RESUMEN
Thermochromic fluorescent materials (TFMs) characterized by noticeable emission color variation with temperature have attracted pervasive attention for their frontier application in stimulus-response and optical encryption technologies. However, existing TFMs typically suffer from weak PL reversibility as well as limited mild operating temperature and severe temperature PL quenching. PL switching under extreme conditions such as high temperature will undoubtedly improve encryption security, while it is still challenging for present TFMs. In this work, high-temperature thermochromic fluorescence up to 473 K and robust structural and optical reversibility of 80 cycles are observed in Rb2 MnBr4 (H2 O)2 and related crystals, which is seldom reported for PL changes at such a high temperature. Temperature-driven nonluminous, red and green light emission states can be achieved at specific temperatures and the modulation mechanism is verified by in situ optical and structural measurements and single particle transition. By virtue of this unique feature, a multicolor anti-counterfeiting label based on a broad temperature gradient and multidimensional information encryption applications are demonstrated. This work opens a window for the design of inorganic materials with multi-PL change and the development of advanced encryption strategies with extreme stimuli source.
RESUMEN
Optical gain in solution-processable quantum dots (QDs) has attracted intense interest toward next-generation optoelectronics; however, the development of optical gain in heavy-metal-free QDs remains challenging. Herein, we reveal that the ZnSe1-xTex-based QDs show excellent optical gain covering the violet to near-red regime. A new gain mechanism is established in the alloy QDs, which promotes a theoretically threshold-less optical gain thanks to the ultrafast carrier localization and suppression of ground-state absorption by the Te-derived isoelectronic state. Further, we disclose that the hot-carrier trapping represents the main culprit to exacerbate the gain performance. With the increase of Te-to-Se ratio, a sub-band-gap photoinduced absorption (PA) appears and extinguishes the optical gain. To overcome this issue, we modulate the inner ZnSe shell thickness, and the gain is recovered by reducing the overlap between the gain and PA regions in the Te-rich QDs. Our finding represents a significant step toward sustainable QD-based optoelectronics.
RESUMEN
A new beryllium-free zincoborate, BaZn3(BO3)2F2, with a KBBF-type structure has been synthesized for the first time. The electrostatic force of interaction in BaZn3(BO3)2F2 provides better linkage in neighboring [ZnBO3F]∞ single layers. BaZn3(BO3)2F2 is the first case of borates with both [ZnO3F] tetrahedra and [ZnO6] octahedra, enriching the structural chemistry of borate system. All the coplanar [BO3] triangles align in the same direction with a high density, which endows BaZn3(BO3)2F2 with a large birefringence of cal. 0.076 at 1064 nm. This work is of great significance to design beryllium-free borates with a KBBF-type structure.
RESUMEN
In virtue of the essential role in controlling polarized light, outstanding ultraviolet (UV) and deep-ultraviolet (DUV) birefringent crystals are imperative in many advanced optical instruments. To design the UV and DUV crystals with large birefringence, we paid more attention to combining the excellent gene, π-conjugated [BO3] unit and metal cations beneficial to blue-shift the cutoff edge; finally, two rare-earth borates Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 have been synthesized using the high-temperature solution method. Compared with Na3La2(BO3)3, Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 are isostructural, and the isolated [BO3] units are arranged nearly parallel to each other in the structure, which is conducive to generating a larger birefringence. The structural comparison between the two crystals and Na3La2(BO3)3 indicates that the various coordination environments of alkali metal cations play an important role in the evolution of the crystal structure from Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 to Na3La2(BO3)3. This work can contribute to a better understanding of the enhancement in birefringence from Na3La2(BO3)3 (0.023 @ 1064 nm) to Li3La2(BO3)3 (0.078 @ 1064 nm) with the perspective of structure-property relationships. Meanwhile, the two title crystals possess the DUV cutoff edge (<190 nm), suggesting that they can be applied as the DUV birefringent crystals.
RESUMEN
Accurate rainfall observation data with high temporal and spatial resolution are essential for national disaster prevention and mitigation as well as climate response decisions. This paper introduces a field experiment using an E-band millimeter-wave link to obtain rainfall rate information in Nanjing city, which is situated in the east of China. The link is 3 km long and operates at 71 and 81 GHz. We first distinguish between the wet and the dry periods, and then determine the classification threshold for calculating attenuation baseline in real time. We correct the influence of the wet antenna attenuation and finally calculate the rainfall rate through the power law relationship between the rainfall rate and the rain-induced attenuation. The experimental results show that the correlation between the rainfall rate retrieved from the 71 GHz link and the rainfall rate measured by the raindrop spectrometer is up to 0.9. The correlation at 81 GHz is up to 0.91. The mean relative errors are all below 5%. By comparing with the rainfall rate measured by the laser raindrop spectrometer set up at the experimental site, we verified the reliability and accuracy of monitoring rainfall using the E-band millimeter-wave link.
RESUMEN
Inspired by the strategy of fluorine introduction in borates and phosphates, the inorganic oxyfluoride (NH4)3[PO3F][BF4] with B-F and P-F bonds has been characterized as the first fluoroborate-fluorophosphate. The International Union of Pure and Applied Chemistry (IUPAC) name for (NH4)3[PO3F][BF4] should be ammonium tetrafluoroborate-monofluorophosphate according to the structure characteristics. The existence and coordination of fluorine in (NH4)3[PO3F][BF4] were confirmed by several approaches, including single-crystal structure analysis; bond valence analysis; and X-ray energy dispersive, infrared spectrum, and also nuclear magnetic resonance spectroscopy. This work is of great significance to enrich the solid-state chemistry of borates and phosphates and also open a new branch of mixed anion compound with fluoroborate-fluorophosphates.