The Luminescence Properties and Intramolecular Energy Transfer of Rare Earth Complexes with Aromatic Carboxylic Acids

The triplet state energies of para aminobenzoic acid and nicotinic acid were determined by means of low temperature phosphorescence spectrometry. The energy matches between them and the resonant emitting energy levels of Eu 3+ , Tb 3+ , Sm 3+ , Dy 3+ were studied. The intramolecular energy transfer processes from the two aromatic carboxylic acid ligands to rare earth ions were also discussed on the basis of the measurement results of luminescence intensities, lifetimes and quantum efficiencies.

Studies on Intermolecular Energy Transfer and Relaxation Processes in Solid Rare Earth Complexes by Photoacoustic Spectroscopy

The photoacoustic spectra of Eu ( benz)(3) (.) ( phen)(2) ( benz: benzoate, phen: phenanthroline) and Eu-0.(8)Ln(0.2)(benz)(3)(.)(phen)(2)(Ln(3+) : La3+ or Nd3+) were reported. The intermolecular energy transfer processes were studied from the point of the nonradiative transitions. Combined with the fluorescence spectroscopy, photoacoustic spectroscopy reflects the variation of the luminescence efficiencies of solid samples. The luminescence efficiency increases when La3+ is introduced, but it decreases greatly when Nd3+ is added, which is due to the difference of intermolecular energy transfer processes. The models of intramolecular and intermolecular energy transfer and relaxation processes were established.

Improved anti-Stokes energy transfer between rare earth ions in Er(0.5)Yb(9.5):FOV oxyfluoride vitroceramics explains the strong color reversal

The widely used energy transfer theory is a foundation of luminescence, in which the rates of Stokes and anti-Stokes processes have the same calculation formula. An improvement on the anti-Stokes energy transfer to explain the fluorescence intensity reversal between the red and green fluorescence of Er（0.5）Yb（9.5）：FOV is reported in the present article. The range of the intensity reversal Z was measured to be 877. Dynamic processes for 16 levels were simulated. A coefficient, the improvement factor of the intensity ratio of Stokes to anti-Stokes processes in quantum Raman theory compared to classical Raman theory, is introduced to successfully describe the anti-Stokes energy transfer. A new method to calculate the distance between the rare earth ions, which is critical for the energy transfer calculation, is proposed. The validity of these important improvements is also proved by experiment.

Study on Spectral Overlap Model for Energy Transfer between J-Multiplets in Rare Earth-Doped Crystals

Based on the experimental data of KY 3F 10∶Tm 3+ reported by Diaf, K ushida′s spectral overlap model (SOM) of energy transfer between J-multipl ets was studied. Firstly, with the help of the Inokuti-Hirayama and Yokota-Tan imoto models, the luminescence decay curve of 3H 4 of Tm 3+ ion was fitted, and the fitted values of corresponding interaction parameters C D A of energy transfer and C DD of energy migration were obtained. Seco ndly, by compared with Kushida′s SOM in which the relevant Judd-Ofelt approxim ative transition rates are known, the average overlap integrals of S DD and S DA were obtained. For S DD, how to treat the contributi on of the electronic-dipole (ED) crystal field transition forbidden by C 4v site symmetry in the calculation of S DD was discussed. For S DA we suggested that, by including the contribution of the phonon sideba nds in the analysis of oscillator strength of transition, Kushida′s SOM of ED- ED resonant energy transfer rate can be extended to non-resonant phonon-assist ed D-A energy transfer. The strengths and widths of phonon sidebands in this ex ample were discussed, and the results were reasonably good.

