Absolute Luminescence Quantum Research Articles

Size Growth of Au4Cu4: From Increased Nucleation to Surface Capping.

The size conversion of atomically precise metal nanoclusters is fundamental for elucidating structure-property correlations. In this study, copper salt (CuCl)-induced size growth from [Au4Cu4(Dppm)2(SAdm)5]+ (abbreviated as [Au4Cu4S5]+) to [Au4Cu6(Dppm)2(SAdm)4Cl3]+ (abbreviated as [Au4Cu6S4Cl3]+) (SAdmH = 1-adamantane mercaptan, Dppm = bis-(diphenylphosphino)methane) was investigated via experiments and density functional theory calculations. The [Au4Cu4S5]+ adopts a defective pentagonal bipyramid core structure with surface cavities, which could be easily filled with the sterically less hindered CuCl and CuSCy (i.e., core growth) (HSCy = cyclohexanethiol) but not the bulky CuSAdm. As long as the Au4Cu5 framework is formed, ligand exchange or size growth occurs easily. However, owing to the compact pentagonal bipyramid core structure, the latter growth mode occurs only for the surface-capped [Au4Cu6(Dppm)2(SAdm)4Cl3]+ structure (i.e., surface-capped size growth). A preliminary mechanistic study with density functional theory (DFT) calculations indicated that the overall conversion occurred via CuCl addition, core tautomerization, Cl migration, the second [CuCl] addition, and [CuCl]-[CuSR] exchange steps. And the [Au4Cu6(Dppm)2(SAdm)4Cl3]+ alloy nanocluster exhibits aggregation-induced emission (AIE) with an absolute luminescence quantum yield of 18.01% in the solid state. This work sheds light on the structural transformation of Au-Cu alloy nanoclusters induced by Cu(I) and contributes to the knowledge base of metal-ion-induced size conversion of metal nanoclusters.

A novel red emitting NaBa12B7O21F4:xEu3+phosphor: Synthesis, structure and luminescence properties

NaBa12B7O21F4:xEu3+ phosphors, where 0 < x ≤ 0.16, were obtained through the high temperature solid phase reaction method. The phosphors showed significant red fluorescence emission resulting from the dominant 5D0→7F2 transitions. The optimum doping concentration of Eu3+ ions in the NaBa12B7O21F4 matrix were estimated to be 14 mol%. The phenomenon of concentration quenching was researched, and the concentration quenching of NaBa12B7O21F4:xEu3+ phosphors maybe caused by the exchanging interaction of Eu3+ ions. Moreover, it was found that the optimal-component NaBa12B7O21F4:0.14Eu3+ phosphor showed high absolute luminescence quantum efficiency and had a millisecond fluorescence lifetime.

A Class of Biocompatible Dye-Protein Complex Optical Nanoprobes.

Molecular organic dyes are classic fluorescent nanoprobes finding tremendous uses in biological and life sciences. Yet, they suffer from low brightness, poor photostability, and lack of functional groups for bioconjugation. Here, we describe a class of biocompatible dye-protein optical nanoprobes, which show long-time photostability, superbrightness, and enriched functional groups. These nanoprobes utilize apoferritin (an intracellular protein for iron stores and release) to encase appropriate molecular organic dyes to produce on-demand fluorescence in aqueous solution. A pH-driven dissociation-reconstitution process of apoferritin subunits allows substantial incorporation of hydrophilic (aggregation caused quenching, ACQ) or hydrophobic (aggregation induced enhancement, AIE) dye molecules into the protein nanocavity (8 nm), producing monodispersed dye-apoferritin nanoparticles (apo-dye-NPs, ∼12 nm). As compared with single dye monomer, single apo-dye-NPs possess hundreds of times larger molar extinction coefficient and 2 orders of magnitude higher absolute luminescence quantum yield (up to 45-fold), multiplying fluorescence brightness up to 2778-fold. We show that varying the type of incorporated dyes entails a precise control over nanoprobe emission profile tunable in a broad spectral range of 370-1300 nm. Mechanical investigations indicate that the diversified microstructures of nanocavity inner surface are able to conform ACQ dyes at reasonable space interval while providing protein-guided-stacking for AIE dyes, thus enhancing fluorescence quantum yield through confining intermolecular quenching and intramolecular rotation. Moreover, apo-dye-NPs are able to emit stable fluorescence (over 13 min) without quenching in confocal imaging of HepG2 cancer cell under ultrahigh laser irradiance (1.3 × 106 W/cm2). These superb properties make them suitable, as demonstrated in this work, for long-term super-resolved structured illumination microscopic cell imaging (spatial resolution, 117 nm) over 48 h, near-infrared (NIR) fluorescence angiography imaging of whole-body blood vessels (spatial resolution, 380 μm), and NIR photoacoustic imaging of liver in vivo.

