Luminescence Enhancement Research Articles

Photophysical Properties and DNA Binding of Two Intercalating Osmium Polypyridyl Complexes Showing Light-Switch Effects.

The synthesis and photophysical characterization of two osmium(II) polypyridyl complexes, [Os(TAP)2dppz]2+ (1) and [Os(TAP)2dppp2]2+ (2) containing dppz (dipyrido[3,2-a:2′,3′-c]phenazine) and dppp2 (pyrido[2′,3′:5,6]pyrazino[2,3-f][1,10]phenanthroline) intercalating ligands and TAP (1,4,5,8-tetraazaphenanthrene) ancillary ligands, are reported. The complexes exhibit complex electrochemistry with five distinct reductive redox couples, the first of which is assigned to a TAP-based process. The complexes emit in the near-IR (1 at 761 nm and 2 at 740 nm) with lifetimes of >35 ns with a low quantum yield of luminescence in aqueous solution (∼0.25%). The Δ and Λ enantiomers of 1 and 2 are found to bind to natural DNA and with AT and GC oligodeoxynucleotides with high affinities. In the presence of natural DNA, the visible absorption spectra are found to display significant hypochromic shifts, which is strongly evident for the ligand-centered π–π* dppp2 transition at 355 nm, which undergoes 46% hypochromism. The emission of both complexes increases upon DNA binding, which is observed to be sensitive to the Δ or Λ enantiomer and the DNA composition. A striking result is the sensitivity of Λ-2 to the presence of AT DNA, where a 6-fold enhancement of luminescence is observed and reflects the nature of the binding for the enantiomer and the protection from solution. Thermal denaturation studies show that both complexes are found to stabilize natural DNA. Finally, cellular studies show that the complexes are internalized by cultured mammalian cells and localize in the nucleus.

An electrochemiluminescence biosensor based on Graphitic carbon nitride luminescence quenching for detection of AFB1

Based on graphite-like carbon nitride (g-CN) nanocomposites coupled with aptamer, a regenerable electrochemiluminescence (ECL) biosensor is developed for the quantitative detection of aflatoxin B1 (AFB1). In the existence of AFB1, the structure of the aptamer changed into a loop, and the original ECL intensity was reduced owing to the enhancement of luminescence quenching between the ferrocene modified at the end of the aptamer and the luminescent substrate g-CN. Moreover, AFB1 with oxidation state could also react with high energy state g-CN, leading to further reduction of the electrochemiluminescence signal. At optimum conditions, ECL intensity was decreased in linearity with an AFB1 concentration range from 0.005 ng/mL to 10 ng/mL, and the minimum detectable concentration was down to 0.005 ng/mL, which realized trace detection demand with high sensitivity. It was selective for AFB1 and its performance had been verified on rice samples, which indicated a promising applying prospect of non-enzymatic electrochemiluminescence AFB1 detection.

Synthesis of Orange-Red Emissive Au-SG and AuAg-SG Nanoclusters and Their Turn-OFF vs. Turn-ON Metal Ion Sensing.

Synthesis of luminescent metal cluster for selective sensing of specific analyte with detail mechanistic understanding is very important for real world applications as well as for developing new emissive materials. In the present work, we have synthesized L-glutathione stabilized gold (Au-SG) and gold-silver bimetallic (AuAg-SG) clusters under identical experimental conditions with orange red emissive characteristics for both. Detail photo physical analysis reveals that both clusters are phosphorescent in nature with moderate quantum yield of 7% and 19% for Au-SG and AuAg-SG respectively and their excited state lifetime values are in the range of 1-2μs. While Au-SG cluster showed luminescence quenching response (turn-off) in presence of Fe3+ and Hg2+ ions, AuAg-SG cluster showed turn-off response for Cu2+, Fe3+ and Hg2+, but luminescent enhancement (turn-on) response for Cd2+ ions. The highest detection limit obtained for Cu2+ ion by AuAg-SG cluster is 20nM while for Cd2+ ion it is 75nM. From Time Correlated Single Photo Counting (TCSPC) and Dynamic Light Scattering (DLS) measurements we postulated that except Cd2+, all other metal ions cause aggregation of clusters through ligation with SG ligands while Cd2+ ion does not induce any cluster aggregation but binds to cluster surface atoms. The near constant life time values of both clusters during gradual addition of respective metal ions confirms static quenching/enhancement process through formation of stable ground state adducts.

