by SPPS. 34 The resolved CF components include transitions from the Here I 1 and I 2 are the luminescence intensity from two thermally coupled energy levels, E 1 and E 2 , respectively. I 2 /I 1 follows Boltzmann distribution, C is a constant, ΔE is the energy gap between the two excited states, k B is the Boltzmann constant, and T is the absolute temperature.…”

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

“…Detection of the 3D orientation is critically important for applications, and the orientation tracing would be attractive for interaction and structural dynamics studies . There are now optical technologies for obtaining the 3D orientation, such as defocusing imaging , and fluorescence polarization microscopy. , Although polarized UC emission was observed, , the exact correlation between the polarization and the orientation of crystal has not been established. From the discussions presented above, the in-plane orientation of crystals can be obtained from θ p (Figure ).…”