Mechanism Of Luminescence Enhancement Research Articles

Spectroscopic exploration of upconversion luminescence behavior of rare earth-doped single-particle micro/nanocrystals

In recent years, rare earth-doped upconversion (UC) micro/nanocrystals are useful for many applications, especially in biology because of their unique luminescent properties and specific geometry. The luminescence efficiency of lanthanide-doped UC nanoparticles is of particular importance for their applications. However, the unsatisfactory UC efficiency is still one of the main hurdles. In the present article, a series of Yb3+/Er3+ doped NaYF4 micro/nanoparticles with different ratios of length to diameter are successfully synthesized by a facile hydrothermal route. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) analyses, photoluminescence spectra, and the dynamic process of the luminescence are used to characterize the samples. The intrinsic structural feature of fluoride, the solution pH value, and organic additive Cit3- account for the ultimate shape evolution of the final products. The ratio of length to diameter of NaYF4 microrod can be tuned only by varying the value of pH or the amount of an organic additive (Cit3-). The UC characteristics of a single NaYF4:Yb3+/Er3+ microrod obtained by tuning the value of pH or the amount of Cit3- are investigated by laser confocal microscopy with a 980 nm laser. The two series of codoped fluoride crystals both exhibit the characteristic UC luminescence from Er3+ ions and display the rich luminescence patterns in space. The UC luminescence from a single NaYF4:Yb3+/Er3+ microrod obtained by tuning the value of pH is brighter than that from a single NaYF4:Yb3+/Er3+ microrod with the same size obtained by tuning the amount of Cit3-. The EDX analysis indicates that the number of Na+ defects depends on the specific synthesis conditions of the sample. The Na+ defects of samples obtained by tuning the values of pH are lower than those of samples with the same size obtained by tuning the amount of Cit3-. It conduces to reducing Na+ defects at lower pH value. The parameters of the luminescence kinetics are found to be unambiguously dependent on the size of sample, which relates to higher energy phonon of surface and Na+ defects. The mechanism of luminescence enhancement by pH controlling is explored, and a mechanism based on the reduced intrinsic defects of Na+ is proposed. The investigation not only enriches the controllable synthesis approach of fluoride micro/nanomaterials, but also indicates the potential applications of rare earth materials with a rich luminescence pattern in the photonic devices and anti-counterfeiting devices.

Influence of amino acid sequence in a peptidic Cu+-responsive luminescent probe inspired by the copper chaperone CusF.

Copper(i) is a soft metal ion that plays an essential role in living organisms and Cu+-responsive probes are required to detect Cu+ ions in physiological conditions and understand its homeostasis as well as the diseases associated with its misregulation. In this article, we describe a series of cyclic peptides, which are structurally related to the copper chaperone CusF, and that behave as Cu+-repsonsive probes. These peptide probes comprise the 16-amino acid loop of CusF cyclized by a β-turn inducer dipeptide and functionalized by a Tb3+ complex for its luminescence properties. The mechanism of luminescence enhancement relies on the modulation of the antenna effect between a tryptophan residue and the Tb3+ ion within the probe when Cu+ forms a cation-π interaction with the tryptophan. Here, we investigate the influence of the amino acid sequence of these cyclic peptides on the copper-induced modulation of Tb3+ emission and show that the rigid β-turn inducer Aib-d-Pro and insertion of the Tb3+ complex close to its tryptophan antenna are required to obtain turn-on Cu+ responsive probes. We also show that the amino acid sequence, especially the number and position of proline residues has a significant impact on metal-induced luminescence enhancement and metal-binding constant of the probes.

