RESUMEN

A series of x%Ho3+, 5 %Tm3+, y%Yb3+:Bi2WO6 (x = 0, 0.5, 1, 3, 5; y = 0.5, 1, 3) luminescent materials was prepared using a high-temperature solid-phase method. The microstructure, up-conversion luminescence, and temperature sensing properties of the synthesized powders were analyzed. X-ray diffraction patterns revealed that doping with Ho3+, Tm3+, and Yb3+ ions at certain concentrations did not affect the orthorhombic crystal structure of the Bi2WO6 host. Scanning electron microscopy revealed that the morphology of the sample consisted of lumpy particles with a particle size range of 1-5 µm and agglomeration. SEM mapping and energy-dispersive X-ray spectroscopy analyses revealed that each element was relatively uniformly distributed on the particle surface. Under 980 nm excitation (380 mW), the strongest luminescence of the sample was obtained when both Ho3+ and Yb3+ doping concentrations were 1 %. Compared with the luminescence of the 5 %Tm3+ and 1 %Yb3+:Bi2WO6 sample, with increasing Ho3+ concentrations, the luminescence intensity of Tm3+ was first enhanced and subsequently weakened, whereas the luminescence of Ho3+ was significantly weakened, which indicates the positive energy transfer from Ho3+ â†’ Tm3+. At 980 nm (80-380 mW), for the 1 %Ho3+, 5 %Tm3+, and 1 %Yb3+:Bi2WO6 sample, the 538 nm, 545 nm, 660 nm, and 804 nm emission peaks originated from the two-photon absorption. FIR660 nm/804 nm, FIR545 nm/804 nm, and FIR538 nm/804 nm were used to characterize the temperature and corresponded to temperature sensitivities Sr of 0.0046 K-1, 0.022 K-1 and 0.024 K-1 at 573 K, respectively. At 498 K, the minimum temperature resolution δT values were 0.03384 K, 0.03203 K and 0.04373 K. When the temperature increased from 298 K to 573 K, the powder sample luminescence gradually shifted from the yellow-green region to the red region. The results of environmental discoloration and thermochromic performance tests indicate that this sample has potential application in optical anti-counterfeiting. FIR804 nm /660 nm and FIR804 nm /538 nm were obtained for the 40 NTU turbidity suspension under identical excitation conditions. At 298 K, for the 40 NTU turbidity sample, the maximum Sr values were 0.0197 K-1 and 0.0405 K-1; at 340 K, the minimum temperature resolutions δT values were 0.54037 K and 0.66237 K. When the temperature decreased from 340 K to 298 K, the luminescence of the 40 NTU suspension samples gradually shifted from the yellow region to the green region.

RESUMEN

Paper-based cultural relics constitute a significant and invaluable part of human civilization and cultural heritage. However, they are highly vulnerable to environmental factors such as ultraviolet (UV) photodegradation and acidification degradation, posing substantial threats to their long-term preservation. Carbon quantum dots (CQDs), known for their outstanding optical properties, high water solubility, and good safety, offer a promising solution for slowing down UV damage and acidification of paper-based relics during storage and transportation. Herein, we propose a feasible strategy for the simple preparation of CQDs with high dispersion stability, excellent UV absorption, room-temperature phosphorescence, and photostability for the safety protection of paper. Accelerated aging experiments were conducted using UV and dry-heat aging methods on both CQD-protected paper and unprotected paper, respectively, to evaluate the effectiveness of CQD protection. The results demonstrate a slowdown in both the oxidation and acid degradation processes of the protected paper under both UV-aging and dry-heat aging conditions. Notably, CQDs with complex luminescence patterns of both fluorescence and room-temperature phosphorescence also endue them as enhanced optical anticounterfeiting materials for multifunctional paper protection. This research provides a new direction for the protection of paper-based relics with emerging carbon nanomaterials.

RESUMEN

In mixed Sn-Pb perovskites, the synergistic properties of tin (Sn) and lead (Pb) are leveraged, effectively combining the merits of Pb-based perovskites while simultaneously reducing Pb-associated toxicity. However, the propensity for Sn to undergo facile oxidation from Sn2+ to Sn4+ poses a significant challenge to the stability of these mixed perovskites, limiting their advancement. This study proposes an innovative acetic acid (HAc)-driven synthesis approach to obtain a stable chain-like MAPb0.5Sn0.5Br3 nano-assembly. Leveraging the acidic properties of HAc serves a dual purpose. Primarily, it curtails the oxidation of Sn2+ to Sn4+. Secondly, it orchestrates nanocrystals (NCs) into a more uniform and ordered chain-like assembly, a consequence of hydrogen bonding and coordination interactions facilitated by the HAc. Additionally, HAc demonstrates its capability to passivate MAPb0.5Sn0.5Br3 surface through coordination bonding with unsaturated sites (i.e., Sn2+ or Pb2+), thus effectively compensating for bromide vacancies. Introducing HAc during the synthesis process yields perovskite NCs with enhanced thermal resilience, optical and water stability. Drawing upon the different stimulus responses of synthesized perovskite NCs when exposed to external environment, the optical anti-counterfeiting labels are prepared. The findings provide a potent strategy for augmenting the stability of perovskite NCs, suggesting their potential applicability in anti-counterfeiting endeavors.

