Luminescence Enhancement Research Articles

Nanoporous AlGaN-based distributed Bragg reflectors with enhanced luminescence for wafer-scale ultraviolet light-emitting devices

The large-area (20.3 cm2) NP-AlGaN DBRs, which are prepared via electrochemical (EC) etching in an acid solution, present high reflectivity (>90%) and wide spectral stopband. Then the nanoporous AlGaN Distributed Bragg reflectors (NP-AlGaN DBRs) are used as substrates for regrowth of ultraviolet light-emitting diodes (LEDs). Compared to those of the reference LEDs, the ultraviolet LEDs with the DBRs show sixfold enhancement and red-shift of the luminescence peak, as well as a rising PL lifetime. Luminescence enhancement is owing to the low defect density of the AlGaN/GaN MQWs and high light reflection effect of the NP-AlGaN DBRs. The red-shift is due to the stress relaxation in the AlGaN/GaN MQWs layer related to the wet etching and regrowth process.

Porous Supramolecular Assembly of Pentiptycene-Containing Gold(I) Complexes: Persistent Excited-State Aurophilicity and Inclusion-Induced Emission Enhancement.

We report herein a porous supramolecular framework formed by a linear mononuclear Au(I) complex (1) via the tongue-and-groove-like joinery between the pentiptycene U-cavities (grooves) and the rod-shaped π-conjugated backbone and alkyl chains (tongues) with the assistance of C-H···π and aurophilic interactions. The framework contains distorted tetrahedral Au4 units, which undergo stepwise and persistent photoinduced Au(I)-Au(I) bond shortening (excited-state aurophilicity), leading to multicolored luminescence photochromism. The one-dimensional pore channels could accommodate different solvates and guests, and the guest inclusion-induced luminescence enhancement (up to 300%) and/or vapochromism are characterized. A correlation between the aurophilic bonding and the luminescence activity is uncovered by TDDFT calculations. Isostructural derivatives 2 and 3 corroborate both the robustness of the porous supramolecular assembly and the mechanisms of the stimulation-induced luminescence properties of 1. This work demonstrates the cooperation of aurophilicity and structural porosity and adaptability in achieving novel supramolecular photochemical properties.

Luminescence enhancement and tunable color emission in Eu/Dy/Sm codoped CaW1- xMoxO4 phosphor

• A series of Eu 3+ activated CaMoxW1-xO4 phosphors were prepared. • The influence of [MoO 4 ] addition on the vibrational pattern, band gap and luminescence emission was studied. • The energy transfer from [WO 4 ] to Eu 3+ through the [MoO4] as sensitizer was discussed. • The enhancement of color tunability was reported in this paper. A series of Eu 3+ - activated CaW 1-x Mo x O 4 phosphors possessing schellite type crystalline structure were synthesized by using hydrothermal method to study the influence of molybdate doping on the luminescent performances of CaWO 4 :Eu 3+ phosphors. The phase composition, vibrational spectra and luminescent properties were characterized by X-ray diffraction, fourier transform infrared, and photoluminescence spectroscopy. The addition of [MoO 4 ] does not affect the crystalline phases of the synthesized materials. The effect of addition of [MoO 4 ] into the (Ca,Eu)WO 4 on the band gap of the phosphor and Eu 3+ emission has been studied. The strongest emission at 618 nm is corresponding to 5 D 0 → 7 F 2 transition of Eu 3+ under 273 nm excitation indicating that the site symmetry of the Eu 3+ ions was not affected. A red shift in the excitation spectra of the [WO 4 ] was observed with increasing [MoO 4 ] content. Further, color-tunable emissions were also studied by the co-doping of Dy 3+ and Sm 3+ into the (Ca,Eu)W 0.80 Mo 0.20 O 4 phosphor indicating the potential candidate for light emitting diodes.

Rapid and Specific Enhanced Luminescent Switch of Aniline Gas by MOFs Assembled from a Planar Binuclear Cadmium(II) Metalloligand.

