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A Single 808 nm Near-Infrared Light-Mediated Multiple Imaging and Photodynamic Therapy Based on Titania Coupled Upconversion Nanoparticles

To solve the issue of limited penetration depth and overheating of the excited 980 nm near-infrared (NIR) light, and unstable and insufficient loading amount of photosensitizers (PSs) in photodynamic therapy (PDT), we have constructed a well-defined core–shell structured NaGdF4:Yb/Tm@NaGdF4:Yb@NaNdF4:Yb@NaGdF4@mSiO2@TiO2 (UCNPs@mSiO2@TiO2) nanocomposite by coating a layer of TiO2 PSs/photocatalyst on an effective 808 nm-to-UV/visible upconversion luminescent (UCL) core to achieve simultaneous multiple bioimaging and efficient PDT. The design of quenching-shield layer can eliminate the back energy transfer from activator Tm3+ to sensitized Nd3+, thus significantly improving the UCL emission. The high surface area of mesoporous silica-coated UCNPs facilitates the stable and high loading amount of anatase TiO2. In vivo results indicate that 808 nm NIR light-mediated PDT using UCNPs@mSiO2@TiO2 as photosensitizers shows much higher antitumor efficacy than those with 980 nm and UV irradiations due to the higher...

Red to UV and blue up-conversion in alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions via low energy pumping

This paper reports the up-conversion emission properties of alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions under 650 nm pumping using a low power xenon lamp source. Two UV emission bands which centered at 349 nm for the 1I6 → 3F4 transition of Tm3+ ion and at 367 nm for the 1D2 → 3H6 transition of Tm3+ ion and two blue emission bands which centered at 457 nm for the 1D2 → 3H4 transition of Tm3+ ion and at 485 nm for the 1G4 → 3H6 transition of Tm3+ ion have been observed. The up-conversion emission follows a two-photon absorption process for both blue bands, and the UV band centered at 367 nm but follows a cross-relaxation process for the UV band centered at 349 nm. The concentration quenching effect is relatively low in this material under 650 nm pumping. Due to the back energy transfer from Yb3+ to Tm3+ ions, the intensity of UV emission corresponding to the 1I6 → 3F4 transition of Tm3+ ion is stronger in alumina sol samples containing both Tm3+ and Yb3+ ions than in which containing only Tm3+ ions.

Energy transfer pathways among phycobilin chromophores and fluorescence emission spectra of the phycobilisome core at 293 and 77 K.

Energy transfer pathways between phycobiliproteins chromophores in the phycobilisome (PBS) core of the cyanobacterium Synechocystis sp. PCC 6803 were investigated. The computer 3D model of the PBS core with determination of chromophore to chromophore distance was created. Our kinetic equations based on this model allowed us to describe the relative intensities of the fluorescence emission of the short(peaked at 665 nm) and long-wavelength (peaked at 680 nm) chromophores in the PBS core at low and room temperatures. The difference of emissions of the PBS core at 77 and 293 K are due to the back energy transfer, which is observed at room temperature and is negligible at 77 K.

Broad and intense NIR luminescence from rare earth doped SiO2–Nb2O5 glass and glass ceramic prepared by a new sol gel route

A new sol–gel route was used for obtaining Er3+/Yb3+ co-doped Nb2O5 nanoparticles distributed in a SiO2 based host. Phase separation and crystallization process were investigated for Er3+/Yb3+ co-doped nanocomposites at 70Si:30Nb molar ratio. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier transform infrared (FTIR), Raman, and Photoluminescence (PL) spectroscopy were used to assess the structural properties and their influence on luminescence. Amorphous Nb2O5 was identified after nanocomposite annealing at 700°C, whereas at 900°C and 1100°C were identified both the orthorhombic and monoclinic phases. The average crystallite sizes were 6.6nm at 900°C and 16.4nm at 1100°C. Intense and broad NIR emission was observed for the nanocomposites annealed at 700 and 900°C due to an efficient energy transfer from Yb3+ to Er3+ ions. Intense emissions at 980nm and 1550nm were also observed due to energy transfer from the host to Yb3+ and Er3+ ions, respectively. Additionally, a less efficient back energy transfer from Er3+ to Yb3+ ions was observed. The emission intensity and bandwidth were dependent on the nature of Nb2O5 crystalline phase, indicating that rare-earth (RE) ions are mostly distributed into Nb2O5 nanoparticles. The 4I13/2 and 2F5/2 excited state lifetimes were also dependent on Nb2O5 crystalline phase with shorter values for monoclinic Nb2O5. The featured luminescent properties exhibited by the rare earth-doped Nb2O5 make the nanocomposite materials potential candidates in many photonic applications.