Multisite luminescence and photocatalytic properties of TiO2:Sm3+ and TiO2:Sm3+@TiO2/TiO2:Sm3+@SiO2 luminescent enhancement materials

Sm3+ doped TiO2 nanocrystals with various morphologies were fabricated via a facile hydrothermal route, and the effect of morphology on the luminescence properties and photocatalytic activity of the products has been investigated. PL studies on TiO2:Sm3+ revealed that the sensitized emission is a much more efficient pathway than the direct excitations of Sm3+. Combined 10 K spectra and theoretical analysis, several kinds of sites of Sm3+ ions have been found in TiO2 matrix. Most importantly, structural models for the formation of multiple sites are proposed based on the optical behaviors of Sm3+ at different sites. Photocatalytic results suggest that flower-like hierarchical architectures show the highest photocatalytic activity compared with nanorods samples with different aspect ratios, and the photodegradation efficiency was 96.8% after 20 min for degradation of methyl orange under white light irradiation. And surface photovoltage spectroscopy (SPV) have been measured to understand the separation and transfer behaviour of photogenerated charges which are helpful for explaining the photocatalytic and luminescence properties deeply. Moreover, TiO2:Sm3+@TiO2 luminescent enhancement homo-structures and TiO2:Sm3+@SiO2 luminescent enhancement hetero-structures are prepared. The effect of calcination temperature on luminescence intensity and the luminescence enhancement mechanism have been discussed in detail.

Understanding the remarkable luminescence enhancement via SiO2 coating on TiO2:Eu3+ nanofibers.

TiO2:Eu3+ nanofibers diameters can be tuned by changing the mixed solvent ratio are synthesized via the electrospinning technique. Concentration quenching phenomena and the relationship of the PL intensity ratio I(5D0-7F2)/I(5D0-7F1) with the Eu doping concentration are discussed. Notably, the luminescence intensity is enhanced by about 7.8 fold by coating SiO2 gel layer on the TiO2:Eu3+ nanofibers, which is successfully performed via a sol-gel process followed by calcination. Furthermore, these fibers are characterized systematically via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectroscopy. Additionally, their Judd-Ofelt and spectral parameters are calculated to investigate their local structures. The relatively low Ω2 value of the coated samples reveals a decrease in covalency in the Eu-O bonds and an increase in the symmetric nature of Eu3+, which indicate that the perturbation effect of the crystal field in the solid system is larger than that of the uncoated samples. FT-IR analysis indicates the formation of Ti-O-Si bonds, which provide the ligand field in the interface between the TiO2:Eu3+ nanofibers and SiO2 layer and can repair the surface unsaturated bonds. This reduces the selection rules for radiative transitions, thereby the state of the Eu3+ ions is converted from dormant to activated. Moreover, the silica coating stabilizes the surface of the TiO2:Eu3+ nanofibers and eliminates the surface defects. Finally, a detailed mechanism is proposed to explain the luminescence enhancement behavior.

Er3+/Yb3+共掺TeO2-WO3-La2O3玻璃中银纳米晶的析出及发光性能

TeO2-WO3-La2O3-AgNO3 glass samples were prepared via melt-quenching method,and the transparent tellurite glasses with Ag nanocrystallites were obtained by heat treatment. The transmittance spectra and stimulated emission spectra of the glass samples with different heat-treatment systems were measured. Ag nanocrystallites in glasses were examined by HR-TEM images,and the luminescence enhancement mechanism was also analyzed. The results show that Ag nanocrystallites are crystallized by heat treatment under 390 ℃ for 15 min. The two-photon absorption process of green and red light in glass does not change after Ag nanocrystallites are introduced. Because of the enhanced local electric field generated by Ag nanocrystallites,the up-conversion and near-infrared luminescence of Ag-contained glass increase,of which the green light intensity of the glass containing Ag nanocrystallites is 5 times as much as that of glass without Ag nanocrystallites.