Terbium and barium codoped mesoporous silica nanoparticles with enhanced optical properties

• Mesoporous silica nanoparticles codoped with terbium and barium were synthesized. • Barium codoping significantly improved the quantum yield of SiO 2 -Tb nanoparticles. • Several luminescence enhancement mechanisms were proposed. In this study, we showed for the first time that barium (Ba) codoping improves the luminescent properties of terbium (Tb)-doped SiO 2 nanoparticles (NPs). In particular, the quantum yield (QY) of SiO 2 -Ba,Tb NPs was found to be ∼10.7%, whereas the QY of bare SiO 2 -Tb NPs was only ∼4.3%. Several mechanisms for luminescence enhancement have been proposed. We strongly believe that this methodology can be used to create alternative silica-based NPs with improved optical characteristics.

Designing and temperature sensing characteristics of upconversion luminescence core-shell structures with negative and positive thermal expansion

Generally, lanthanum ions doped positive expansion and negative expansion materials exhibit thermal quenching and enhancement of upconversion luminescence (UCL), respectively. Combining the UCL characteristics of positive expansion and negative expansion lattices is of importance for developing efficient temperature sensing systems. Here, positive expansion TiO 2 :Yb 3+ , Er 3+ three dimensionally ordered macroporous film was prepared by the template-assisted approach, and the Yb 2 W 3 O 12 : Er 3+ solution was filled into the TiO 2 : Yb 3+ , Er 3+ three dimensionally ordered macroporous film. After secondary sintering, the shell of negative expansion Yb 2 W 3 O 12 : Er 3+ was formed on the surface of TiO 2 :Yb 3+ /Er 3+ core. Under 980 nm excitation, the red and green UCL is predominate for the spectra of TiO 2 :Yb 3+ /Er 3+ core and Yb 2 W 3 O 12 : Er 3+ shell, respectively. With the measurement temperature increasing, the green UCL from negative expansion Yb 2 W 3 O 12 : Er 3+ shell increases, while the red UCL from positive expansion TiO 2 :Yb 3+ , Er 3+ core decreases. The performance of temperature sensing was characterized by the monitoring the UCL intensity ratio between 525 nm and 660 nm. The temperature sensitivity is about 1.12% K −1 , which is larger than that of thermally coupled FIR technology. We believed that the present work is instructive for developing new generation temperature sensor.

Lanthanoid hydrogen-bonded organic frameworks: Enhancement of luminescence by the coordination-promoted antenna effect and applications in heavy-metal ion sensing and sterilization

Enhancing the antenna effect to increase energy transfer to lanthanoid ions for generating bright luminescence is an effective strategy to construct lanthanoid luminophores with excellent performance. However, the antenna effect often depends on the structure, connection, and configuration of immobilized ligands. We found for the first time that the introduction of the Zn(II) ion coordination can greatly enhance the solid-state fluorescence and phosphorescence emission of lanthanoid hydrogen-bonded organic frameworks (Ln-HOFs). Notably, relative to that of Tb-HOF, the solid-state fluorescence intensity, quantum yield, and lifetime of TbZn-HOFs had increased by 17.09, 38.81, and 12.96 times, respectively. The chelating coordination of the Zn(II) ions effectively hindered the vibration of organic ligands to weaken nonradiative transitions and stabilized and reduced the triplet excited state of the ligands through the spin–orbit coupling effect, which led to the increased efficiency of energy transfer with Tb(III) ions. In aqueous solution, LnZn-HOFs released Ln(III) ions effectively and captured low concentrations of the heavy metal ion Cu(II), and the efficient ligand-to-Cu(II) ion energy transfer quenched ligand luminescence. Notably, the limit of detection (LOD) was calculated to be 1.91 nM, which was considerably lower than the maximum level of Cu(II) ions in drinking water (20 μM) specified by the United States Environmental Protection Agency and was better than the LOD of other previously reported probes. Furthermore, LnZn-HOFs can effectively inhibit the proliferation of classical Gram-positive bacteria, such as Bacillus subtilis and Staphylococcus aureus, via ion release and thus showed a high sterilization effect. This work is the first to find that HOFs can exert efficient bacteriostatic and sterilization effects through ion release.

The enhancement of exciton-like luminescence in KCl single crystals under local and uniaxial elastic lattice deformation

Radiative annihilation of exciton-like formations (bound excitons) in KCl single crystals doped with various impurity cations (Li, Na, Sr) has been studied using highly sensitive luminescence methods. In KCl:Na with different sodium concentration, X-ray luminescence bands with the maxima at 2.8 and 3.1 eV, which and attributed to exciton-like formations in the region of local lattice deformation by single Na+ and pair Na+-Na+ centers, become significantly more intense with sodium impurity concentration. The luminescence efficiency of such bound anion excitons also increases in the KCl:Na crystals exposed to a uniaxial elastic stress along the 〈100〉 and 〈110〉 crystallographic directions. The influence of temperature as well as lattice symmetry lowering due to applied elastic deformation (external action) or local deformation in the vicinity of impurity ions (internal action) on the efficiency of the recombination formation of bound excitons has been analyzed.