Conjugated Polyelectrolyte-Induced Self-Assembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complexes.

Water-soluble cationic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal-metal-to-ligand charge transfer (MMLCT) absorptions and triplet MMLCT ((3) MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non-conjugated polyelectrolytes, driven by Pt⋅⋅⋅Pt and π-π interactions among the complex molecules. Interestingly, the two-component ensemble formed by [Pt(bzimpy-Et){CCC6 H4 (CH2 NMe3 -4)}]Cl2 (1) with para-linked conjugated polyelectrolyte (CPE), PPE-SO3 (-) , shows significantly different photophysical properties from that of the ensemble formed by 1 with meta-linked CPE, mPPE-Ala. The helical conformation of mPPE-Ala allows the formation of strong mPPE-Ala-1 aggregates with Pt⋅⋅⋅Pt, electrostatic, and π-π interactions, as revealed by the large Stern-Volmer constant at low concentrations of 1. Together with the reasonably large Förster radius, large HOMO-LUMO gap and high triplet state energy of mPPE-Ala to minimize both photo-induced charge transfer (PCT) and Dexter triplet energy back-transfer (TEBT) quenching of the emission of 1, efficient Förster resonance energy transfer (FRET) from mPPE-Ala to aggregated 1 molecules and strong (3) MMLCT emission have been found, while the less strong PPE-SO3 (-) -1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of (3) MMLCT emission in the PPE-SO3 (-) -1 ensemble.

Effect of Mn2+ ions on the enhancement red upconversion emission and energy transfer of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics

The effects of Mn2+ ions on the enhancement red upconversion emission intensity of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics were investigated. The ratio I698nm/I478nm significantly increases about ten-fold with the increase of Mn2+ concentrations up to 4.0mol.%. The red upconversion emission of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics is greatly enhanced, due to constitution of the energy transfer bridge. The upconversion mechanism, the energy transfer and back energy transfer processes between the (1G4→3H6), (3F2→3H6) transitions of Tm3+ ions and the ∣2F7/2, 4T1〉→∣2F7/2, 6A1〉 transitions of Mn2+–Yb3+ dimer were discussed.

Disputed Mechanism for NIR-to-Red Upconversion Luminescence in NaYF4:Yb(3+),Er(3+).

The most commonly proposed mechanisms for NIR-to-red upconversion in the well-studied material β-NaYF4:Er(3+),Yb(3+) are evaluated in order to resolve inconsistencies that persist in the literature. Each of four possible mechanisms is evaluated in terms of the direct analysis of spectroscopic data. It is shown that there are no important mechanisms that involve the first excited state of Er(3+), (4)I13/2, as an intermediate state. A large body of evidence overwhelmingly supports the proposed mechanism of Anderson et al., which suggests an intimate connection between NIR-to-red and NIR-to-blue upconversion. Namely, both red and blue upconversion are produced primarily by a three-photon excitation process that proceeds through the green emitting state to a dense manifold of states, (4)G/(2)K, above the blue emitting state, (2)H9/2. Competing relaxation mechanisms out of (4)G/(2)K determine the relative amounts of blue and red upconversion produced. Multiphonon relaxation from (4)G/(2)K results in blue upconversion, whereas back energy transfer from Er(3+)((4)G/(2)K) to Yb(3+)((2)F7/2) results in red emission.

Luminescence and energy transfer processes in europium and terbium complexes with 2-substituted cycloalkanones and 1,10-phenanthroline derivatives

Abstract A series of solid lanthanide complexes with 2-substituted cycloalkanones (CA) of the composition Ln(CA)3·Phn and Ln(CA)3·Bpy (Ln = Eu, Tb, Gd) have been synthesized and investigated using luminescence spectroscopy. CA = 2-acetylcyclohexanone (AcCHex), 2-isobutyrylcyclohexanone, 2-acetylcyclopentanone, 2-acetylbutyrolactone, 2-benzoylcyclohexanone, 2-acetyltetralone; Phn = 1,10-phenanthroline (Phen), 4,7-dimethyl-phenanthroline, 3,4,7,8-tetramethyl-phenanthroline, 5-phenyl-phenanthroline, 4,7-diphenyl-phenanthroline; Bpy = 2,2′-bipyridine. Tris and tetrakis compounds Ln(CA)3·2H2O and LnNa(CA)4 were also synthesized. The composition, structure and photophysical properties of the lanthanide cycloalkanonates having oligomethylene chain in the ligand are close to peculiarities of β-diketonates without tethered chain. But the presence of this chain can cause a decrease in the energy of the lowest triplet state of the ligand. The Stark structure of the Eu3+ electronic states in the europium CA adducts with heterocyclic diimines corresponds to the distorted tetragonal anti-prismatic coordination geometry of the luminescence center. The lifetimes of 5D4 (Tb3+) and 5D0 (Eu3+) states at 77 K are 0.55–0.85 ms. The luminescence efficiencies of the lanthanide CA adducts at 77 K are comparable with them for known β-diketonates. The back energy transfer from the 5D4 (Tb3+) state to the lowest triplets of the ligands is the main cause for the decrease in the 5D4 lifetime and the Tb3+ luminescence efficiency at 295 K. In the Ln(AcCHex)3·Phn complexes the energy absorbed by the two ligands is transferred to the lowest triplet state of Phn and then to Ln3+ ion. In other Ln(CA)3·Phen compounds, the energy transfer to Ln3+ ion is carried out through the lowest triplet state of CA, which is located below the Phen triplet. The preliminary data on photochemical stability of the compounds were obtained.