Optical properties of composites based on polyethylene and monoclinic Y2O3:Eu3+ nanoparticles

Polyethylenem-Y2O3:Eu3+ composites (PECs) containing 0.32, 0.77, and 1.79 wt% of well-dispersed sphere-like m-Y2O3:Eu3+ nanoparticles were obtained by in situ polymerization in the presence of a titanium-magnesium catalyst (TMC). TMC was synthesized by sequential deposition of organic magnesium and TiCl4 on m-Y2O3:Eu3+ that had been previously dehydroxylated at 650 °C. Detailed photoluminescence properties of the obtained composites as a function of m-Y2O3:Eu3+ content were investigated in combination with UV–Vis and IR spectroscopy data. It was shown that Eu3+ ions in monoclinic Y2O3 lattice are responsible for the high red emission of the composites. The effect of the РЕС host on the luminescence properties of m-Y2O3:Eu3+ was revealed. The obtained chromaticity coordinates with improved red color (0.653, 0.347) and high absolute luminescence quantum yield up to 23% make РЕСs potential promising materials for luminescent applications.

Zn(II) cation-induced solution emission of 4-(4-(1,2,2-triphenylvinyl)phenyl)benzoic acid: Intuitionistic evidence of RIM mechanism

4-(4-(1,2,2-triphenylvinyl)phenyl)benzoic acid (TPEPhCOOH) with Zn2+ ion induced solution emission (CISE) character was synthesized. The freshly prepared TPEPhCOOH film has the fluorescence (FL) at ca. 498 nm with the excited-state decay lifetime of 2.98 ns and the absolute luminescence quantum yield of 64.8%. The FL studies on the non-radiative TPEPhCOOH/THF solutions with different metal ions suggest that TPEPhCOOH could radiatively response to the presence of Zn2+ ions. The aggregation-induced emission character of TPEPhCOOH in the mixed water/THF solvent (ca. 10−5 mol/L), along with the molecular dynamic and the quantum mechanic calculations, suggests that the Zn2+ CISE of TPEPhCOOH should originate from the coordination between Zn2+ ions and the TPE moiety of TPEPhCOOH.

Effects of Different Eelectron-withdrawing Moieties on the General Photoelectric Properties of Fluorene-based Dimers

Here, 9,9,9′-tris(4-butoxyphenyl)-9H-9′H-2,2′-difluorene(DF) was synthesized as a reference for comparison, and diphenyl sulfone and triphenylphosphine oxygen were introduced to the 9-position of fluorene through a C-H coupling reaction to produce two fluorene-based oligomers 9′,9′″-[sulfonylbis(4,1-phenylene)]bis[9,9,9′-tris-(4-butoxyphenyl)-9H,9′H-2,2′-bifluorene](DF)2SO2 and phenylbis(4-{9,9′,9′-tris(4-butoxyphenyl)-9H,9′H-[2,2′-bifluorene]-9-yl}phenyl)phosphine oxide[(DF)2PO]. Solid powders of all the three compounds exhibit excellent thermal stability with thermal temperature at 5% mass loss of 375, 429 and 383 °C for (DF)2SO2, (DF)2PO and DF. In addition, owing to the distorted molecular structure and weak electron-absorbing ability of the acceptor, (DF)2SO2 and (DF)2PO do not have obvious intramolecular charge transfer characteristics, and exhibit stable localized 394 nm/375 nm fluorescence emission peaks in different polar solvents. The absolute luminescence quantum efficiencies of (DF)2SO2, (DF)2PO and DF solid powders are 20.83%, 10.03% and 59.46%. Compound DF has the highest quantum yield as an electron donor. The chromaticity coordinates of the blue OLED devices based on DF and DF2SO2 fabricated by solution spin coating were (0.19, 0.10) and (0.19, 0.11), which were closest to the deep blue region, and the corresponding maximum external quantum efficiencies are 1.45% and 0.87%, respectively, which are higher than that of (DF)2PO(0.25%) and consistent with the difference in the solid-state quantum efficiency between them.

Absolute luminescence quantum yield for nanosized carbon particles in water as a function of excitation wavelength.

