Precise knowledge about optical and structural performance of individual rare earth (RE)‐doped particles is extremely important for the optimization of luminescent particles and for fully exploiting their capability as multifunctional probes for interdisciplinary applications. In this work, optical and structural anisotropy of individual particles through RE‐doped single fluoride microcrystals with controllable morphology is reported. Unique luminescent phenomena, for example, white light‐emission from Pr3+ at single particle level and different photoluminescent spectra variation dependence on excitation polarization orientation at different excitation direction are observed upon excitation with a 980 nm linearly polarized laser. Based on the analysis of local site symmetry and electron cloud distribution of REs in hexagonal structure by density functional theory calculations, an exciting mechanism of excitation polarization response anisotropy is given for the first time, providing a guidance for emission polarization simultaneously. The structural anisotropy is presented in Raman spectra with obvious differing Raman curves, revealing the reason why there are differences between powder groups. Taking advantage of anisotropic crystals, potential applications in microscopic multi‐information transportation are suggested for the optical and structural performance anisotropy from RE‐doped fluoride single nano/microcrystals to ordered nano/microcrystal arrays, such as local rate probing in a flowing liquid.
One-dimensional (1D) metal halide perovskite nanowire (NW) arrays with high absorption efficiency, emission yield and dielectric constants, as well as anisotropic optoelectronic properties have found applications in energy harvesting, flexible electronics, and biomedical imaging devices. Here, a modified two-step solvothermal method is developed for the synthesis of self-assembled cubic CsPbBr 3 NW arrays. This method provides facile access to continuous and uniform ultrafine perovskite NWs and well-aligned pure perovskite NW arrayed architectures. Under excitation at 365 nm, the CsPbBr 3 NWs give a strong blue emission observable to the naked eyes. The CsPbBr 3 NWs also exhibit strong two-photon excited luminescence under the irradiation with an 800 nm pulse laser. By rotating the polarization angle of the 800 nm laser, strong polarization dependence with a polarization degree up to~0.49 is demonstrated in the selfassembled CsPbBr 3 NW array, although the CsPbBr 3 NWs have an isotropic cubic structure. Based on density functional theory (DFT) calculations, this polarization-dependent emission is correlated with the anisotropic charge density distribution of the perovskite NWs. These findings suggest that the ultrafine CsPbBr 3 NWs with a well-defined self-assembled architecture could be applied as next-generation polarizationsensitive photoelectronic detection materials.
All solid-state PbS quantum dot (QD)-doped glass precursor fibers avoiding crystallization during fiber-drawing process are successfully fabricated by melt-in-tube technique. By subsequent heat treatment schedule, controllable crystallization of PbS QDs can be obtained in the glass precursor fibers, contributing to broad near-infrared emissions from PbS QD-doped glass fibers. Nevertheless, we find that element-migration and volatilization of sulfur simultaneously happen during the whole fiber-drawing process, because of the huge difference between the melting temperature of core glass and the fiber-drawing temperature. Element-migration pathways along the fiber length were revealed. Such PbS QD-doped glass fiber with broadband emissions will be a potential application as gain medium of broadband fiber amplifiers and fiber lasers.
The key components in display, imaging, data communication, and photoelectric detection fields are low‐dimensional micro‐/nanomaterials with highly anisotropic optoelectronic properties manifesting polarized light. However, for anisotropic upconversion (UC) materials, obtaining tunable polarization characteristics remains a significant challenge. Herein, based on a detailed investigation of the crystal structure, local symmetry, and properties of rare‐earth ions (RE3+), the authors successfully realized a tunable UC light polarization characteristic (UCLPC) with dependence on excitation polarization using a series of RE3+ single‐ or co‐doped β‐NaYF4 microrods. By simulating the electron cloud distribution and bonding structure based on density functional theory calculations, it is shown that: i) Yb3+ with a unique electron cloud distribution adjusts the UCLPC of the activator via energy transfer processes; ii) co‐doping with RE3+ having a larger dipole polarizability improves the UCLPC of the activator by performing its electric field distribution toward anisotropy; and iii) increasing the activator concentration strengthens the UCLPC. By exploiting the unique UCLPC from different doping combinations, applications in optical storage, encryption, and anti‐counterfeiting are illustrated. Simultaneously, the findings obtained in this work will provide new and exciting fundamental insights into understanding the polarization properties of RE3+ in an anisotropic structure.
Due to the widely tunable band gap and broadband excitation, CdS quantum dots (QDs) show great promise for yellow‐light luminescence center in white‐light‐emitting devices. The light intensity of the CdS QD‐doped glass was enhanced by doping the Tm3+ ions due to the higher absorption rate. The influence of Tm3+ ions on the surface structure of CdS QDs was enormous according to the first‐principles calculations. Doping Tm3+ ions change the surface state of CdS QDs, which will fix the QDs emission peaks and enhance the luminescence of CdS QDs at a lower heat‐treatment temperature. White‐light emission was obtained by tuning the relative concentration between Tm3+/CdS QDs. However, there is a fundamental challenge to fabricate QD‐doped glass fibers by rod‐in‐tube method since uncontrollable QDs crystallization is hard to avoid. Herein, a white‐light‐emitting borosilicate glass fiber was fabricated by the “melt‐in‐tube” method using a special designed Tm3+/CdS QDs co‐doped borosilicate glass with low‐melting temperature as fiber core. After heat treatment, ideal white‐light emission was observed from the fiber under excitation at single wavelength (359 nm). This finding indicates that Tm3+/CdS QDs co‐doped glass fiber with white‐light‐emitting devices has potential application as gain medium of white‐light‐emitting sources and fiber lasers.
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