Synthesis and up-conversion luminescence properties of Er3+/Yb3+ co-doped Sr2CeO4 phosphors

Er3+/Yb3+ co-doped Sr2CeO4 phosphors were synthesized using a high-energy ball milling method at 1100°C. The X-ray diffraction patterns confirmed their orthorhombic structure. The up-conversion emissions corresponding to 2H11/2→4I15/2, S3/2→4I15/2 and 4F9/2→4I15/2 transitions peaking at 526nm, 552nm and 669nm have been observed under 975nm excitation. With the help of a schematic energy level diagram the up-conversion mechanisms were discussed in detail. The excited state absorption and energy transfer process were discussed as possible up-conversion mechanisms. The energy back transfer (4S3/2+2F7/2→4I13/2+2F5/2) contribute the increased intensity ratio of red to green emission in Sr2CeO4:Er3+/Yb3+ samples. A decay curve analysis for the UC emission corresponding to the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions in the Er3+/Yb3+ co-doped Sr2CeO4 phosphors was performed. The CIE chromaticity coordinates of the Er3+/Yb3+ co-doped Sr2CeO4 phosphors were located in the green region. The results indicate that the material may be suitable for applications in the fields of color displays and light emitting devices.

Up-conversion luminescence of Er3 +/Yb3 + co-doped LiYF4 nanocrystals in sol–gel derived oxyfluoride glass-ceramics

Up-conversion properties of Yb3+/Er3+ co-doped LiYF4 nanocrystals embedded in a sol–gel derived oxyfluoride glass-ceramic have been studied by comparison to the corresponding polycrystalline sample. Under 980nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 samples show green ((2H11/2, 4S3/2)→4I15/2) and red (4F9/2→4I15/2) up-conversion luminescences explained by a two-photon processes. The tendency for the saturation of the red up-conversion luminescence band observed in the glass ceramic was ascribed to a back energy transfer process Er3+–Yb3+ and cross-relaxation processes caused by the high Yb3+ and Er3+ ions concentrations in the nanocrystals.

High efficiency yellow fluorescent organic light emitting diodes based on m-MTDATA/BPhen exciplex

High efficient yellow organic light emitting diodes (OLEDs) based on exciplex were reported. The exciplex was formed by 4, 4' ,4 ''-tris (3-methylphenyl (phenyl) amino)-triphenylamine (m-MTDATA) and 4, 7- diphenyl-1, 10-phenanthroline (BPhen). The resulting yellow OLEDs exhibited an external quantum efficiency of over 7%, which is attributed to the effective energy back transfer from exciplex triplet state to exciplex singlet state. The maximum power efficiency of 25 lm/W was achieved. Doping a yellow phosphor Ir(bt)2(acac) into m-MTDATA: BPhen blend, a high efficiency device was achieved with a turn-on voltage of 2.1 V, maximum power efficiency and external quantum efficiency of 86.1 lm/W and 20.7%, respectively.

Tidally-forced flow in a rotating, stratified, shoaling basin

Baroclinic flow of a rotating, stratified fluid in a parabolic basin is computed in response to barotropic tidal forcing using the nonlinear, non-hydrostatic, Boussinesq equations of motion. The tidal forcing is derived from an imposed, boundary-enhanced free-surface deflection that advances cyclonically around a central amphidrome. The tidal forcing perturbs a shallow pycnocline, sloshing it up and down over the shoaling bottom. Nonlinearities in the near-shore internal tide produce an azimuthally independent ‘set-up’ of the isopycnals that in turn drives an approximately geostrophically balanced, cyclonic, near-shore, sub-surface jet. The sub-surface cyclonic jet is an example of a slowly evolving, nearly balanced flow that is excited and maintained solely by forcing in the fast, super-inertial frequency band. Baroclinic instability of the nearly balanced jet and subsequent interactions between eddies produce a weak transfer of energy back into the inertia-gravity band as swirling motions with super-inertial vorticity stir the stratified fluid and spontaneously emit waves. The sub-surface cyclonic jet is similar in many ways to the poleward flows observed along eastern ocean boundaries, particularly the California Undercurrent. It is conjectured that such currents may be driven by the surface tide rather than by winds and/or along-shore pressure gradients.