Luminescence Enhancement of a Gold Nanocluster Hydrogel Facilitated by Water for Erasable Water Writing and Visual Solvent Differentiation

Luminescence Enhancement of a Gold Nanocluster Hydrogel Facilitated by Water for Erasable Water Writing and Visual Solvent Differentiation

Synthesis and luminescence enhancement of red-emitting [formula omitted] phosphors via [formula omitted] Co-doping prepared by microwave solution combustion synthesis

A series of Ca3Y(AlO)3(BO3)4:Eu3+,La3+ red phosphors have been successfully synthesized via a mixed-fuel microwave solution combustion synthesis. In this study, the structural, morphological and optical properties of the phosphors as a function of annealing temperature and time were systematically investigated. The X-ray diffraction analysis confirmed the formation of the hexagonal Ca3Y(AlO)3(BO3)4 structure at 900 °C and the powder crystallinity depends critically on the annealing condition. The diffuse reflectance and excitation spectra revealed that the phosphor exhibits a strong absorption in the near-ultraviolet region (396 nm) that matched well with NUV LEDs. Under 396 nm excitation, the Ca3Y(AlO)3(BO3)4:Eu3+ emits intense orange-red emissions, and the optimal fluorescence intensity was attained after annealing at 1000 °C for 5 h. Meanwhile, an appropriate amount of La3+ co-doping significantly enhanced the luminescence of Ca3Y(AlO)3(BO3)4:Eu3+, which were due to the environment distortion of the crystal field induced by the difference in ionic radius. The electroluminescence measurement confirmed that the Ca3Y(AlO)3(BO3)4:Eu3+,La3+ phosphor could be efficiently excited by commercial NUV LED chips. These results indicated that the synthesized Ca3Y(AlO)3(BO3)4:Eu3+,La3+ phosphor could serve as a potential red-emitting component for NUV based-white LEDs.

Upconversion luminescence enhancement of the ytterbium oxide with gold nanoparticles on anodized titanium surface

This paper presents a study of the cooperative luminescence (upconversion) process of Yb2O3 with gold nanoparticles on the anodized titanium surface. The luminescence of the samples was registered under two-photon excitation with using infrared laser (λ = 980 nm) and a quasi-continuous femtosecond laser (λ = 1030 nm). It was found that the quantum yield of luminescence in the presence of gold nanoparticles increases in 5.6 times fold as a result of non-radiative plasmon energy transfer. The constant of non-radiative dipole-dipole energy transfer was calculated with using the Förster model under the plasmon energy generation. It is also shown that under photoexcitation with wavelength of 980 nm at low temperatures (80 K), the intensity of upconversion luminescence increases according to the quadratic function of the excitation energy, which confirms the existence of upconversion luminescence generation by the mechanism of simultaneous energy transfer involving two Yb3+ ions in the oxide crystal.

Improved the stability and enhanced luminescence of Er doped CsPbBr3 perovskite

Cesium lead bromide (CsPbBr3) perovskite has gained significance owing to its potential performance in optoelectronic devices. Here, using the first-principles calculations based on density functional theory, we investigate the effect of Er substitution on Pb atom position on the structural, electronic, and optical properties of CsPbBr3 for improving its luminescence properties. We show that the doping system with highest doping concentration yields the lowest negative binding energy, suggesting that Er doping can enhance the stability of CsPbBr3 well. The calculated band structures indicate that the CsPb1-xErxBr3 system is a p-type semiconductor with the direct bandgap, and the bandgap increases with the increase of Er doping concentration. Interestingly, the Er defect levels obviously appear in bandgap, effectively decreasing the difficulty of the electronic transition. The density of states also show that there are more Er 4f→4f and less Er 4f→Er 5d electronic transition exiting in CsPb1-xErxBr3 system, which are the main origins of luminescence enhancement for CsPbBr3. Furthermore, the optical properties are also analyzed and they imply that the Er doping can improve the optical properties of CsPbBr3 in infrared phonon energy region, and nearly retain the optical properties of CsPbBr3 in other phonon energy region. Our work provides a new luminescence tunable design strategy for Er-doped perovskite materials for the optical communication application.

Augmentation of photophysical features and Judd-Ofelt analysis of extensively green glowing terbium (III) complexes with nitrogen donor ancillary ligands.

