Orthogonally Polarized Luminescence of Single Bismuth Phosphate Microcrystal Doped with Europium

Abstract

Rare‐earth‐doped micro/nanocrystals are significant candidates for nanophotonic and quantum information elements. Nevertheless, the polarization of light emission, which serves as one of the most widely adopted optical information carriers, has been rarely studied in such micro/nanocrystals due to the random crystalline orientation of the ensemble cluster as grown. Herein the polarization‐resolved spectroscopy on a single europium‐doped bismuth phosphate (BiPO4:Eu) microcrystal is performed, and a series of partially linearly polarized emission in the visible spectrum is observed, which can be grouped into orthogonal pairs. Such emission features are well explained by a phenomenological model of group theory that gives rise to the existence of optical C2 axes induced by local symmetry breaking. Such a polarization detection provides a neat optical method to distinguish single micro/nanocrystals from clusters, and confirms the tunable polarization features by selecting the suitable single microcrystal and engineering its orientation of crystalline axis. The rare‐earth‐doped single micro/nanocrystals, with precise positioning technique realized, can promisingly serve as controllable polarization devices on integrated photonic circuits.

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

“…The DOP is used to quantitatively evaluate the polarization state, which is given as: DOP = (I max − I min )/(I max + I min ), where I max and I min are the maximum and minimum integrated luminescence intensities, respectively. [21,22] The extracted DOP at 588, 591, 614, 616, 687, 693 nm are 0.873, 0.709, 0.850, 0.961, 0.891, and 0.486, respectively, which is much higher than that of other polarized emission materials. [22,[34][35][36][37][38][39] Such high anisotropic optical characteristics of Eu-BTC microrod can be attributed to the synergistic effect of both intrinsic anisotropic crystal structure and the lowsymmtry energy level splitting of Eu 3+ .…”

“…[21,22] The extracted DOP at 588, 591, 614, 616, 687, 693 nm are 0.873, 0.709, 0.850, 0.961, 0.891, and 0.486, respectively, which is much higher than that of other polarized emission materials. [22,[34][35][36][37][38][39] Such high anisotropic optical characteristics of Eu-BTC microrod can be attributed to the synergistic effect of both intrinsic anisotropic crystal structure and the lowsymmtry energy level splitting of Eu 3+ . [20] As shown in Figure 3b, the Eu 3+ center displays a point symmetry of C 4h and crystallizes in a chiral space group P4 1 22 that is seven-coordinated Adv.…”

“…[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.…”

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

“…We next discuss the mechanism of the highly polarized UC emission. From the effect of the crystal field, the split sub-energy levels lead to the multiple emissions of Ln 3+ , and the polarized character is decided by the symmetry of the crystal field. ,, For the tetragonal LiREF 4 (RE represents a rare earth ion), six RE 3+ ions, denoted 1–6, locate a symmetry of S 4 . As shown in Figure a, sites of 1, 4, and 5 and 2, 3, and 6 are oriented oppositely.…”

“…As shown in Figure a, sites of 1, 4, and 5 and 2, 3, and 6 are oriented oppositely. Interestingly, the C 2 axes of these two groups of sites are both aligned with the crystal; this leads to the highly polarized emissions as the C 2 axes are thought to be critical for a linear polarization. , …”