Photophysical studies of highly luminescent europium(III) and terbium(III) complexes functionalized with amino and mercapto groups

This work proposes the replacement of coordinated-water molecules from the precursor complexes [Ln(aba)3(H2O)] and [Ln(tta)3(H2O)2], (Ln=Eu3+, Gd3+ or Tb3+, aba−=aminobenzoate, tta−=thenoyltrifluoroacetonate) by the ligands mercaptobenzoate (mba−), mercaptopropionate (mpa−), phenanthroline (phen), dimethylformamide (dmf) and acetoacetanilide (aaa−), leading to anionic or neutral amino (–NH2) or mercapto (–SH) functionalized-lantanides (III) complexes with reasonable emission quantum yields for potential application on fluorescence microscopy of biological moieties. The complexes photophysical properties were studied using luminescence spectroscopy and theoretical models to determine the transfer and back energy transfer rates and quantum yields, that were compared with experimental ones. The anionic complexes [Eu(tta)3(L)]− showed high quantum yield values and their sensitization efficiency are in the range of 39–81%. The overlay of the ground state geometries, obtained from the Sparkle/PM3 model, of the complexes [Eu(tta)3(aba)]−, [Eu(tta)3(mba)]− and [Eu(tta)3(mpa)]−, suggest similar coordination polyhedrons occupied by the europium(III). The highest transfer rates T→5D1,0 were obtained for the anionic complexes [Eu(tta)3(L)]− which might be a result of the low triplet level energies and RL values.

Importance of suppression of Yb(3+) de-excitation to upconversion enhancement in β-NaYF4: Yb(3+)/Er(3+)@β-NaYF4 sandwiched structure nanocrystals.

Nanosized Yb(3+) and Er(3+) co-doped β-NaYF4 cores coated with multiple β-NaYF4 shell layers were synthesized by a solvothermal process. X-ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the materials. The visible and near-infrared spectra as well as the decay curves were also measured. A 40-fold intensity increase for the green upconversion and a 34-fold intensity increase for the red upconversion were observed as the cores are coated with three shell layers. The origin of the upconversion enhancement was studied on the basis of photoluminescence spectra and decay times. Our results indicate that the upconversion enhancement in the sandwiched structure mainly originates from the suppression of de-excitation of Yb(3+) ions. We also explored the population of the Er(3+4)F9/2 level. The results reveal that energy transfer from the lower intermediate Er(3+4)I13/2 level is dominant for populating the Er(3+4)F9/2 level when the nanocrystal size is relatively small; however, with increasing nanocrystal size, the contribution of the green emitting Er(3+4)S3/2 level for populating the Er(3+4)F9/2 level, which mainly comes from the cross relaxation energy transfer from Er(3+) ions to Yb(3+) ions followed by energy back transfer within the same Er(3+)-Yb(3+) pair, becomes more and more important. Moreover, this mechanism takes place only in the nearest Er(3+)-Yb(3+) pairs. This population route is in good agreement with that in nanomaterials and bulk materials.

Combustion synthesis and up-conversion luminescence of La2O2S:Er3+,Yb3+ nanophosphors

La2O2S:Er3+,Yb3+ nanocrystalline up-converting phosphors were synthesized by a combustion method at low temperature, using ethanol as pre-ignition fuel and thioacetamide as sulfurizing agent and organic fuel. The phosphors were characterized by powder X-ray diffractometry, scanning electron microscopy, UV/Vis/NIR spectroscopy and fluorescence spectroscopy. Pure and well-crystallized La2O2S:Er3+,Yb3+ nanoparticles, of the order of 50–200nm, are obtained after a post-treatment in a H2S/N2 flow for 2h at 1000°C. The efficient energy transfer from Yb3+ to Er3+ results in a strong up-conversion upon excitation at 980nm. The emission spectra show the intense green emissions corresponding to the (2H11/2, 4S3/2)→4I15/2 transitions and a red emission corresponding to the 4F9/2→4I15/2 transition. Additionally, within the investigated co-doping concentrations, no significant concentration quenching effect and back energy transfer from Er3+ to Yb3+ were evidenced. This research highlights the influence of the sulfurization treatment on the purity/crystallinity/morphology of the nanocrystals and the luminescence efficiency.