Due to the low vapor pressure of aniline, it is challenging to develop a specific rapid fluorescence detection material for low concentrations of aniline gas, which is suspected to result in carcinogenicity when people are exposed by ingestion, inhalation, and skin contact. Herein, the easy-preparing Schiff base ligands were employed to construct the binuclear cadmium(II) compounds featuring a good plane and fine luminescent property, and then, the end groups were changed, making the compounds metalloligands to further build the 3D metal-organic frameworks (MOFs), named MECS-2. It is found that MECS-2 can achieve specific luminescent enhancement response for aniline gas. Furthermore, a large-scale MECS-2a film could be easily prepared by electrospinning nanoMECS-2, which presents the highly efficient and visual detection for aniline gas with the luminescent enhancement effect up to 20 times and good repeatability. Our work provides a good example for the efficient construction of MOF-based films with the fluorescence detection function for organic aromatic gases.

SPR coupled luminescence enhancement of Er3+/Au NPs -doped multicomponent tellurite glasses

Glasses of the composition (59.6-x)TeO2+10K2O+10P2O5+10B2O3 +10ZnF2+0.4Er2O3+xAu2O3 (x = 0.1, 0.2, 0.3 and 0.4 mol%) were produced by means of melt-quenching method and thoroughly analyzed using EDS, XRD, TEM, DSC, UV–Visible–NIR absorption and photoluminescence (PL) techniques. These Au incorporated glasses were investigated for their surface plasmonic resonance (SPR) coupled luminescence enhancement. The plasmonic absorptions of gold have been evidenced through the presence of absorption bands at 599 nm and 652 nm. Direct and indirect optical band gap and the urbach energies were estimated from the absorption spectra. Well dispersed nanoparticles having an average size of 10 nm was verified by TEM analysis. Plasmonic coupled enhancement in the characteristic emission of Er3+ ions and in other spectral parameters were traced and quantified. The visible as well as NIR emission spectra, Judd-Ofelt spectroscopic parameters and other critical spectroscopic properties were computed, which were further characterized via CIE diagram to analyse the suitability of the prepared glasses for optical applications. The studies revealed that the prepared glasses impart enormous scope in the field of solid-state lasers and color display devices.

Enhanced infrared luminescence of multifunctional-nanoparticle-composited transparent solids

Amorphous transparent solid glass doped with functional nanoparticles may have considerable potential in military and civilian fields, for the exploration of highly efficient laser materials. Secondary melting technology and spontaneous precipitation of precious metals were employed to prepare dual-phase nanocrystalline glass ceramics containing Ag nanoparticles and Gd2O3:Er, and the prepared ceramics exhibited high optical transmittance. The microscopic morphologies and possible structural changes of the embedded nanoparticles were confirmed by using Raman spectroscopy and transmission electron microscopy. Based on the results of the fluorescence spectra and lifetime, the source and possible causes of luminescence enhancement were explained. The crystal environment of Gd2O3 and the characteristics of Ag nanoparticles resulted in a substantial increase in infrared emission, indicating that this composite is expected to be a potentially efficient laser gain material.

Role of Na+ co-doping in luminescence enhancement of Bi2O3: Sm3+ nanophosphors

In this paper, we present a comprehensive structural and optical study of alkali metal ion (Na+) co-doping in samarium-doped bismuth oxide nanophosphors and its role in enhancing the red emission of the phosphors. X-ray diffraction (XRD) analysis ascertains the monoclinic crystal structure (space group P21/c) of the synthesized phosphors with crystallite size in the 49–65 nm range. The XRD analysis also reveals an improvement in crystallinity after Na+ co-doping in Sm3+ doped Bi2O3 phosphors. The HR-SEM micrographs reveal the nanosheet-like morphology and the EDX spectroscopy confirms the presence of all elements in the prepared phosphors. The TEM analysis validates the structural and morphological findings. The UV–Vis–NIR spectroscopic analysis has been carried out to estimate the bandgap as well as to investigate the Urbach energy of the phosphors. An augmentation in bandgap energy (2.784–2.807 eV) is observed for lower Na+ co-doping in samarium doped phosphor and shows a decreasing trend with increasing Na+ concentration. FTIR spectroscopy was probed to analyze the chemical bonding, modes of vibration, and detection of functional groups in the samples. The room temperature photoluminescence (PL) emission studies were performed under 481 nm excitation which exhibits an explicit redshift of the CIE coordinates. Nearly ten-fold enhancement in the emission intensity was observed in the optimized Bi2O3:(5%)Sm3+ with co-doping of 1% Na + ions. The lifetime of the 4G5/2 level of the Sm3+ ions has also increased on doping 1% Na+ ions. The thermal stability of the phosphors has been investigated using temperature-dependent PL analysis over the temperature range of 303–453 K. The correlated color temperature (CCT) analysis of the samples reveals that the prepared nanophosphors are promising and potential red-emitting phosphors to realize efficient optoelectronic and display devices.