Multiple Energy Transfers in Rare Earth Complex-Doped SiO_2 Spheres

Silica spheres doped with Eu （TTFA）3 and/or Sm（TTFA）3 were synthesized by using the modified Stober method. The transmission electron microscope image reveals that the hybrid spheres have smooth surfaces and an average diameter of about 210 nm. Fluorescence spectrometer was used to analyze the fluorescence properties of hybrid spheres. The results show that multiple energy transfer processes are simultaneously achieved in the same samples co-doped with Eu （TTFA）3 and Sm（TTFA）3, namely between the ligand and Eu^3＋ ion, the ligand and Sm^3＋ ion, and Sm^3＋ ion and Eu^3＋ ion. Energy transfer of Sm^3＋→Eu^3＋ in the hybrid spheres leads to fluorescence enhancement of Eu^3＋ emission by approximately an order of magnitude. The lifetimes of the hybrid spheres were also measured.

A Theoretical Model of Energy Transfer between Rare Earth Ions in Crystals

The limitation of the random walk theory of energy transfer between rare earth ions in crystals published in literatures is pointed out in this paper. A modified model, which can be used in any level of rare earth ion concentration when the interaction between donor and acceptor is different from that between donors, is introduced. measured fluorescence lifetimes of Yb^3＋：YAl3（BO3）4 This model has been applied to analyze the with a series of Yb^3＋ concentrations.

Sensitization and Intra-molecular Energy Transfer of Eu^(3+) by Tb^(3+) in Eu-Tb Binuclear Complexes/PMMA

A series of Eu0.5Tb0.5（TTA）3Phen/PMMA （TTA=thenoyltrifluoroacetone,Phen=phenanthroline） and Eu0.5Tb0.5（TTA）3Dipy/PMMA （Dipy=2,2’-dipyridyl） were prepared by in-situ polymerization.The structures of the composites were characterized by IR spectra and electron spectrum.Photoluminescence properties were investigated by UV-Vis spectra and fluorescence spectra.Meanwhile,the energy transfer models were set up.The results indicated that polymer parts were attached with the rare-earth molecular parts in the composite luminescent materials.Eu0.5Tb0.5（TTA）3Phen/PMMA and Eu0.5Tb0.5（TTA）3Dipy/PMMA emitted mostly characteristic fluorescence of europium ion and intense red fluorescence with peak wavelength at 611.8 nm and bandwidth of 10.4 nm under UV excitation at 365 nm.Fluorescence intensity of Eu0.5Tb0.5（TTA）3Phen/PMMA was found to be influenced with the content of MMA.The fluorescence emission of europium ions was greatly sensitized by terbium ions and the enhancement of red emission was most likely due to the energy transfer enhancement from Tb3＋ to Eu3＋.

Effects of CeCl_3 on Energy Transfer and Oxygen Evolution in Spinach Photosystem Ⅱ

Due to 4f electron characteristics and alternation valence, cerium involved in an oxidation-reduction reaction in plant, closely relating to photosynthesis. Our studies proved that cerium could promote photosynthesis and greatly improve spinach growth. However, the mechanism of promoting energy transfer and conversion by cerium remains unclear. Here we reported that the effects of Ce^3＋ on energy transfer and oxygen evolution in photosystem Ⅱ （PS Ⅱ ） isolated from spinach, which was related to 4f electron characteristics and alternation valence in Ce molecule. The methods of absorption spectrum, fluorescence spectrum were used in the research. Results showed that Ce^3＋ treatment at low concentration could suitably change PS Ⅱ mieroenvironment, increase the absorbance of visible light, improve the energy transfer among amino acids within PS Ⅱ protein-pigment complex, and accelerate energy transport from tyrosine residue to chlorophyll a. In summary, the photochemical activity of PS Ⅱ （fluorescence quantum yield） and its oxygen evolving rate were enhanced by Ce^3＋.

Luminescence and Energy Transfer Properties of Ca_2Gd_8(SiO_4)_6O_2∶A(A=Pb^(2+), Tm^(3+))Phosphors

