Two-photon Energy Transfer Research Articles

Correlation between local lattice distortions and up-/down-conversion luminescence of (Y,Al)NbO4:Yb3+/Er3+

The changes in the crystallographic parameters of Y 0.79- z Al z Yb 0.18 Er 0.03 NbO 4 powders prepared with varying Al content were determined by Rietveld refinement, and their effects on the up- (UC) and down-conversion (DC) spectra were studied. The findings confirmed that the Al 3+ , Yb 3+ , and Er 3+ ions were completely incorporated at the Y 3+ sites. The substitution of the small Al 3+ ions led to the modification of the interatomic distance. As a result, the highest polyhedral distortion index of the YO8 dodecahedron ( D YO ) could be achieved at z = 0.2. Under infrared radiation, UC spectra demonstrated that a two-photon energy transfer (ET) UC process from Yb 3+ to Er 3+ was responsible for the green and red emissions, whose intensities increased dramatically by 160 and 166% at z = 0.2, respectively. This enhancement was a consequence of a large crystal-field asymmetry surrounding the Yb 3+ and Er 3+ ions, which resulted from the highest D YO at z = 0.2. In addition to D , the Yb‒Er interatomic distance was responsible for the enhanced UC emission, affecting the ET probability from Yb 3+ to Er 3+ . Under 379 nm excitation, the DC green emission of Er 3+ also showed the maximal intensity at z = 0.2 owing to the largest D YO . However, a correlation between the crystallographic variations and the DC emissions activated by [NbO 4 ] 3- niobates could not be fully elucidated owing to the complexity of the emission mechanism.

Tunable structure and intensive upconversion photoluminescence for Ho3+-Yb3+ codoped bismuth titanate composite synthesized by sol-gel-combustion (SGC) method

Ho3+ and Yb3+ codoped bismuth titanate (BTO) composite powders with infrared to visible upconversion luminescence (UCL) function were prepared by SGC method. The effects of Ho3+ and Yb3+ doping content on the structure and property were investigated for BTO: xHo, 0.2 Yb (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) and BTO: 0.02Ho, yYb (y = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) samples. All the samples include three bismuth titanate phases (Bi4Ti3O12, Bi2Ti2O7, and Bi20TiO32), and the phase proportion can be tuned by changing Ho3+ and Yb3+ doping content. These powders are well crystalized with honeycomb-like microscopic structure, and with good absorption for 233 nm, 310 nm and 975 nm wavelength. The band gap can be tuned from 3.53 eV to 4.03 eV when increasing Yb3+ content from y = 0 to y = 0.9. A strong 530–580 nm green emission band and a relative weak 630–690 nm red one corresponding to Ho3+: 5S2 → 5I8 and 5F5 → 5I8 transitions appear in the UCL spectra for all the BTO: Ho, Yb samples when pumped at 980 nm. The emission intensities can well be tuned with various Ho3+ and Yb3+ content. The optimal UCL was obtained in BTO: 0.02Ho, 0.5 Yb for all the prepared samples. The energy transfer mechanism is analyzed by building a two-photon energy transfer model, which is proved by the relationship between emission intensities and pumping power measurement. The concentration quenching of Ho3+ is caused by cross relaxation of CR1 and CR2 (Ho: 5F4, 5S2 + 5I8 → 5I4 + 5I7) and by CR3 (Ho: 5F4, 5S2 + Yb: 2F7/2 → Ho: 5I6 + Yb: 2F5/2) for Yb3+ quenching. The mean luminescence lifetime (τm) from Ho: 5S2 decreases monotonously with the increase of Ho3+ and Yb3+ content.

Visualizing Endogenous Sulfur Dioxide Derivatives in Febrile-Seizure-Induced Hippocampal Damage by a Two-Photon Energy Transfer Cassette.