Upconversion luminescence based inverted microfluidic chip for in situ CTCs capture, monitor and killing

Real-time counting of circulating tumor cells (CTCs) can effectively reduce false-negative results, which, however, is a major stumbling block in the practical CTCs capture process. In this paper, upconversion luminescence is introduced into the inverted microfluidic chip to realize real-time ratiometric luminescence CTCs detection by utilizing its advantage of near-infrared light. In view of the low upconversion luminescence efficiency, a double-layer YVO4 inverse opal photonic crystal (IOPC) structure has been designed, which not only serves as a capture surface for CTCs via bionic macroporous structure but also uses its double bandgap effect to implement spontaneous emission adjustment, obtaining 32 times enhancement of upconversion luminescence. Combined with anti-EpCAM-Fe3O4@Ce6@Silane probes and the inverted microfluidic design, a capture efficiency of more than 95% was achieved. When CTCs were captured, the red light of Ce6 molecules in the CTCs targeting nano-probes and the enhanced upconversion luminescence were used for real-time and ratiometric CTCs monitoring. Moreover, Ce6 molecules in the nanoprobes perform the function of photodynamic effect under red light irradiation, leading to the in-situ killing of CTCs inside the channel, which is a very practical and meaningful exploration in the process of preventing tumor metastasis.

Nanoparticle core size and spacer coating thickness-dependence on metal-enhanced luminescence in optical oxygen sensors

Metal-enhanced luminescence (MEL) originated from near field interactions of luminescence with the surface plasmon resonance (SPR) of nearby metallic nanoparticles (NPs) is an effective strategy to increase luminescence detection sensitivity in oxygen sensors. Once the excitation light induces SPR, the generated enhanced local electromagnetic filed will result in an enhanced excitation efficiency and an increased radiative decay rates of luminescence in close proximity. Meanwhile, the nonradioactive energy transfer from the dyes to the metal NPs, leading to emission quenching, can also be affected by their separation. The extent of the intensity enhancement depends critically on the particle size, shape and the separation distance between the dye and the metal surface. Here, we prepared core-shell Ag@SiO2 with different core sizes (35 nm, 58 nm and 95 nm) and shell thickness (5–25 nm) to investigate the size and separation dependence on the emission enhancement in oxygen sensors at 0–21% oxygen concentration. Intensity enhancement factors of 4–9 were observed with a silver core size of 95 nm and silica shell thickness of 5 nm at 0–21% O2. In addition, the intensity enhancement factor increases with increasing core size and decreasing shell thickness in the Ag@SiO2-based oxygen sensors. Using Ag@SiO2 NPs result in brighter emission throughout the 0–21% oxygen concentration. Our fundamental understanding of MEP in the oxygen sensors provides us the opportunity to design and control efficient luminescence enhancement in oxygen and other sensors. .

Exciton-like luminescence of KCl matrix under thermoelastic, local and uniaxial deformation

The radiative relaxation of exciton-like formations in KCl-Na single crystal has been studied by experimental methods of luminescent spectroscopy. The amplifying effect of the radiation intensity with a maximum at 2.8 eV up to 500 times as compared to pure KCl has been detected in KCl-Na. The luminescence efficiency of an exciton-like formation increases with rise in: sodium ions concentration ( 10 ÷ 1000 ppm), thermal exposure ( 500◦C ÷ 600◦C ) and the degree of uniaxial deformation along <100> and <110> crystallographic directions. Previously, such a scale of the luminescence enhancement effect has not been registered in KCl matrix at room temperature. At high sodium concentrations (1000 ppm) in KCl-Na crystals, the additional intense emission with a maximum at 3.1 eV has also been revealed, which is typical for pair sodium ions. It is interpreted that the exciton-like formation in the sodium field with the maximum quantum yield of luminescence is formed by recombination assembly of electron-hole pairs due to the mobility of unrelaxed holes.

