Methyl methacrylate-modified polystyrene microspheres: an effective strategy to enhance the fluorescence of Eu-complexes.

The in vitro detection applications of europium complex-doped microspheres mainly rely on strong fluorescence intensity and a well-defined morphology. In this work, using methyl methacrylate-modified polystyrene microspheres has been proven an effective strategy to enhance the fluorescence and morphology of Eu-complexes. The experimental results showed that the modification resulted in the formation of a porous structure within the polystyrene microspheres, enhancing the doping uniformity and facilitating a more significant accumulation of fluorescent molecules. Furthermore, because of their encapsulation ability, microspheres efficiently confine the fluorescent molecules within them. In addition, the nano-scale porous structure endowed the microspheres with enhanced properties without compromising solvent swelling capability, thereby significantly boosting the fluorescence performance of porous PSMMA. In lateral flow immunoassays (LFIAs), PSMMA-Eu microspheres were effectively utilized to detect fentanyl with exceptional sensitivity by capitalizing on these benefits, capable of detecting concentrations as low as 0.10 ng mL-1. This technology has significant potential for rapid point-of-care screening and clinical applications.

Rapid determination of serum amyloid A using an upconversion luminescent lateral flow immunochromatographic strip.

The early diagnosis and real-time prognosis of cardiovascular diseases (CVDs) at the bedside are important. However, real-time detection of myocardial infarction involves the use of large-scale instrumentation and long test times. Herein, a simple, rapid and sensitive lateral flow immunochromatographic strip (LFIS) based on Yb/Er co-doped NaYF4 upconversion nanoparticles (UCNPs) was demonstrated for use in the detection of myocardial infarction. First, through heavy Yb/Er doping and an inert NaYF4 shell coating on the nanoparticles, the surface-related luminescence quenching effect of UCNPs was eliminated to enhance the upconversion luminescence. Second, through uniform coating of a SiO2 layer on the UCNPs, the biological affinity was improved to couple UCNPs and antibody proteins. Finally, through modification and activation with a specific antibody protein (serum amyloid A (SAA)), the UCNPs exhibited intense upconversion luminescence and high specificity when applied as a lateral flow immunochromatographic strip (LFIS). The developed UC-LFIS was highly sensitive (0.1 µg mL-1) and specific for detecting SAA in only 10 µL of serum. The UC-LFIS holds great potential for the early diagnosis and prognosis of CVDs.

Ultrastable Laurionite Spontaneously Encapsulates Reduced-dimensional Lead Halide Perovskites.

Reduced dimensional lead halide perovskites (RDPs) have attracted great research interest in diverse optical and optoelectronic fields. However, their poor stability is one of the most challenging obstacles prohibiting them from practical applications. Here, we reveal that ultrastable laurionite-type Pb(OH)Br can spontaneously encapsulate the RDPs in their formation solution without introducing any additional chemicals, forming RDP@Pb(OH)Br core-shell microparticles. Interestingly, the number of the perovskite layers within the RDPs can be conveniently and precisely controlled by varying the amount of CsBr introduced into the reaction solution. A single RDP@Pb(OH)Br core-shell microparticle composed of RDP nanocrystals with different numbers of perovskite layers can be also prepared, showing different colors under different light excitations. More interestingly, barcoded RDP@Pb(OH)Br microparticles with different parts emitting different lights can also be prepared. The morphology of the emitting microstructures can be conveniently manipulated. The RDP@Pb(OH)Br microparticles demonstrate outstanding environmental, chemical, thermal, and optical stability, as well as strong resistance to anion exchange processes. This study not only deepens our understanding of the reaction processes in the extensively used saturation recrystallization method but also points out that it is highly possible to dramatically improve the performance of the optoelectronic devices through manipulating the spontaneous formation process of Pb(OH)Br.

Visible-NIR Photodetectors Based on Low-Dimensional GeSe Micro-Crystals: Designed Morphology and Improved Photoresponsivity.

GeSe micro-sheets and micro-belts have been synthesized by a facile one-pot wet chemical method in 1-octadecene solvent and oleic acid solvent, respectively. The adsorption of more oleic acid molecules on the (002) plane promoted growth along [010] direction of the GeSe micro-belts and limited carrier transport in this direction, resulting in higher carrier concentration and mobility of the GeSe micro-belts. The performance of the photodetectors based on the single GeSe micro-sheet and the single GeSe micro-belt was investigated under illumination at 532 nm, 980 nm and 1319 nm. Both, photodetectors based on a single GeSe micro-sheet and a single GeSe micro-belt, exhibit a high photoresponse, short response/recovery times, and long-term durability. Moreover, the photodetector based on a single GeSe micro-belt displays a broadband response with a high responsivity (5562 A/W at 532 nm, 1546 A/W at 980 nm) and detectivity (3.01×1012 Jones at 532 nm, 8.38×1011 Jones at 980 nm). These excellent characteristics render single GeSe micro-belts very interesting for use as highly efficient photodetectors, especially in the NIR region.