Ca_2Gd_8(SiO_4)_6O_2∶ A(A=Pb^(2+), Tm^(3+))phosphors were prepared through the sol-gel process. X-ray diffraction(XRD), scanning electron microscopy(SEM)and photoluminescence spectra were used to characterize the resulting phosphors. The results of XRD indicate that the phosphors crystallized completely at 1000 ℃. SEM study reveals that the average grain size is 300～1000 nm. In Ca_2Gd_8(SiO_4)_6O_2∶Tm^(3+) phosphors, the Tm^(3+) shows its characteristic blue emission at 456 nm(~1D_2—~3F_4)upon excitation into its ~3H_6—^(1)D_2(361 nm), with an optimum doping concentration of 1mol% of Gd^(3+) in the host lattices. In Ca_2Gd_8(SiO_4)_6O_2∶Pb^(2+), Tm^(3+) phosphors, excitation into the Pb^(2+) at 266 nm(~1S_0—~3P_1)yields the emissions of Gd^(3+) at 311 nm(~6P—~8S)and Tm^(3+) at 367 nm(~1D_2 —~3H_6)and 456 nm(~1D_2—~3F_4), indicating that energy transfer processes of Pb^(2+)—Gd^(3+) and Pb^(2+)—Tm^(3+) have occurred in the host lattices.

Spectral properties and energy transfer of Tm^(3+)/Ho^(3+)-codoped Ga_2O_3-Bi_2O_3-GeO_2-PbO glasses

The 2.0 μm emission originating from Ho^3＋：^5I7→^5I8 were investigated upon excitation with 808 nm laser diode （LD） transition in Ho^3＋/Tm^3＋-codoped gallate-bismuth-germanium-lead glasses Energy transfer （ET） process between Tm^3＋： ^3F4 level and Ho^3＋： ^5I7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho^3＋-doped bismuth-germanium-lead glasses were -2.02 μm and 5.1×10^-21 cm^2, respectively. Intense emission of Ho^3＋ in Tm^3＋/Ho^3＋-codoped GBPG glass were observed, which resulted from the ET between Tm^3＋： ^3F4 and Ho^3＋： ^5I7 level upon excitation with 808 nm LD.

Investigation on energy transfer from Er^(3+) to Nd^(3+) in tellurite glass

A study of energy transfer of Er^3＋/Nd^3＋ codoped tellurite glasses was presented. By Nd^3＋ co-doping, both the Er^3＋ green emission corresponding to the Er^3＋： （^4S3/2, ^2H11/2）→^4I15/2 transitions and the red emission corresponding to the Er^3＋： ^4F9/2→^4I15/2 transitions were quenched. The energy transfer mechanism between Er^3＋ and Nd^3＋ was discussed based on their energy level characteristics. The interaction parameters, CO-A, for the energy transfer processes from Er^3＋ to Nd^3＋ in tellurites glass were calculated. Finally, the resonant transfer Er^3＋： ^4I9/2→Nd^3＋： （^4F5/2, ^2H9/2） was proposed to be the most probable microscopic process to occur in contrast with the other processes.

Photon Cascade Emission through Energy Transfer in Pr^(3+) and Er^(3+) Codoped System

Energy transfer processes in Pr 3+ and Er 3+-codoped CaAl 12O 19 crystal from 12 to 290 K were studied. Energy transfer from Pr 3+ to Er 3+ ions in this system was observed. The transfer can partially convert the 1S 0 UV fluorescence of Pr 3+ into green emission of the characteristic of Er 3+. The efficiency of the energy transfer was estimated based of the spectroscopic data. The temperature dependence on the transfer was also discussed.

Tunable Emission and Energy Transfer of the Novel KY_(1-x)(MoO_(4))_(2-y)(WO_(4))y:xLn^(3+)(Ln^(3+)=Dy^(3+),Eu^(3+),and Tm^(3+))Single-phase White Luminescence Phosphor for White LEDs