Utilization of Judd-Ofelt theory to assess the photophysical properties of β-keto carboxylate Tb(III) complexes with heterocyclic secondary sensitizer

One binary and five ternary green glowing Tb(III) complexes with β-keto acid as primary sensitizer and heterocyclic aromatic system as secondary sensitizer, were synthesised by an eco-friendly method and characterized via various spectroscopic techniques. The assessment of photoluminescent properties in solid complexes and in solution phase with DMSO as solvent, revealed the bright green emission of complexes on irradiation of UV light due to 5D4 → 7F5 transition, whose intensity persistently increased on insertion of secondary sensitizer. Higher relative quantum yield in ternary complexes communicated the contribution of secondary sensitizers in enhancement of luminescence. Judd-Ofelt parameters (Ω2, Ω4, Ω6) were evaluated from NIR absorption spectra of complexes. Higher Ω2 value in complexes demonstrated the higher covalence character and asymmetry around Tb(III) ion. Radiative, nonradiative transition probabilities, radiative life time, branching ratios and luminescence efficiency were also estimated. Complex T6 reported to have 72.5% efficiency which signalizes superb luminescence performance of this complex. Colorimetric parameters were obtained in solid as well as solution form. Exquisite color purity and CCT value > 4000 K established these complexes as cold green light source. Band gap energy and Urbach band tail, obtained via nonlinear fitting of absorption coefficient, turned out to be in semiconductor range thus can have materiality in various photonic devices. The large value of stimulated emission cross section and narrow full width at half maxima (FWHM) of 5D4 → 7F5 emission peak suggested the prospective use of synthesised complexes as laser media for green color lasers.

Bis-Schiff base linkage-triggered highly bright luminescence of gold nanoclusters in aqueous solution at the single-cluster level

Metal nanoclusters (NCs) have been developed as a new class of luminescent nanomaterials with potential applications in various fields. However, for most of the metal NCs reported so far, the relatively low photoluminescence quantum yield (QY) in aqueous solution hinders their applications. Here, we describe the utilization of bis-Schiff base linkages to restrict intramolecular motion of surface motifs at the single-cluster level. Based on Au22(SG)18 (SG: glutathione) NCs, an intracluster cross-linking system was constructed with 2,6-pyridinedicarboxaldehyde (PDA), and water-soluble gold NCs with luminescence QY up to 48% were obtained. The proposed approach for achieving high emission efficiency can be extended to other luminescent gold NCs with core-shell structure. Our results also show that the content of surface-bound Au(I)-SG complexes has a significant impact on the PDA-induced luminescence enhancement, and a high ratio of Au(I)-SG will be beneficial to increasing the photoluminescence intensity of gold NCs.

Enhanced luminescence of Eu-doped films based on gap coupled plasmons

Coupled plasmons are promising candidates for enhancing the luminescence, which can drastically alter the electromagnetic environment of emitters and modulate their emission process. In this paper, we have carried out a comparison of enhanced luminescence based on different plasmonic nanostructures and designed a gap coupled structure Au nanorods (NRs)/space layer/Ag nanoparticles (NPs) film to enhance the photoluminescence (PL) of Eu film. The current result indicates that our maximum enhancement factor is 53.5-fold. And our studies reveal that the Ag NPs film as the substrate provides electromagnetic field enhancement, the space layer as the intermediate layer adjusts the distance to decrease the nonradiative energy transfer. A dominant role of the Au NRs in luminescence enhancement is also indicated due to the perfect match between local surface plasmon resonance (LSPR) of Au NRs and the emission spectrum of Eu. Our designed gap coupled nanostructure has multiple plasmon couplings, which can be beneficial to certain applications such as gap coupled plasmonic nanostructure-based detectors and devices.