Preparation of Compensation Ions Codoped SrTiO3:Pr3+ Red Phosphor with the Sol-Gel Method and Study of Its Luminescence Enhancement Mechanism

SrTiO3:Pr3+ is the most representative titanate matrix red phosphor for field emission display (FED). The red luminous efficiency of SrTiO3:Pr3+ will be greatly improved after the compensation ions codoping, so SrTiO3:Pr3+ red phosphor has been a research focus at home and abroad. SrTiO3:Pr3+, SrTiO3:Pr3+, Mg2+, and SrTiO3:Pr3+, Al3+ phosphors are synthesized by a new sol-gel method. Crystal structure, spectral characteristics, and luminescence enhancement mechanism of the sample were studied by XRD and PL spectra. The results showed that after co-doped, SrTiO3:Pr3+ phosphor is single SrTiO3 cubic phase, the main emission front is located at 614 nm, corresponding to Pr3+ ions 1D2→3H4 transition emission. SrTiO3:Pr3+, Mg2+ and SrTiO3:Pr3+, Al3+ phosphor luminescence intensity is enhanced, but the main luminescence mechanism is not changed. Acceptor impurity x = Mg2+, Al3+ will replace Ti bit after being doped into the crystal lattice to form XTi- charge compensation corresponding defect centers PrSr+ to reduce the demand of Sr2+ or Ti3+ vacancy. While Sr-doped Pr will make lattice distortion and transition energy of 4f-5d is very sensitive to crystal electric field changes around Pr atom. Doping different impurities will make electric field distribution around the icon have a different change. It increases energy transfer of 4f-5d transition and improves the luminous intensity of SrTiO3:Pr3+ red phosphor.

Luminescence Enhancement Mechanism of Lanthanide-Doped Hybrid Nanostructures Decorated by Silver Nanocrystals

Hybrid nanostructures composed of rare earth ion-doped lanthanum trifluoride nanocrystals deposited on silica nanospheres (LaF3:Yb3+, Er3+@SiO2) and decorated with varying quantities of silver nanoparticles (Ag NPs) were synthesized using a simple strategy. Down and upconversion luminescence spectra were recorded. The luminescence dynamics were also recorded following excitation with a 532-nm pulse. Silver loading was found to have a significant effect both on the luminescence intensity and the luminescence decay rate, with the samples with the lowest silver content showing reduced luminescence intensity over silver-free samples, while the samples with large levels of silver loading showed significant luminescence enhancement. The results were successfully (and quantitatively) interpreted in terms of the competition between surface plasmon-induced field enhancement mediated by the Ag nanoparticles and nonradiative energy transfer from the luminescent ions to Ag nanoparticles. By combining the measured luminescence intensity with the luminescence decay rate determined from the dynamics measurements, and with the measured surface plasmon absorption spectra, one could obtain a quantitative and self-consistent understanding of the observed dependence of the green 4S3/2→4I15/2 (~540 nm) and red 4F9/2→4I15/2 (~650) emission bands on the Ag NP metal loading.

Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: A new luminescent uranyl benzoate specie

Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV–Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3]− which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68μs which is much more compared to the lifetime of uncomplexed uranyl (20μs) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3]− specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.

Luminescence Enhancement of Samarium-Doped Tellurite Glass Containing Silver Nanoparticles

Samarium-doped tellurite glass embedded with silver nanoparticles are synthesized by melt quenching technique and optically characterized. The effect of silver nanoparticles on the luminescent properties of the samarium-doped sodium tellurite glass is investigated. Upon pumping with 406 nm radiation, it is found that there are four distinctive emission bands centered at 562 nm, 599 nm, 645 nm and 705 nm. In the presence of silver nanoparticles in the glass substrates, we observe significant enhancement in the intensity of these emission bands. The enhancement tends to increase with the increasing of silver nanoparticles concentration. The mechanism of luminescence enhancement is discussed in terms of localized surface plasmon resonance.