Febrile seizure (FS), a frequently encountered seizure disorder in pediatric populations, can cause hippocampus damage. It has been elucidated that sulfur dioxide (SO2) content is overproduced during the development of FS and related brain injury. Thus, monitoring in situ the level of endogenous SO2 in FS-related models is helpful to estimate the pathogenesis of FS-induced brain injury, but the effect detection method remains to be explored. Herein, we developed a two-photon energy transfer cassette based on an acedan-anthocyanidin scaffold, TP-Ratio-SO2, allowing us to achieve this purpose. TP-Ratio-SO2 specifically responds to SO2 derivatives (HSO3-/SO32-) in an ultrafast fashion (less than 3 s), and HSO3-/SO32- can be sensitively determined with a detection limit of 26 nM. Moreover, it exhibits significant changes in two well-resolved fluorescence emissions (Δλ = 140 nm) by reacting with HSO3-/SO32-, behaving as a ratiometric fluorescent sensor. Importantly, ratiometric imaging of endogenous SO2 derivatives generation in hyperpyretic U251 cells and in a rat model of FS-treated hippocampus damage was successfully carried out by TP-Ratio-SO2, demonstrating that it may be a promising tool for studying the role of SO2 in FS-associated neurological diseases.

Ratiometric Visualization of NO/H2S Cross-Talk in Living Cells and Tissues Using a Nitroxyl-Responsive Two-Photon Fluorescence Probe.

It is of scientific significance to explore the intricate relationship between two crucial gasotransmitters nitric oxide (NO) and hydrogen sulfide (H2S) because they exert similar and interdependent biological actions within the living organisms. Nevertheless, visualization of the NO/H2S crosstalk using effective molecular imaging tools remains challenging. To address this issue, and given that nitroxyl (HNO) has been implicated as the interdependent production of NO and H2S via a network of cascading chemical reactions, we herein design a ratiometric two-photon fluorescent probe for HNO, termed TP-Rho-HNO, which consists of benzo[h]chromene-rhodol scaffold as two-photon energy transfer cassette with phosphine moiety as specific HNO recognition unit. The newly proposed probe has been successfully applied in ratiometric two-photon bioimaging of endogenous HNO derived from NO and H2S interaction in the human umbilical vein cells (HUVECs) and as well as in rat brain tissues. Intriguingly, the imaging results consistently demonstrate that the mutually dependent upgeneration of H2S and NO are present in living biosystems, indicating that this molecular probe would provide a powerful approach to elucidate the chemical foundation for the anfractuous cross-talk between the NO and H2S signaling pathways in biology.

Designing Upconversion Nanocrystals Capable of 745 nm Sensitization and 803 nm Emission for Deep-Tissue Imaging.

A crystal design strategy is described that generates hexagonal-phased NaYF4 :Nd/Yb@NaYF4 :Yb/Tm luminescent nanocrystals with the ability to emit light at 803 nm when illuminated at 745 nm. This is accomplished by taking advantage of the large absorption cross-section of Nd(3+) between 720 and 760 nm plus efficient spatial energy transfer and migration through Nd(3+) →Yb(3+) →Yb(3+) →Tm(3+) . Mechanistic investigations suggest that a cascaded two-photon energy transfer upconversion process underlies the emission mechanism. This protocol enables deep-tissue imaging to be achieved while mitigating the attenuation effect associated with the visible emission and the overheating constraint imposed by conventional 980 nm excitation.

Nonlinear energy transfer in quantum dot and metallic nanorod nanocomposites

We have investigated the nonlinear energy transfer in a quantum dot (QD) and metallic nanorod (MNR) nanocomposite. An intense probe laser field is applied to monitor two-photon energy transfer from the QD to the MNR and a control laser field is applied to control the energy transfer rate. Induced dipoles are created in the QD and MNR and these dipoles are interacting with each other. Surface plasmon resonances (SPRs) are also created in the MNR due to a coupling of charge fluctuations and external laser fields. Therefore, there is a dipole–dipole interaction between excitons in the QD and SPRs in the MNR. Due to this interaction, the two-photon energy is transferred from the QD to the MNR. Using the density matrix method, the energy transfer rate between the components of the system is evaluated. It is found that the energy transfer rate has one peak due to the transfer of the two-photon energy from the QD to the MNR when the control field is absent. When the control field is applied, this peak disappears. This means no energy transfer between two components of the nanosystems. However, two new peaks appear in the energy transfer rate at two different energies. It is also found that by varying the intensity of the probe field, one can also control the energy transfer from the QD to the MNR. These are interesting findings of the paper and they can be used to fabricate nanosensors, nanoswitches, and energy transfer devices.