Luminescent enhancement of cyan BaSi2O2N2:Eu2+ phosphor by addition of Ho3+

Luminescent enhancement of cyan BaSi2O2N2:Eu2+ phosphor by addition of Ho3+

Non-resonant luminescence enhancement in sol-gel coatings for broadband UV-light conversion on side-emitting optical fibers

Photoluminescence (PL) is a key mechanism for many light conversion applications but often provides only low yield and poor efficiency due to a small interaction cross-section and a relatively narrow range of spectral activity. Here, we present a simple technique to enhance the PL of europium(III) (Eu3+) from sol-gel coatings on the surface of a side-emitting optical fiber. We use small clusters of Ag to boost the emission of Eu3+ by an energy transfer mechanism. The coating's performance is studied as a function of Ag concentration and annealing time. We report a substantial enhancement in Eu3+ emission under resonant and non-resonant excitation with UV light. However, this enhancement vanishes when the Ag clusters grow into larger nanoparticles with plasmon activity: we demonstrate that silver clusters produce stronger amplification with a broader excitation range than metallic nanoparticles. Moreover, these clusters are easily generated and stabilized in a coating using standard sol-gel techniques, suitable for deposition on the surface of side-emitting fibers. Such fibers can then be employed as line-shaped emitters, for example, for structured illumination purposes.

Resonant quenching of photoluminescence in porphyrin-nanocarbon agglomerates

By adopting structural conformations with sub-nanometer precision, nature creates highly concentrated pigment-protein arrays to capture solar energy with high efficiency. Synthetic analogs of such systems exhibit concentration-dependent fluorescence quenching when approaching pigment concentrations of that seen in biological systems. Here, we report on systems of acid-functionalized multi-walled carbon nanotubes and aminophenyl tetraporphyrins that create a novel synthetic pigment-scaffold complex. The complex does not follow the trend of typical fluorescence quenching. Our steady-state and time-resolved data suggest an optimal concentration that offers a luminescence enhancement compared with the expected standard Stern-Volmer quenching relationship. The quenching is modified by controlling the pigment-distance via agglomerate size to near the upper limit for Dexter transfer of 10 Å as confirmed by dynamic light scattering measurements and chromophore-chromophore distance calculations. Our results highlight a synthetic complex with facile synthesis to investigate resonant electron transfer processes that do not follow traditional luminescence self-quenching relationships. • Facile synthesis of porphyrin-nanotube complexes with high attachment in solution • The system presents resonant, bio-analogous luminescence self-quenching • Nanoparticle agglomeration drives chromophore-chromophore transfer mechanism crossover • Interplay of distance-dependent Förster and Dexter transfer mechanism overlap Spencer et al. affix porphyrins to acid-functionalized carbon nanotubes to assess the concentration-based quenching of varying nanotube loadings, finding that agglomeration of the complexes limits energy transfer mechanisms and reduces luminescence quenching. This work reveals detail of a hard-to-study distance-dependent transfer regime change with flexible optical attachments.

Recent Progresses in NIR-II Luminescent Bio/Chemo Sensors Based on Lanthanide Nanocrystals

Fluorescent bio/chemosensors are widely used in the field of biological research and medical diagnosis, with the advantages of non-invasiveness, high sensitivity, and good selectivity. In particular, luminescent bio/chemosensors, based on lanthanide nanocrystals (LnNCs) with a second near-infrared (NIR-II) emission, have attracted much attention, owing to greater penetration depth, aside from the merits of narrow emission band, abundant emission lines, and long lifetimes. In this review, NIR-II LnNCs-based bio/chemo sensors are summarized from the perspectives of the mechanisms of NIR-II luminescence, synthesis method of LnNCs, strategy of luminescence enhancement, sensing mechanism, and targeted bio/chemo category. Finally, the problems that exist in present LnNCs-based bio/chemosensors are discussed, and the future development trend is prospected.