Observation of efficient population of the red-emitting state from the green state by non-multiphonon relaxation in the Er3+–Yb3+ system

AbstractThe rare earth Er3+ and Yb3+ codoped system is the most attractive for showcasing energy transfer upconversion. This system can generate green and red emissions from Er3+ under infrared excitation of the sensitizer Yb3+. It is well known that the red-emitting state can be populated from the upper green-emitting state. The contribution of multiphonon relaxation to this population is generally considered important at low excitation densities. Here, we demonstrate for the first time the importance of a previously proposed but neglected mechanism described as a cross relaxation energy transfer from Er3+ to Yb3+, followed by an energy back transfer within the same Er3+–Yb3+ pair. A luminescence spectroscopy study of cubic Y2O3:Er3+, Yb3+ indicates that this mechanism can be more efficient than multiphonon relaxation, and it can even make a major contribution to the red upconversion. The study also revealed that the energy transfers involved in this mechanism take place only in the nearest Er3+–Yb3+ pairs, and thus, it is fast and efficient at low excitation densities. Our results enable a better understanding of upconversion processes and properties in the Er3+–Yb3+ system.

Phonon-assisted energy back transfer-induced multicolor upconversion emission of Gd2O3:Yb3+/Er3+ nanoparticles under near-infrared excitation

Manipulation of upconversion (UC) emission is of particular importance for multiplexed bioimaging. Here, we precisely manipulate the UC color output by utilizing the phonon-assisted energy back transfer (EBT) process in ultra-small (sub-10 nm) Gd2O3:Yb(3+)/Er(3+) UC nanoparticles (UCNPs). We synthesized the Gd2O3:Yb(3+)/Er(3+) UCNPs by adopting the laser ablation in liquid (LAL) technique. The synthesized Gd2O3:Yb(3+)/Er(3+) UCNPs are small spherical and monoclinic structures. Continuous color-tunable (from green to red) UC fluorescence emission is achieved by increasing the concentration of Yb(3+) ions from 0 to 15 mol%. A phonon-assisted energy back transfer (EBT) process from Er(3+) ((4)S3/2 → (4)I13/2) to nearby Yb(3+) ((2)F7/2 → (2)F5/2), which can significantly enhance red emission at 672 nm and decrease green emission, is responsible for the color-tunable UC emission by increasing the Yb(3+) concentration in Gd2O3:Yb(3+)/Er(3+) UC nanoparticles.

Lanthanide diphosphonates based on a V-shaped ligand: syntheses, structures, experimental and theoretical luminescence properties

One series of isostructural lanthanide phosphonates, namely [Ln2(H2L)3][(H2O)5] (H4L = (5-methyl-1,3-phenylene)bis(phosphonic acid); Ln = Eu (1), Gd (2), Tb (3), and Dy (4)), have been successfully synthesized from a V-shaped rigid ligand. Systematic characterizations using single-crystal and powder X-ray diffraction (XRD), thermogravimetric analyses (TGA), and photoluminescence spectroscopy were accomplished. It was found that these compounds all crystallize in the cubic I213 space group, showing three-dimensional framework structures. The frameworks are stable up to 350 °C and show their respective characteristic metal-centered emissions. The photoluminescence properties were also theoretically investigated by using a newly developed software program – LUMPAC. The energy transfer and back energy transfer rates were estimated, and the T1 → 5D1 and T1 → 5D0 channels were revealed to be the dominant pathways. The combination of experimental and theoretical studies on the photoluminescence properties substantially supports the understanding and design of highly luminescent inorganic–organic hybrid materials.

Triplet states and energy back transfer of carbazole derivatives

The red-shift of triplet energies between the dilute phase and solid states is a function of intermolecular distance.

Scintillator-Oriented Investigation of Y3Al5O12:Ce,Tb Powders

The spectral and kinetic characteristics of YAG:Ce,Tb powders (with Tb3+ concentration varying up to 100%, relative to Y) using cathode-ray and UV excitations were determined. The energy diagram of YAG:Ce,Tb was constructed and energy transfer processes in the compound were studied. The most effective resonance energy transfer takes place at Tb3+ concentrations of 20%. There is no evidence of Ce3+→Tb3+ energy back transfer for (Y,Tb)AG:Ce even in high resolution spectra. The optimal Tb3+ content for maximum light output of YAG:Ce,Tb was determined to be 20% and for lowest afterglow 100%.