The absolute luminescence quantum yield Q as a function of excitation wavelength λex in a wide spectral range 270-470nm was measured for the first time for the group of carbon nanoparticles dispersed in water: carbon dots (CD), detonation nanodiamonds (DND), as well as detonation nanodiamonds decorated with carbon dots (CD-DND). The luminescence quantum yield for DND increased after functionalization; the CD-decorated DND demonstrated significantly higher Q values in the UV region of excitation. We found that the quantum yield for CD luminescence is 4-8 times higher than that for CD-DND luminescence, and 20 times higher than that for DND luminescence. Roughly three spectral regions can be distinguished within the Q(λex): below 330nm, 330-390nm and 390-470nm. Conclusions are drawn about the number of chromophores of the studied nanoparticles and transfer of photoexcitation energy in the systems under consideration.

Efficient Ytterbium Near-Infrared Luminophore Based on a Nondeuterated Ligand.

A novel molecular ytterbium complex is reported with a new tetradentate ligand based on the 2,2'-bipyridine-6,6'-dicarboxylic acid scaffold. The photophysical properties are investigated, especially with respect to near-infrared luminescence. The ytterbium complex shows a rather high absolute luminescence quantum yield of Φ = 3.0% and a luminescence lifetime of τobs = 72 μs at room temperature in CD3OD solution.

Luminescent properties of new red emitting fluoborate based phosphors, Na3Ba2-xB6O12F:xEu3+

A series of Na3Ba2-xB6O12F:xEu3+ (x = 0.03, 0.05, 0.08, 0.10, 0.13, 0.16, 0.17, 0.19, 0.20 and 0.22) phosphors were prepared by the high temperature solid state reaction method. The single crystal-phase Na3Ba2B6O12F of the Na3Ba2-xB6O12F:xEu3+ sample was confirmed by X-ray powder diffraction measurement. The optical properties are evaluated by photoluminescence excitation and emission spectra, CIE chromaticity coordinate and decay curve. Na3Ba2-xB6O12F:xEu3+ phosphors present the red emitting color under the excitation of near-UV light around 395 nm. Investigation of Eu3+ content dependent emission spectra indicates that x = 0.19 is the optimum doping content of Eu3+ ions in the Na3Ba2B6O12F host. Moreover, the critical distance and the concentration quenching mechanism were also investigated. The absolute luminescence quantum efficiency and the decay time of Na3Ba1.81B6O12F: 0.19Eu3+ sample were reported.

Making graphene luminescent by adsorption of an amphiphilic europium complex

We fabricated luminescent chemical vapor deposition-grown monolayer graphene sheets with an adsorbed europium complex, EuLC18, and characterized their luminescence properties. The EuLC18/graphene sheets clearly showed several photoluminescence peaks in a wavelength region from 580 to 694 nm, which were attributed to the ff transitions of the Eu ion. Luminescence was obtained via a photo-antenna effect, in which the ligands of EuLC18 absorbed the photo-excitation energy and transported it to the Eu excitation. Although the absolute luminescence quantum yield of the EuLC18/graphene sheet was as low as 0.5% due to the interaction between graphene and EuLC18, we demonstrated that graphene sheets can be made luminescent simply through adsorption of the luminescent Eu complex on the graphene surface.

Derivatives of 1-benzyl-4-(4-triphenylvinylphenyl) pyridinium bromide: Synthesis, characterization, mechanofluorochromism/aggregation-induced emission (AIE) character and theoretical simulations

4-(4-triphenylvinyl phenyl) pyridine (TPEPy) was used, along with the benzile bromide derivatives, to prepare 1-benzyl-4-(4-triphenylvinyl phenyl) pyridinium bromide (1) and its derivatives by replacing the benzyl bromide with 4-cyanobenzyl bromide for 2, 4-nitrobenzyl bromide for 3 and 4-trifluoromethyl benzyl bromide for 4, respectively. The maxima of the photoluminescent (PL) spectra of the freshly prepared powder samples of 1 ~ 4 are in the range of 510nm ~ 530nm with the absolute luminescence quantum yields (ALQY) of 88.10% for 1, 4.69% for 2, 1.70% for 3 and 36.30% for 4, respectively, which would redshift to the range of 554nm ~ 571nm with ALQYs of 54.70% for 1, 41.00% for 2, 14.70% for 3 and 43.40% for 4, respectively, after they are ground. At the same time, 1 ~ 4 have no obvious PL bands in dichlormethane solution (10-5mol/L) until ≥ 80% n-hexane was added. Finally, the ground-state geometries and the UV-Vis absorption spectra of 1 ~ 4 were simulated at B3LYP/6-31G(d,p) level to theoretically explain their photophysical behaviors.