Six green glowing terbium (III) complexes were fabricated via grinding method utilizing a prime organic ligand (L) and nitrogen donor ancillary ligands. Characterization of synthesized complexes was accomplished through various spectroscopic techniques. The significant thermal stability was determined by thermogravimetric analysis while the energy bandgap and Urbach energy were investigated through diffused reflectance spectra of these complexes. The peak observed at 548nm in emission spectra is responsible for the virescent color of these complexes. Color purity, decay time, quantum yield, and emission intensities of ternary complexes were significantly improved as compared to binary ones due to the synergistic effect of ancillary ligands. Judd-Ofelt parameters were determined by the NIR absorption spectrum, which claims the asymmetric environment around the terbium (III) ion. CCT values advocate the applicability of these complexes in green light-emitting materials as a cool light source. The biological assignments reveal the significance of these complexes as potent antioxidants and antimicrobial agents. The energy transfer process highlights the enhancement of luminescence in these complexes via the synergic effect of ligands. Our investigation portrays that these complexes can be employed in laser technology, display devices, semiconductors, biological fields, and optoelectronic devices.

Achieving and Understanding of Highly Efficient Ternary Organic Photovoltaics: From Morphology and Energy Loss to Working Mechanism.

Ternary strategy, adding an additional donor (D) or acceptor (A) into conventional binary D:A blend, has shown great potential in improving photovoltaic performances of organic photovoltaics (OPVs) for practical applications. Herein, this review is presented on how efficient ternary OPVs are realized from the aspects of morphology, energy loss, and working mechanism. As to morphology, the role of third component on the formation of preferred alloy-like-phase and vertical-phase, which are driven by the miscibility tuning, is discussed. For energy loss, the effect of the third component on the luminescence enhancement and energetic disordering suppression, which lead to favorable increase of voltage, is presented. Regarding working mechanism, dilution effect and relationships between two acceptors or donor/acceptor, which explain the observed device parameters variations, are analyzed. Finally, some future directions concerning ternary OPVs are pointed out. Therefore, this review can provide a comprehensive understanding of working principles and effective routes for high-efficiency ternary systems, advancing the commercialization of OPVs.

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

We investigated the photon emission spectra on Ag (111) surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum. Characteristic plasmon modes were illustrated as a function of the bias voltage. The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current. Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages, as well as at the field emission resonance with bias voltage increased up to 9 V. Presence of a silver (Ag) nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances, which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum. The results are of potential value for applications where ultimate enhancement of photon emission is desired.

Structural and optical characterization of tungsten phosphate glasses containing silver and erbium

Tungsten-phosphate glasses with up to 20 mol% of silver chloride content were prepared using the conventional melt-quenching method. Ag nanoparticles (AgNPs) formation was achieved by nucleation and growth using controlled thermal treatment. Thermal properties and the local structure were studied as a function of Ag content by means of DSC, Raman and 31P MAS NMR spectroscopy. The Ag NP growth was monitored by real-time UV–Vis spectroscopy and confirmed by TEM. The optical linear and nonlinear properties were evaluated as a function of the AgNPs growth. NIR emission of Er3+ ions was studied and showed a strong dependence on the AgNPs size. A weak luminescent enhancement occurs when small AgNPs are present, but on the other hand, a strong quenching takes place in the presence of larger AgNPs, due to the local field effect mediated by surface plasmon resonance (SPR) and Er3+ intersystem crossing processes, respectively. A stronger luminescence suppression by excitation at 545 nm was assigned to the increased contribution to back-energy transfer from Er3+ to AgNPs and re-absorption by SPR. These results highlight the importance of a careful study of the relation between noble metal NPs size and the excitation wavelength to increase the efficiency of the future photonic devices, such as NIR solid state laser, Kerr effect-based laser or amplifiers.

Regulative control and enhancement of multi-color upconversion luminescence with DBR cavities