Luminescent properties of spatially ordered Ge/Si quantum dots epitaxially grown on a pit-patterned “silicon-on-insulator” substrate

The results of studying the luminescent properties of epitaxially grown structures with spatially ordered Ge/Si nanoislands (quantum dots), in which the pit-patterned “silicon-on-insulator” substrates serve both for the spatial ordering of quantum dots and for the two-dimensional photonic crystal formation, are presented. It is found that with a certain choice of pit-patterned substrate parameters (diameter of pits and their spatial period), in the photoluminescence spectra of such structures, the multiple narrow peaks are observed. In addition, a significant increase in the quantum dot luminescence signal intensity occurs in the near-infrared range. The effects are related to resonance interaction of quantum dot emitters with photonic crystal modes. The luminescence enhancement effect persists up to room temperatures.

Twinned-Au-tip-induced growth of plasmonic Au–Cu Janus nanojellyfish in upconversion luminescence enhancement

The metallic Janus nanoparticle is an emerging plasmonic nanostructure that has attracted attention in the fields of materials science and nanophotonics. The instability of the Cu nanostructure leads to very complex nucleation and growth kinetics, and synthesis of Cu Janus nanoparticle has challenges. Here, we report a new method for synthesis of Au–Cu Janus nanojellyfish (JNF) by using twinned tips of Au nanoflower (NF) as seeds. The twinned nanotip of the Au NF and the large lattice mismatch between Au and Cu can induce formation of twin defects during the growth process, resulting in asymmetric deposition of Cu atoms. The symmetry-breaking using different sizes of Au NF and Cu nanodomains within the Au–Cu JNF can controllably change the localized surface plasmon resonance (LSPR) modes. The asymmetric Au–Cu JNF can induce plasmon coupling between dipolar and multipolar modes, which leads to clear electric-field enhancement in the near-infrared region. An Au–Cu JNF with multiple LSPR modes was chosen to simultaneously match the excitation and emission bands of the lanthanide-doped upconversion nanoparticles (UCNPs). A 5000-fold enhancement of the upconversion luminescence was achieved by using single plasmonic Au–Cu JNF. The Au–Cu JNF can also provide a guide for new metallic Janus nanoparticles in the fields of plasmonic, photothermal conversion, and nanomotors.

Tunable and Enhanced NIR-II Luminescence from Heavily Doped Rare-Earth Nanoparticles for In Vivo Bioimaging

The last decade has witnessed the booming development of optical imaging in the second near-infrared (NIR-II, 1000-1700 nm) window for disease screening and image-guided surgical interventions, due to the merits of multi-color observations and high spatio-temporal resolution in deep tissue. Therefore, bright and multispectral NIR-II probes are required and play a key role. Here, we report the synthesis of a set of bright rare-earth based NIR-II downshifting nanoparticles (DSNPs) with hexagonal phase (β phase). As compared with the widely reported DSNPs (β-NaYF4@NaYF4:20Yb/(0.5-2)A@NaYF4; A = Ho, Pr, Tm or Er) previously, we reveal that the concentrations of both sensitizers and activators can be further highly doped, not limited by the concentration quenching effect. Our results demonstrate that the optimized formula in the heavily doped DSNPs (β-NaYF4@NaYbF4:A@NaYF4, A = 20Ho, 3Pr, 4Tm or 10Er) leads to 1.2- to 4.2-folds NIR-II luminescence enhancement. Especially for the heavily Er-doped DSNPs with long-wavelength photons extending to the NIR-IIb window (1500-1700 nm), we can further boost their luminescence through introducing a beneficial cross-relaxation and host matrix with higher phonon energy (cubic phase NaYF4@NaYbF4:10Er/5Ce@NaYF4), leading to a total of ∼11.4-fold enhancement. The resulting biocompatible, bright NIR-II emitting DSNPs enable us to in vivo monitor the cerebral vessels through the intact scalp and skull, as well as two-color dynamic tumor imaging with high spatial resolution. This work suggests the potential of the heavily doped DSNPs for multiplexed imaging in cerebrovascular abnormalities toward the diagnosis and therapy of the cerebral diseases.