Luminescent properties of cadmium selenide quantum dots in fluorophosphate glasses

The optical properties of fluorophosphate glasses with CdSe quantum dots are studied. Secondary heat treatment at a temperature exceeding the glass transition temperature resulted in the formation of quantum dots with sizes of 3.7–6.2 nm. The influence of the semiconductor component concentration on the spectral-luminescent characteristics of glasses is shown. It is experimentally demonstrated that glasses with a lower CdSe concentration have a higher absolute luminescence quantum yield.

Vibrational and luminescent properties of LaPO4:Eu3+ with different preparation conditions

Monoclinic and hexagonal LaPO4:5 mol.%Eu3+ phosphors were synthesized with merely adjusting pH values of solutions by a hydrothermal method at the same synthesis temperature. The microstructure, morphology and photoluminescence of Eu3+-doped LaPO4, which were influenced by different preparation conditions, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and luminescence spectroscopy, respectively. The specimen showed monoclinic structure in strong acid solution, however, it changed into hexagonal structure in weak acid solution and strong alkali solution. The monoclinic LaPO4:Eu3+ showed the longest length to diameter ratio, which was attributed to the preferential growth of [-112]. The monoclinic specimen exhibited a slight red shift in infrared spectra, Raman band positions and charge transfer (CT) compared with hexagonal specimens. Moreover, the calculated results of grain sizes, lattice parameters, full width at half maximum in Raman patterns and emission integral intensity were in good agreement with analysis results. The monoclinic specimen showed the maximal absolute luminescence quantum yield (0.4) and the second lifetime τ2 (0.52 ms), which was accordant with red-orange emission in CIE. The 5D0→7F1 occupied a dominate position in hexagonal specimens, which indicated that more Eu3+ in the hexagonal structure were occupied inversion center of symmetry sites.

Uniform Terbium Coordination Polymer Microspheres: Preparation and Luminescence

Uniform terbium coordination polymer microsphere particles are synthesized via a facile solvothermal method, using 3-methyl benzoic acid (3-MeBAH) as ligand. The products were characterized by SEM, PXRD, EA, FT-IR, downconversion and upconversion luminescence. PXRD result confirms that sample 1 has one dimensional structure, which is constructed by dinuclear second building unit. The effect factors of reaction temperature and reaction time in synthesizing the uniform microsphere particles were investigated in detail. Downconversion luminescence research shows the sample 1 exhibits characteristic transitions at 488, 544, 585, 621 and 636 nm, which corresponding to the transitions of 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, 5D4 → 7F3 and 5D4 → 7F2 of Tb3+ respectively, and the strongest peak is at 544 nm. The absolute luminescence quantum yield of sample 1 is as high as 32.7 %. Furthermore, investigation indicates the upconversion luminescence of sample 1 is the two-photo absorption of the ligand.

Strong room-temperature blue-violet photoluminescence of multiferroic BaMnF4.

BaMnF4 microsheets have been prepared using a hydrothermal method. Strong room-temperature blue-violet photoluminescence has been observed (an absolute luminescence quantum yield of 67%) with two peaks located at 385 nm and 410 nm. More interestingly, photon self-absorption phenomenon has been observed, leading to an unusual abrupt decrease in the luminescence intensity at a wavelength of 400 nm. To understand the underlying mechanism of such emission, the electronic structure of BaMnF4 has been studied using first principles calculations. The observed two peaks are attributed to electron transitions between the upper-Hubbard bands of the Mn's t2g orbitals and the lower-Hubbard bands of the Mn's eg orbitals. The Mott gap mediated d-d orbital transitions may provide additional degrees of freedom to tune the photon generation and absorption in ferroelectrics.

Synthesis and luminescence characterization of Eu3+-activated Na3La8V3O21 as a red-emitting phosphor

A new red-emitting phosphor of Eu3+-doped Na3La8V3O21 was successfully synthesized by the high-temperature solid state reaction. The phase formation was confirmed by X-ray powder diffraction (XRD) analysis. The morphology of the phosphor was analyzed by scanning electron microscopy (SEM). The optimal doping concentration of Na3La8V3O21:Eu3+ is about 20mol%. The detailed luminescence properties, e.g., the excitation spectra, the luminescence spectra and quantum efficiency under the excitation of near-UV, and decay lifetimes were reported. The phosphors can be efficiently excited by near-ultraviolet light and exhibit a bright red luminescence around 618nm ascribed to the forced electric dipole transition 5D0→7F2 of Eu3+ ions. The thermal stabilities and the absolute luminescence quantum efficiency (QE) were reported. The phosphors of Eu3+-activated Na3La8V3O21 have been discussed as a candidate for white solid state lighting indicating.

Absolute phosphorescence quantum yields of singlet molecular oxygen in solution determined using an integrating sphere instrument.