RESUMEN

Humidity-responsive materials offer a promising approach to achieving tunable metasurface systems due to their fast and reversible swelling responses to moisture, which enables many important applications, such as real-time humidity sensing, optical switches, dynamic displays, and optical information encryption. However, the humidity-responsive structural coloration generally cannot provide a high spatial resolution and requires a complex patterning process. Here, we present a scalable moisture-driven color-changing Fabry-Pérot (FP)-like cavity composed of a polyvinyl alcohol layer sandwiched between an upper gold nanoparticles assembly and a bottom gold mirror. Through nanoparticle contact printing, we pixelated these cavities with sub-micrometer sizes without crosstalk and achieved an ultrahigh display resolution of ∼400 nm. Meanwhile, these nanoparticle-based FP (NBFP) cavities exhibit more vibrant colors than those of conventional film-based ones due to broadband absorption of the disordered nanoparticle assembly. Moreover, the NBFP cavities exhibit a rapid response (<300 ms), benefiting from the membrane pores formed in the gaps between the adjacent nanoparticles. Finally, we demonstrated the applications of the NBFP cavities in optical anti-counterfeiting and dynamic multi-color printing. These results suggest that our approach will help to realize a colorful, fast, and ultrahigh-resolution dynamic display device in optical security and colorimetric sensing.

RESUMEN

Cesium lead halide perovskite quantum dots (QDs) have attracted immense attention for luminescent materials due to their narrow emission bands and color-tunable emission. However, indispensable surface ligands originating from ligand-assisted synthesis strategies severely deteriorate the stability and luminescence properties of QDs since these ligands have a highly dynamic binding. Herein, we used a green fluorescence BODIPY molecule containing thiol (named SH-BDP) to regulate the CsPbBr3 QDs surface by ligand regulation. Density functional theory calculations proved that the SH-BDP molecule could bind to the exposed Pb of CsPbBr3 QDs stronger than traditional ligands to form stable SH-BDP-QDs. Moreover, the SH-BDP fixed on the CsPbBr3 QDs surface can improve water and light resistance. It also served as a knob to tune their luminescence properties and the reversible thermal-stimuli response. Finally, the multi-response property of SH-BDP-QDs was realized under polar solvent or heat along with UV light. In addition, we used the SH-BDP-QDs to create various anti-counterfeiting labels; several luminous modes were achieved under different external stimuli, which improved the quality of the optical anti-counterfeiting labels and ensured information security. This work indicates the immense potential of surface ligand manipulation in improving the stability and multi-stimuli-responsive optical encoding of perovskite quantum dots.

Asunto(s)

Plomo , Compuestos de Sulfhidrilo , Ligandos , Solventes , Agua , Cesio

RESUMEN

Sm3+ and Ce3+ singly doped and Sm3+ and Ce3+ co-doped Sr3B2O6 phosphors are prepared via a high-temperature solid-state reaction method. The crystal structure and phase purity are characterized by X-ray diffraction (XRD) analyses. The Sm3+-doped sample displays an emission in the orange-red region, with the strongest emission line at about 648 nm and possessing a good luminescence thermal stability between 78 and 500 K. With the increase in the Sm3+ content, the concentration quenching is observed due to the cross-relaxation (CR) processes among the Sm3+ ions. Upon 340 nm excitation, the Ce3+-doped phosphor presents a broad emission band in the blue region with a maximum at about 420 nm, which overlaps well with the 6H5/2 → 6P3/2 excitation line of Sm3+ and implies the possible energy transfer from Ce3+ to Sm3+. The spectral and decay measurements of the Ce3+ and Sm3+ co-doped samples are conducted and the Inokuti-Hirayama (I-H) model is adopted to analyze the luminescence decay dynamics of the donor Ce3+. Owing to the evident sensitization of the Sm3+ by the Ce3+ ions, the co-doped samples exhibit color variation under different wavelength excitations, endowing them with potential applications in optical anti-counterfeiting.