Structure, upconversion photoluminescence, and dielectric properties of Ho3+- and Yb3+-codoped tetragonal tungsten bronze Sr4La2Ti4Nb6O30

Ho3+- and Yb3+-codoped Sr4La2Ti4Nb6O30 (Sr4La1.94–xHo0.06YbxTi4Nb6O30, abbreviated as SLTN: Ho-Ybx) ceramics have been synthesized, and their structural, up-conversion (UC) photoluminescence, and dielectric properties have been carefully investigated. Through Rietveld structural refinement, SLTN: Ho-Ybx samples are determined as single tetragonal tungsten bronze (TTB) phase with space group P4/mbm in which larger Sr2+ ions fill the A2-sites, relative smaller La3+, Ho3+, and Yb3+ ions occupy the A1-sites, while Ti4+ and Nb4+ ions fill the B-sites. Under 980nm near infrared (NIR) excitation, bright UC green emission, relatively weak red and near-infrared (NIR) emissions, originating from 5F4/5S2→5I8, 5F5→5I8, and 5F4/5S2→5I7 transitions of Ho3+ ions, are confirmed for SLTN: Ho-Ybx. Two-photon energy transfer process is proved through pumping laser power dependence of emission intensity measurement. Furthermore, the influence of Ho3+- and Yb3+- ions on the dielectric properties of SLTN: Ho-Ybx is also investigated and the temperature stability of dielectric permittivity is improved.

Upconversion photoluminescence and dielectric properties in Er3+ and Yb3+ co-doped Sr4La2Ti4Nb6O30

Filled tetragonal tungsten bronze (TTB) structure Sr4La2Ti4Nb6O30 co-doped by Er3+ and Yb3+ (SLTN: xEr3+–yYb3+) ceramics with different x and y were synthesized, and their crystal structure, upconversion photoluminescence (UC-PL), and dielectric permittivity were investigated for the first time. Under 980nm infrared (IR) excitation, bright single-band UC green (515–570nm) emission was observed for SLTN: xEr3+–yYb3+ (x=0.05, y=0), however, featured two-bands UC emission (515–570nm and 640–690nm) was confirmed for all SLTN: xEr3+–yYb3+ (x=0.05, y≠0) samples. Two-photon energy transfer process was proved through pumping laser power dependence of emission intensity measurement. It is believed that energy back transfer (EBT) process should be mainly responsible for the two-bands UC emission. In addition, the dielectric properties were also discussed for SLTN: xEr3+–yYb3+ system.

Bright green upconversion emission and enhanced ferroelectric polarization in Sr1−1.5xErxBi2Nb2O9

Upconversion (UC) luminescence and ferroelectric (FE) polarization properties were first investigated in polycrystalline Er3+-doped SrBi2Nb2O9 (SBN:xEr3+) samples. Bright UC green and weak UC red emission, originating from (2H11/2, 4S3/2)–4I15/2 and 4F9/2–4I15/2 transitions, respectively, was confirmed to be a two-photon energy transfer process. The UC green luminescence can be seen by the naked eye at room temperature. The optimal UC green emission was obtained when x=5mol.% in SBN:xEr3+. Furthermore, it is surprisingly found that a proper Er3+ doping can also remarkably enhance the FE polarization of SBN:xEr3+.

Tm3+浓度对Y2(MoO4)3∶Tm3+,Yb3+荧光粉上转换发光性质的影响

采用传统的高温固相反应法合成了Tm3+/Yb3+共掺杂Y2(MoO4)3系列荧光粉。XRD结果表明合成的样品为相纯度好的Y2(MoO4)3。在980 nm光激发下,样品具有较强的位于487 nm和800 nm的蓝色和近红外发射,同时伴有较弱的位于649 nm的红光发射。它们分别来自于Tm3+的1G4→3H6、3H4→3H16和G4→3F4跃迁。根据功率相关的上转换发射和能级图分析了Tm3+的上转换发光机制。结果表明,1G4和3H4能级的布居分别来自于三光子和两光子的能量传递上转换。此外,随着Tm3+浓度的增加,蓝色、红色和近红外发射带均呈先增加后降低的趋势,即发生了浓度猝灭。同时,蓝光发射和近红外发射的强度比随Tm3+掺杂浓度的增加而减小。

Upconversion luminescence and ferroelectric properties of Er3+ doped Bi4Ti3O12–SrBi4Ti4O15

Er3+ doped intergrowth Bi4Ti3O12–SrBi4Ti4O15 (BIT–SBTi: xEr3+) ceramics have been synthesized by a solid state processing. Upconversion (UC) luminescence and ferroelectric (FE) polarization properties were first investigated. Bright UC green emission, originating from (2H11/2,4S3/2)–4I15/2 transitions, was confirmed to be a two-photon energy transfer process by pumping laser power dependence of emission intensity. The UC green luminescence can be seen by the naked eye at room temperature. Furthermore, it is found that a proper Er3+ doping can also remarkably enhance the FE polarization of BIT–SBTi: xEr3+. The results indicated that BIT–SBTi: xEr3+ with good UC emission and high FE polarization can act as a potentially multifunctional optical-electro-material.