Temperature dependent molecular fluorescence of [Agm]n+ quantum clusters stabilized by phosphate glass networks.

Molecule like silver quantum clusters ([Agm]n+ QCs) exhibit an ultrasmall size confinement resulting in efficient broadband fluorescence. However, free [Agm]n+ QCs are also chemically active, so their stabilization is required for practical applications. We report in this work a phosphate oxyfluoride glass network enabled stabilization strategy of [Agm]n+ QCs. A series of silver-doped P2O5-ZnF2-xAg glasses were prepared by a conventional melt-and-quench method. The NMR and XPS results reveal that two types of [P(O,F)4] tetrahedrons (Q1, Q2) form chain structures and Zn(iv) connects [P(O,F)4] chains into a 3-dimension network in the glasses. The frameworks with limited void spaces were designed to restrict the polymerization degree, m, of [Agm]n+ QCs; the negatively charged tetrahedrons were designed to restrict the charge, n, of [Agm]n+ QCs. Through optical and mass spectroscopy studies, silver quantum clusters, [Ag2]2+ and [Ag4]2+, were identified to be charge compensated by [ZnO4] tetrahedrons and surrounded with [P(O,F)4] complex anions. The fluorescence thus gives high quantum efficiencies of 55.2% and 83.4%, for P2O5-ZnF2-xAg glass stabilized [Ag2]2+ and [Ag4]2+ QCs, respectively. This further reveals that the peak fixed fluorescence of [Ag2]2+ and [Ag4]2+ can be described by molecular fluorescence mechanisms. These are parity-allowed singlet-singlet transitions (S1 → S0), parity-forbidden triplet-singlet transitions (T1 → S0) and intersystem crossings between singlets (S1) and triplets (T1). The phonon coupled intersystem crossing between singlets (S1) and triplets (T1) determines the phosphate stabilized [Ag4]2+ QCs to exhibit a series of temperature dependent fluorescence behaviors. These include fluorescence intensity (at 50-200 K), intensity ratio (FIR) (at 50-200 K), peak shift (at 100-300 K) and lifetime (at 300-450 K) with maximum sensitivities of 1.27% K-1, 0.94% K-1, 0.29% K-1 and 0.41% K-1, respectively. Therefore, phosphate stabilized [Ag4]2+ QCs can be applied as temperature sensing probes, especially at low temperatures (10-300 K) and for color-based visualized temperature sensors.

High performance optical temperature sensing via selectively partitioning Cr4+ in the residual SiO2-rich phase of glass-ceramics.

Quadrivalent Cr4+ theoretically exhibits great potential to achieve higher photo-luminescence (PL) lifetime based temperature sensitivity than the commonly utilized trivalent Cr3+, but the problem is how to stabilize the anomalous quadrivalent chemical state of Cr4+. Here we propose a type of glass-ceramic phase structure with a precipitated ZnAl2O4 crystalline sub-phase and a residual ZnO-SrO-SiO2 glassy sub-phase, where Cr4+ can be well stabilized in the residual glassy sub-phase. From PL spectra, Cr4+ or Cr3+ was found to be located at Td (tetrahedral crystal filed) or Oh (octahedral crystal filed) sites with a relatively high crystal field strength. The thermally coupled 1E(1D)/3T2(3F) states of Cr4+ or the 2E(2G)/4T2(4F) states of Cr3+ were revealed as competitive energy level pairs suitable for PL lifetime based temperature sensing. Quadrivalent Cr4+ had a particular PL lifetime ratio of 1E(1D)/3T2(3F) up to 103, which was much higher than that (101) of trivalent Cr3+:2E(2G)/4T2(4F). This supported Cr4+ to eventually achieve a higher temperature sensitivity (1.72% K-1) one order of magnitude higher than that of Cr3+ (0.83% K-1). This provides the possibility of utilizing Cr4+-doped glass to develop a type of temperature sensor with high precision and sensitivity.

Thermal Enhancement of Upconversion by Negative Lattice Expansion in Orthorhombic Yb2 W3 O12.