Luminescence Spectra of Erbium Doped Zinc Tellurite Glass Embedded with Gold Nanoparticles

Understanding the mechanism of visible luminescence enhancement from rare earth doped glasses containing metallic nanoparticles (NPs) is the challenging issue. The photoluminescence (PL) spectra of Er3+: Au-doped tellurite glass is investigated for different concentration of gold NPs. A series of glasses with composition (70-x) TeO2-30 ZnO-0.5 Er2O3x Au where x = (0.1, 0.3, 0.5 mol%) are prepared by melt-quenching method. The thermal parameters such as the glass transition (Tg), crystallization temperature (Tc) and melting temperature (Tm) are determined using DTA thermogram. PL spectra exhibit two distinct peaks at 493nm and 550nm which are assigned to the2H11/2-4I15/2and4S3/2-4I15/2transition respectively. The influence of gold NPs in enhancing the luminescence intensity under the 360nm excitation wavelength is observed understood.

Optimized upconversion emission of NaLuF4:Er,Yb nanocrystals codoped with Gd3+ ions and its mechanism

NaLu(Gd)F4:Yb,Er nanocrystals (NCs) with different Gd3+ concentrations were synthesized, and the luminescence enhancement mechanism under excitation at 980nm is discussed. The optimized concentration of Gd3+ ions in NaLuF4:Yb,Er NCs is 20%, of which the upconversion emission is nearly 10times stronger than that of the Gd3+-free sample. In addition, the optimized concentration indicates a good balance between phase-transition and concentration quenching.

The real role of active-shell in enhancing the luminescence of lanthanides doped nanomaterials

Although it is widely recognized that doping sensitizers in the shell can improve significantly the luminescence of lanthanides doped nanocrystals, lack of an unambiguous picture of relevant luminescence enhancement mechanism seriously hinders the optimization of this approach. In this work, the complete processes of excitation energy migration, from photon absorption to emission, was dissected to unravel the role of sensitizers doped in shell in every individual stage. We revealed that the essence of doping sensitizers in the shell is just to increase the absorption efficiency whereas the quantum yield is lessened simultaneously. The optimal sensitizer doping concentration is also fixed to achieve the best luminescence performance.

Investigation on the co-luminescence effect of europium (III)-lanthanum(III)-dopamine-sodium dodecylbenzene sulfonate system and its application

A novel luminescence, enhancement phenomenon in the europium(III)-dopamine-sodium dodecylbenzene sulfonate system was observed when lanthanum(III) was added. Based on this, a sensitive co-luminescence method was established for the determination of dopamine. The luminescence signal for the europium (III)-lanthanum(III)-dopamine-sodium dodecylbenzene sulfonate system was monitored at λ(ex) = 300 nm, λ(em) = 618 nm and pH 8.3. Under optimized conditions, the enhanced luminescence signal responded linearly to the concentration of dopamine in the range 1.0 × 10(-10)-5.0 × 10(-7) mol/L with a correlation coefficient of 0.9993 (n = 11). The detection limit (3σ) was 2.7 × 10(-11) mol/L and the relative standard deviation for 11 parallel measurements of 3.0 × 10(-8) mol/L dopamine was 1.9%. The presented method was successfully applied for the estimation of dopamine in samples of pharmaceutical preparations, human serum and urine. The possible luminescence enhancement mechanism of the system is discussed briefly.

Preparation and luminescence properties of Tb3+ doped SiO2 film on TiO2 nanotube arrays

TiO2 nanotube arrays (TiO2 NTs) are fabricated by anodic oxidation of titanium in NH4Cl+H2O and NH4F+HOCH2CH2OH electrolytes respectively, then TiO2 NTs coated with Tb3+ doped SiO2 films (Tb–SiO2/TiO2 NTs) are prepared by sol–gel method and dip-coating process. The luminescence properties of Tb–SiO2/TiO2 NTs are investigated by fluorescence spectrometer. Results show that TiO2 NTs can improve the luminescence properties of Tb–SiO2, especially the TiO2 NTs fabricated in NH4Cl+H2O electrolyte. The emission intensity of Tb–SiO2 on the TiO2 NTs fabricated in NH4Cl+H2O electrolyte is five times to that on the pure titanium sheet. Additionally, the effect of TiO2 NTs preparation conditions on the Tb–SiO2 luminescence properties is analyzed in detail, and the luminescence enhancement mechanism of Tb–SiO2 on TiO2 NTs is explained.