Structural and Luminescence Properties of Ho<SUP>3+</SUP>/Yb<SUP>3+</SUP>-Doped Lu3Ga5O12 Nano-Garnets for Phosphor Applications

Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a citrate sol-gel technique. The structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The materials are found to exist in single phase of cubic garnet structure with an average particle size of around 45 nm. The Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnet powders give rise to an intense green and weak red emission of Ho3+ ions under 457.5 nm direct excitation. Moreover, when the Yb3+ ions are excited at 950 nm a very bright green luminescence of the Ho3+ ions is observed by the naked eyes even for such low laser power as 10 mW and the intensity of the red emission have been increased compared to that found under direct excitation of the Ho3+ ions. The power dependency and dynamics of the infrared-to-visible upconverted luminescence confirm the existence of different two-photon energy transfer processes. All these results have been compared with those obtained for other garnets doped with similar lanthanide ions which suggest that the Lu3Ga5O12 nano-garnets are potential materials for light emitting devices.

Light harvesting in dendrimer materials: Designer photophysics and electrodynamics

Abstract

Upconversion Luminescence Properties of YF3:Yb3+, Er3+ Nanoclusters

The synthesis, characterization, and spectroscopy of upconverting Yb3+/Er3+ codoped YF3 rod-like nanoclusters are presented. The YF3 nanoclusters were synthesized by a simple hydrothermal method. The clusters structure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Under 978 nm laser excitation, stronger blue (4F(5/2) --> 4I(15/2) and 2p(3/2) --> 4I(11/2)) and green (4S(3/2), 2H(11/2) --> 4I(15/2)) upconversion luminescence were observed at 978 nm. The measured intensity of upconversion luminescence was different when pump power changed, which shows that the blue and green upconversion luminescence come from three-photon and two-photon energy transfer processes, respectively.

Structural and optical investigation of colloidal Ln3+/Yb3+ co-doped KY3F10 nanocrystals

We report for the first time the synthesis of colloidal Ln3+/Yb3+ co-doped KY3F10nanocrystals (Ln = Er or Eu) viathermal decomposition. The transmission electron microscopy (TEM) studies indicated that the average size of the nanocrystals was approximately 15 nm. The nanocrystals crystallized in the cubic Fmm space group as confirmed by Rietveld refinement of the X-ray powder diffraction patterns and by electron diffraction analysis. The Eu3+ ion was used as a spectroscopic probe and its emission spectrum in colloidal KY3F10nanocrystals showed that the lanthanide ions replaces Y3+ in the lattice structure. When co-doped with Er3+/Yb3+, colloidal KY3F10nanocrystals exhibited visible (green and red) upconversion emissions following 978 nm excitation with a near-infrared (NIR) diode laser. Power dependence studies indicated that a two-photon energy transfer upconversion process was responsible for the NIR-to-visible upconversion.

Two-photon energy transfer enhanced three-dimensional optical memory in quantum-dot and azo-dye doped polymers

A three-dimensional bit-by-bit optical memory system in quantum-dot and azo-dye doped polymers is demonstrated in this paper. It is shown that two-photon absorption can be used to excite resonance energy transfer from luminescent CdS quantum dots to azo-dye molecules. As a result, the isomerization of azo-dye molecules leads to a pronounced refractive index change. This two-photon-excited energy transfer process in the quantum-dot and azo-dye polymer not only allows for high efficient multilayer information recording into the volume of thick samples but also offers a refractive index window for readout.

Synthesis of C60-diphenylaminofluorene dyad with large 2PA cross-sections and efficient intramolecular two-photon energy transfer.

The first, highly two-photon active C60 derivative comprised of a A-sp3-D conjugate structure was synthesized showing effective two-photon absorption cross-sections (sigma 2' = 196 x 10(-48) cm4 sec-1 molecule-1) in the nanosecond regime among the best values for diphenylaminofluorene-based AFX chromophores.