Thermal quenching of photoluminescence represents a significant obstacle to practical applications such as lighting, display, and photovoltaics. Herein, a novel strategy is established to enhance upconversion luminescence at elevated temperatures based on the use of negative thermal expansion host materials. Lanthanide-doped orthorhombic Yb2 W3 O12 crystals are synthesized and characterized by in situ X-ray diffraction and photoluminescence spectroscopy. The thermally induced contraction and distortion of the host lattice is demonstrated to enhance the collection of excitation energy by activator ions. When the temperature is increased from 303 to 573 K, a 29-fold enhancement of green upconversion luminescence in Er3+ activators is achieved. Moreover, the temperature dependence of the upconversion luminescence is reversible. The thermally enhanced upconversion is developed as a sensitive ratiometric thermometer by referring to a thermally quenched upconversion.

Phase separation strategy to facilely form fluorescent [Ag2]2+/[Agm]n+ quantum clusters in boro-alumino-silicate multiphase glasses.

By adjusting the content of ZnF2-SrF2/ZnO-SrO, a series of SiO2-Al2O3-B2O3-Na2O-ZnO/ZnF2-SrO/SrF2-Ag multiphase glasses was designed and prepared via a melt-quenching method. Under a phase separation strategy, negatively charged tetrahedrons ([BO4]-, [ZnO4]2-, and [AlO4]-) can be generated to stabilize different silver species (Ag+ ions; [Ag2]2+ pairs; [Agm]n+ quantum clusters ([Agm]n+ QCs)) in B2O3-rich and ZnO-Al2O3 rich sub-phases. The B2O3-rich sub-phase has a high solubility for Ag+ ions and [Agm]n+ QCs. The fluoride-rich phase shows a good ability to extract Na+ from the B2O3-rich sub-phase, significantly affects the solubility of Ag+ in the B2O3-rich sub-phase, and eventually determines the aggregation from Ag+ ions and Ag0 atom to [Agm]n+ QCs. The ZnO-Al2O3-rich or ZnO-SiO2-rich (i.e. SiO2-rich in GZnOSrO) phase has a relatively high solubility for [Ag2]2+ pairs. The Ag+/[Ag2]2+/[Agm]n+ QC fluorescent centers were identified by spectroscopic analysis, where the fluorescence bands are located in the ultraviolet, green-white and orange spectral regions, respectively. The fluorescent quantum yield (QY) of the [Agm]n+ QCs can be improved to 55.7%, and the combination of these three luminescent centers can achieve white light emission.

Facile Synthesis of γ-In2 Se3 Nanoflowers toward High Performance Self-Powered Broadband γ-In2 Se3 /Si Heterojunction Photodiode.

An effective colloidal process involving the hot-injection method is developed to synthesize uniform nanoflowers consisting of 2D γ-In2 Se3 nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In2 Se3 , a high-quality γ-In2 Se3 /Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long-term durability. In addition, the γ-In2 Se3 /Si heterojunction photodiode is self-powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ-In2 Se3 /Si heterojunction very interesting as highly efficient photodetectors.

Stabilization of ultra-small [Ag2]2+ and [Agm]n+ nano-clusters through negatively charged tetrahedrons in oxyfluoride glass networks: To largely enhance the luminescence quantum yields.

Herein, three different silver species were stably formed in SiO2-Al2O3-B2O3-Na2O-ZnF2-CaF2 glasses and were identified by their characteristic luminescence bands: violet blue luminescence (Ag+: 4d95s1 → 4d10), green white molecular fluorescence (molecule-like [Agm]n+, named ML-Ag) and orange molecular fluorescence ([Ag2]2+ pairs). Due to the relatively low aggregation degrees of [Agm]n+ and [Ag2]2+, non-radiative transitions were highly suppressed, and the PL quantum yields (QYs) of ML-Ag and [Ag2]2+ pairs reached 73.7% and 89.7%, respectively. The substitution of 0.5B2O3-0.5Na2O with SiO2 promoted the partial reduction of Ag+ to Ag0 and the subsequent aggregation of Ag+ and Ag0 to form [Agm]n+ (ML-Ag). The absence of Na2O also resulted in an increasing amount of Ag+-Ag+ pairs with closing interionic distance to form [Ag2]2+ in glass. According to the X-ray photoelectron spectra (XPS) and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra, a solubility strategy and a charge compensation model were proposed to describe the transformations between different silver species. The formation of ML-Ag was further controlled via the solubility of Ag+ in glass, whereas [Ag2]2+ centers could be effectively produced by lowering the total amount of other competitive charge compensators, such as Na+, or by introducing negatively charged [BO4]-, [AlO4]-, and [ZnO4]2- tetrahedrons into the glass matrix.