copy and easy to authenticate) is the primary approach for resisting the increasing sophistication of counterfeiting. [1] Due to their visual identifiability, colorful light emissions of luminophors are considered to be ideal security elements. The luminescent patterns of banknotes under ultraviolet (UV) excitation are a well-known sample of this approach. In addition to the spatial spectral fingerprints displayed in emission colors, the excitation mode and emission lifetime of luminescence can be used as authentication information, providing higher coding levels. For example, photoluminescence (PL), upconversion luminescence (UCL), and long-lasting luminescence (LLL) are three quintessential modes for anticounterfeiting and information security. [2] The PL mode produces photons at longer wavelengths than the excitation wavelength, for example, downshifting UV excitation to visible emission. [3] The UCL mode converts longwavelength photons to short-wavelength ones, for example, in the upconversion of near-infrared (NIR) excitation to visible emission. [4] It is important to note that PL and UCL phenomena will disappear immediately once light excitation is stopped, showing a feature of pulse duration (so-called fluorescence). In contrast, LLL shows delayed initiation after the cessation of Optical characteristics of luminescent materials, including emission color (wavelength), lifetime, and excitation mode, play crucial roles in data communication and information security. Conventional luminescent materials generally display unicolor, unitemporal, and unimodal (occasionally bimodal) emission, resulting in low-level readout and decoding. The development of multicolor, multitemporal, and multimodal luminescence in a single material has long been considered to be a significant challenge. In this study, for the first time, the superior integration of colorful (red-orange-yellowgreen), bitemporal (fluorescent and delayed), and four-modal (thermo-/ mechano-motivated and upconverted/downshifted) emissions in a particular piezoelectric particle via optical multiplexing of dual-lanthanide dopants is demonstrated. The as-prepared versatile NaNbO 3 :Pr 3+ ,Er 3+ luminescent microparticles shown are particularly suitable for embedding into polymer films to achieve waterproof, flexible/wearable and highly stretchable features, and synchronously to provide multidimensional codes that can be visually read-out using simple and commonly available tools (including the LED of a smartphone, pen writing, cooling-heating stimuli, and ultraviolet/ near-infrared lamps). These findings offer unique insight for designing highly integrated stimuli-responsive luminophors and smart devices toward a wide variety of applications, particularly advanced anticounterfeiting technology.

Color manipulation of intense multiluminescence from CaZnOS:Mn2+ has been realized by adjusting Mn2+ concentration. Not only the photoluminescence (PL) of Mn2+ emission from 4T1(4G) to 6A1(6S) shows a red shift from yellow to red with increasing Mn2+ concentration, which is in contrast to the fixed PL emission reported by Hintzen et al. (Chem. Mater., 2009), but also mechanoluminescence (ML) and cathodoluminescence (CL) have a similar variation. More attractively, the brightness of multiluminescence is surprisingly intense for all the CaZnOS:Mn2+ with a large-scale Mn2+ doping (0.1–10 mol %). Based on the investigation of crystal field, various spectral results, and PL lifetimes, the red-shift mechanism of multiluminescence reported here has been proposed to arise from the exchange interaction effect of Mn2+ pairs at higher concentrations. In addition to correcting the previous misunderstanding on the emission of CaZnOS:Mn2+, these findings extend the tunable emission window, opening up new opportunities in multifunctional applications of PL, ML, and CL involving multicolor light sources, displays, and stress imaging, especially providing a novel resolution to design ML colors.

No abstract

The structures of Si(n) (n = 2-33) were confirmed by genetic algorithm (GA)/tight binding (TB) search and ab initio calculations at the B3LYP/6- 311++G(2d) and PW91/6-311++G(2d) level, respectively. The fragmentation energies, binding energies, second differences in energy, and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps in the size range 2≤n≤33 were calculated and analyzed systematically. We extended the cluster size involved in the fragmentation analyses up to Si(33), and studied the multi-step fragmentations of Si(n). The calculated result is similar to the fragmentation behavior of small silicon clusters studied previously, showing that Si(6), Si(7), and Si(10) have relatively larger stabilities and appear more frequently in the fragmentation products of large silicon clusters, which is in good agreement with the experimental observations.

No abstract