Upconversion luminescence (UCL) of lanthanide-doped materials (e.g. NaYF4:Yb3+/Er3+) involves multi-step, multi-channel transitions (corresponding to multi-color emissions) in a multi-level system, and is a low-efficiency nonlinear process. Usually, the UCL is enhanced by local enhancement of the excited field or one of its multi-color emissions is promoted by matching with a resonance cavity mode based on Purcell effect. Here, we propose to regulatively control and enhance the UCL by fostering one color of the UCL emissions with a resonance mode and inhibiting the other with an anti-resonance or nonresonance mode in forbidden band in an optical cavity, so that excited-state ions (e.g. Er3+) transit to the ground state more via the fostered UCL emission channel, rather than the inhibited one. As such, high-contrast single-color UCL emission can be achieved with an enhancement beyond that of Purcell effect. For the purpose, superior mode properties of distributed Bragg reflector (DBR) cavities can be applied, whose forbidden band of the DBR layers and resonance cavity mode in the forbidden band can be independently tuned in positions to match with the UCL emissions for them to be inhibited and fostered respectively. In experimental implementation, multi-color UCL (e.g. red and green) of NaYF4:Yb3+/Er3+ nanoparticles embedded in such DBR cavities are studied. And high-contrast single-color UCL emissions are demonstrated with enhancements factors beyond Purcell factors calculated in numerical simulations. A hypothesis on modifications of intermediate transitions in the UCL processes, as feedbacks to influences of mode characteristics in the DBR cavities for regulative control, is also proposed to explain the phenomena. The work suggests a way to regulatively control multi-channel photon emissions in multi-level systems for enhanced single-channel photon emission.

Surface crystallization enhanced upconversion luminescence in NaGdF4:Yb,Er@NaYF4 core/shell nanocrystals

Coating upconversion nanocrystals with an inert shell for removing surface defects is confirmed to be an efficient way for remarkably enhancing upconversion luminescence. However, it is not clear whether surface atomic structures on the outer inert shell affect upconversion luminescence of active cores. Here, we improved the surface crystallinity of NaGdF4:Yb,Er@NaYF4 active-core/inert-shell nanocrystals using ultrasonic oscillation. It was observed that surface crystallization of the inert shell could lead to an obvious enhancement in upconversion luminescence. The improved surface crystallinity has no obvious influence on the electronic transition in upconversion luminescence processes, but decrease the scattering and absorption to excitation and emission photons. This result clearly indicates that surface crystallization of the inert shell is a powerful route for further enhancing upconversion luminescence besides of the concept of core/shell structure.

Rare‐earth composite as optical upconversion temperature sensor

In this work, rare-earth composite as an optical upconversion temperature dual mode sensing is practically demonstrated. NaGdF4:Yb3+/Er3+/Zn2+ phosphor was synthesized by the solvothermal method. The phase purity, crystal structure and morphologies were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The enhancement of upconversion luminescence is achieved by aliovalent doping in Zn2+ co-doped NaGdF4: Yb3+/Er3+ phosphors. The temperature sensing behaviours based on the luminescence intensity and luminescence lifetime in phosphors are recorded in the temperature range from 75 to 297 K, and the maximum sensitivity is obtained as 13.4 × 10−3 K−1 at 75 K and 2.52 × 10−3 K−1 at 225 K, respectively.

Thermal Enhancement of Luminescence for Negative Thermal Expansion in Molecular Materials.

Overcoming thermal quenching is an essential issue in the practical application of luminescent materials. Herein, we found that negative thermal expansion (NTE) can achieve the thermal enhancement of luminescence in molecular materials based on three metal-organic frameworks CuX-bpy (X = Cl, Br, I; bpy = 4,4'-bipyridine). All complexes exhibit NTE on the c-axis, and the strongest NTE leads to a contraction of the Cu...Cu distance in CuCl-bpy, which further intensifies the luminescence emission. This phenomenon indicates the existence of thermally enhanced charge transfer. Moreover, the origin of the distinction in charge transfer attributed to the different valence states of the copper is investigated through the combined studies of X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory calculations. This research provides a new approach to modulating the luminescence thermal enhancement by NTE.

Development of a NIR iridium(III) complex for self-calibrated and luminogenic detection of boron trifluoride

Boron trifluoride (BF3) is a potential environmental pollutant, and excess exposure to it may cause human diseases. However, the sensitive, rapid and accurate detection of BF3 for on-site purposes is still a challenge. In this work, we developed the first NIR iridium(III)-based probe with dual emission and a Stokes shift of 370 nm for self-calibrated and luminogenic detection of BF3. This probe exhibited a strong luminescence enhancement at around 650 nm to BF3 (0–100 μM) with almost no change in luminescence at 475 nm, displaying a 220-fold I650 nm/I475 nm enhancement at 100 μM of BF3 with a detection limit of 0.35 μM. Moreover, the probe showed a fast response time of less than 5 s to BF3 along with an obvious color change under UV irradiation for visual detection. Importantly, the desirable photophysical properties of the iridium(III)-based probe can be harnessed for time-resolved detection of BF3 in the presence of the fluorescence background. The applicability of the probe was further verified in an organic solvent waste-spiked system and on a glass pane. This work will provide a solid basis for the development of sensitive and on-site BF3 sensing toolkits for environmental monitoring.