In this paper, we present an integrating sphere instrument for absolute luminescence quantum yield measurements from the visible to near-infrared (NIR) spectral region (λ = 350-1650 nm). The integrating sphere is equipped with a Xe light source and two spectrally corrected multichannel analyzers using a back-thinned charge-coupled device (CCD) and InGaAs detector, one for measurements in the visible to NIR wavelength region (λ = 350-1100 nm) and the other for the NIR wavelength region (λ = 900-1650 nm). The combination of the two optical multichannel analyzers allows measurement of the absolute quantum yield of NIR emissions with good sensitivity. Using this new instrument and platinum(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP) as a sensitizer, we performed the first absolute measurements of quantum yield (Φ(p)(¹Δ)) of the a¹Δ(g) (v′ = 0) → X³Σ(g)⁻ (v″ = 0) emission at 1270 nm from molecular oxygen in different solvents. The quantum yields Φ(p)(¹Δ) in CCl₄ and CS₂ under infinite dilution of sensitizer were determined to be 2.2 × 10⁻² and 6.4 × 10⁻², respectively. Using the Φ(p)(¹Δ) value in CCl₄, the quantum yields in other solvents were determined based on the relative method. From the phosphorescence quantum yields and the lifetimes of O₂(a¹Δ(g)) taken under identical experimental conditions, we evaluated the radiative and nonradiative rate constants of O₂(a¹Δ(g)), which are key parameters to understand the photophysical properties of singlet oxygen in solution. The quantum yields and radiative and nonradiative rate constants obtained in the present study were compared with the literature values determined based on the relative method.

Role of electron transfer in Ce3+ sensitized Yb3+ luminescence in borate glass

In a Ce3+-Yb3+ system, two mechanisms are proposed so far namely, the quantum cutting mechanism and the electron transfer mechanism explaining Yb3+ infrared luminescence under Ce3+ excitation. Among them, the quantum cutting mechanism, where one Ce3+ photon (ultraviolet/blue) gives rise to two Yb3+ photons (near infrared) is widely sought for because of its huge potential in enhancing the solar cell efficiency. In present study on Ce3+-Yb3+ codoped borate glasses, Ce3+ sensitized Yb3+ luminescence at ∼1 μm have been observed on Ce3+ 5d state excitation. However, the intensity of sensitized Yb3+ luminescence is found to be very weak compared to the strong quenching occurred in Ce3+ luminescence in Yb3+ codoped glasses. Moreover, the absolute luminescence quantum yield also showed a decreasing trend with Yb3+ codoping in the glasses. The overall behavior of the luminescence properties and the quantum yield is strongly contradicting with the quantum cutting phenomenon. The results are attributed to the energetically favorable electron transfer interactions followed by Ce3+-Yb3+ ⇌ Ce4+-Yb2+ inter-valence charge transfer and successfully explained using the absolute electron binding energies of dopant ions in the studied borate glass. Finally, an attempt has been presented to generalize the electron transfer mechanism among opposite oxidation/reduction property dopant ions using the vacuum referred electron binding energy (VRBE) scheme for lanthanide series.

Switching-on quantum size effects in silicon nanocrystals.

The size-dependence of the absolute luminescence quantum yield of size-separated silicon nanocrystals reveals a "volcano" behavior, which switches on around 5 nm, peaks at near 3.7-3.9 nm, and decreases thereafter. These three regions respectively define: i) the transition from bulk to strongly quantum confined emissive silicon, ii) increasing confinement enhancing radiative recombination, and iii) increasing contributions favoring non-radiative recombination.

Coprecipitation synthesis, structure and photoluminescence properties of Eu3+-doped sodium barium borate

Micro-sized phosphors of Eu3+-doped NaBaBO3 (0.5–12mol%) were prepared by the modified co-precipitation synthesis. The samples were characterized by scanning electron micrograph (SEM) images and electron dispersive X-ray (EDX). The polycrystalline samples are well developed to the regular plate-like particles with the uniform morphology. The single crystal-phase NaBaBO3 of the Eu3+-doped sample was confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The optical properties are evaluated by photoluminescence (PL) excitation and emission spectra, and decay curves. The absolute luminescence quantum efficiency (QE) and the activation energy (ΔE) are reported. Eu3+-doped NaBaBO3 presents a bright red-emitting color under the excitation of near-UV light around 400nm. The maximum absolute QE of NaBaBO3:Eu3+ is estimated to be 53% at 300K. The phosphor shows an excellent thermal stability on temperature quenching effects. The results were discussed on the relationship between the structure and the luminescence properties.