A new quaternary luminescence enhancement system of Eu–N-(3-methoxysalicylidene)-2-aminopyridine–1,10-phenanthroline–Zn and its application in determining trace amounts of Eu3+ and Zn2+

Abstract A new sensitive quaternary luminescence enhancement system was developed successfully to determine the trace amounts of Eu 3+ and Zn 2+ . The luminescence intensity of Eu–N-(3-methoxysalicylidene)-2-aminopyridine system was greatly increased by the addition of 1,10-phenanthroline and Zn 2+ . The excitation and emission wavelengths were 274 and 617 nm, respectively. Under optimal conditions, the luminescence intensity of the system showed a linear response toward Eu 3+ in the range of 6.0 × 10 −6 –2.5 × 10 −5 mol L −1 with a detection limit of 2.0 × 10 −9 mol L −1 . This method was successfully applied for the determination of trace amounts of Eu 3+ in a high purity Gd 2 O 3 matrix and a synthetic matrix. In addition, it was found that under optimal conditions, the luminescence intensity of the system decreased linearly with the increase of Zn 2+ concentration, ranging from 2.0 × 10 −6 to 1.8 × 10 −5 mol L −1 with a detection limit of 2.8 × 10 −8 mol L −1 . This method was also successfully applied to determine the trace amounts of Zn 2+ in a high purity Mg(NO 3 ) 2 ·6H 2 O matrix and a synthetic sample. The interferences of other lanthanide ions and some common coexisting ions were investigated. The mechanism for energy transfer and luminescence enhancement of this quaternary system was also studied systematically.

Evaluation of acetylcysteine promoting effect on CdTe nanocrystals photoluminescence by using a multipumping flow system

A simple and straightforward quantification method integrated in a fully automated multi-pumping flow system (MPFS) using water-soluble mercaptopropionic acid (MPA)-capped CdTe quantum dots (QDs) was implemented for the fluorescence quantification of N-acetyl-l-cysteine (NAC) in pharmaceutical formulations. The developed approach was based on NAC ability to establish surface interactions that result in enhanced nanocrystals fluorescence intensity, proportional to analyte concentration. Size and concentration of QDs, ageing, composition, concentration and pH of the buffer solution revealed to have a noticeable effect on the enhancing efficiency affecting sensitivity and linear working range of the methodology.Under the optimal conditions, a linear working range was obtained for NAC concentrations ranging from 50 to 750μmolL−1 (r=0.9978), with good precision (r.s.d.<1.6%; n=5) and a sampling rate of about 75hr−1. The detection limit (LOD) was approximately 1.6μmolL−1. The method was applied to pharmaceutical preparations and the results revealed good agreement with those obtained by the reference procedure with relative deviations between −2.1 and +4.2%. Advantages of the new procedure include speed, low consumption of reagents, minor waste generation, requiring also much less work than the recommended HPLC method. The mechanism for luminescence enhancement of CdTe QDs is discussed. FT-IR spectra revealed that sulphydryl groups of NAC have a high affinity with the nanocrystals.

A small-molecular europium complex with anion sensing sensitivity

A novel small-molecular europium(III) complex with quinoline derivative has been designed and prepared for anion recognition. This Eu(3+) complex displays striking emission changes at 616 nm in response to NO(3)(-) and Cl(-). What's more, the anion-selective luminescence enhancement is easily detected by the naked eye. UV, luminescence titration experiments and the Job plot analysis revealed that the ligand can form stable 1 : 1 complexes with Eu(NO(3))(3) or EuCl(3) in CH(3)CN; log K = 7.10 and 6.76 (295 K), respectively. The crystal structure shows that three oxygen atoms and one nitrogen atom of the ligand are approximately coplanar and wrap around the Eu(3+) ion through a semicircle-shaped coordination structure and some unoccupied sites of the central europium ions are available for guest anions in the complexes. Thus, three nitrate ions are located in the gap of the semicircle. It is supposed that the mechanism of luminescence enhancement is of NO(3)(-) or Cl(-) anions squeezing out solvent molecules from the inner coordination sphere.

GeO2 dopant induced enhancement of red emission in CaAl12O19:Mn4+ phosphor

In order to search efficient red-emitting phosphors for white LEDs application, CaAl12O19:Mn4+ phosphors have been prepared by a combustion method assisted with GeO2 flux. The influence of GeO2 concentration and annealing temperature on the structure and luminescence intensity for the phosphors has been investigated. The mechanism for luminescence enhancement has been discussed. At GeO2 doping concentration of 1.5 mol%, the red emission intensity increases by 81% under 330 nm UVA excitation. More isolated luminescence center Mn4+ ions rather than pairs of Mn4+–Mn2+ ions are formed in the lattice with the introduction of GeO2 at high temperature oxidation, leading to the enhancement of the red emission. A feasible new way to enhance the red emission in CaAl12O19:Mn4+ phosphor is obtained.

Luminescent properties of dye–PMMA composite nanospheres

The luminescent properties of two types of dye-poly(methyl methacrylate) (PMMA) composite nanospheres were discussed and compared. Dye molecules (Ru(bpy)(3)Cl(2)) were combined with PMMA nanospheres in two strategies: embedding dye molecules during PMMA nanosphere formation (Em-PMMA NPs) and adsorbing dye molecules onto the surface of the produced PMMA nanospheres (Ad-PMMA NPs). It has been proved that the electrostatic interaction dominated the load of Ru(bpy)(3)(2+) on the PMMA matrix. The luminescence intensity of the Em-PMMA NPs was much higher than that of the Ad-PMMA NPs under same dye concentration due to different dye load distribution in two types of dye-PMMA composite nanospheres. Luminescence lifetime measurement of Ru(bpy)(3)(2+) in the Em-PMMA NPs (containing 2.20 × 10(3) Ru(bpy)(3)(2+) molecules per NP) indicates that ∼60% of dye molecules loaded in inside of the PMMA matrix and ∼40% located close to/on the surface of NPs. For the Ad-PMMA NPs containing same amount of dye as Em-PMMA Nps, most of dye molecules (∼84%) were on the surface of NPs and only ∼16% of them penetrated into the PMMA matrix. The luminescence of the Em-PMMA NPs had nearly seven fold enhancement and the excited-state lifetime had nearly five fold extension relative to a dye aqueous solution. The mechanism of luminescence enhancement was studied. The results indicate that the larger viscosity and weaker polarity of a PMMA matrix led to the luminescence enhancement of Ru(bpy)(3)(2+). These luminescent PMMA nanospheres with high stability, long lifetime and high brightness hold great the potential for being a novel biological label.

Luminescence Enhancement Mechanism of ZnGa2O4 Phosphor Screen with an In2O3 Buffer Layer

The luminescence enhancement mechanism of a white phosphor screen with an buffer layer was studied by growing with optimal sputtering parameters and varying the deposition conditions of . A film with better crystallization and smaller grains was obtained when it was deposited on . These qualities revealed that the resistivity of the phosphor screen was correlated with the surface roughness and resistivity of the buffer layer. The photoluminescence spectra of the phosphor screen revealed that the ligand field of the Ga luminescence center was not modified when the deposition parameters were varied; however, the emission intensities were altered due to the electron-transition probability in the Ga energy levels changing with the crystallization of phosphor. A significantly enhanced emission from the phosphor screen was observed by improving the crystallization, surface morphology, and resistivity of the prepared phosphor film with the buffer layer.