The phosphors of KY_(1-x)(MoO_(4))_(2-y)(WO_(4))y:xLn^(3+)(Ln^(3+)=Tm^(3+),Dy^(3+),Eu^(3+))were synthesized by using a sol-gel method.Then,the crystal structure,luminescence properties,energy transfer,and white emission of the prepared materials were researched.The molar ratio of the anion group on the photoluminescence(PL)emission and excitation intensity were investigated,revealing that the optimum intensity could be obtained by using=3:1.The optimal Dy^(3+) doping concentration of KY(MoO_(4))1.5(WO4)0.5was obtained.In addition,the color-tunable emissions of Dy^(3+)/Eu^(3+)-codoped KY(MoO_(4))1.5(WO4)0.5phosphors were observed because of the effective energy transfer(ET)from Dy^(3+)to Eu^(3+)ions.Finally,by doping appropriate concentrations of Tm^(3+),Dy^(3+),and Eu^(3+)and different concentrations of(WO_(4))^(2-),white light emitting phosphors KY_(0.92)(WO_(4))2:0.01Tm^(3+),0.06Dy^(3+),0.01Eu^(3+)with excellent color-rending properties were obtained.The chromaticity coordinate was calculated as(x=0.3238,y=0.3173),closing to the artificial daylight(D65,x=0.313,y=0.329)illuminant,and which indicates the potential application of near ultraviolet White light-emitting diodes(WLEDs).

Photoluminescence and Energy Transfer Process in Bi³⁺/Sm³⁺Co-Doped Phosphate Zinc Lithium Glasses

Present paper reports on luminescence characteristics of individually doped Bi3+: PZL, Sm3+: PZL and co-doped (Bi3+/Sm3+): PZL (50P2O5-30ZnO-20LiF) glasses prepared by a melt quenching method. The results revealed that Bi3+: PZL glass exhibited a broad emission peak at 440 nm (3P1→1S0) under excitation wavelength 300 nm (1S0→3P1). Sm3+: PZL doped glass has shown a prominent orange emission at 601 nm (4G5/2→6H7/2) with an excitation wavelength 403 nm (6H5/2→4F7/2). Later on Bi3+ is added to Sm3+: PZL glass by increasing its concentrations from 0.1 - 1.5 mol%. By co-doping Bi3+ to Sm3+: PZL glass, Sm3+ emission intensity has been considerably enhanced till 1.0 mol% due to energy transfer from Bi3+ to Sm3+ and when its concentration exceeds this critical value (1.0 mol%) there has been a drastic decrease in Sm3+ emission which is explained accordingly from photoluminescence spectra, energy level diagram and lifetime measurements.

Site Selective Excitation and Energy Transfer in LiKGdF_5 Crystal Co-doped with Er^(3+) and Tb (3+)

Crystals of LiKGdF 5∶Er 3+, Tb 3+ grown by the hydrothermal synthesis technique with concentrations of 2% and 0.4% were analysed. By using site selective excitation measured at low temperature, luminescence and excitation spectra from Er 3+ and Tb 3+ ions embedded in LiKGdF 5 were clearly separated. The lifetimes of the emitting levels 4S 3/2 of Er 3+ and 5D 4 of Tb 3+ were also determined. Following the site selective spectroscopy study, the dominant energy transfer process from Tb 3+ to Er 3+ in the crystal was then investigated via transient experiments.

Rare earth upconversion nanophosphors: synthesis, functionalization and application as biolabels and energy transfer donors

This review focused on rare earth upconversion nanophosphors (UCNPs), a particular class of emitters whose photoluminescence mechanism is of fundamental difference from that of conventional dyes and semiconductor quantum dots. We in the first section gave a brief summary on a variety of synthetic methodologies developed during the past decades. Instead of presenting an exhaustive reference list, we selected only a few representative examples, illustrating the merits and limits of each involved synthetic route. Then we surveyed the recent progress in the functionalization techniques for these nanomaterials, depicting the modification in microstructures and improvement in properties with respect to the parent nanoparticles. And finally, we emphasized their application in the research fields of biolabeling and energy transfer, narrating their superior performance benefiting from the unique excitation and emission properties.

Synthesis, luminescence properties and energy transfer of binary and ternary rare earth complexes with aromatic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with ortho hydroxyl benzoic acid, pam aminobenzoic acid, nicotinic acid and 1,10-phenanthroline were synthesized. Phosphorescence spectra and lifetimes of Gd complexes were measured and the lowest triplet state energies of gadolinium binary complexes end the intramolecular energy transfer efficiencies were determined. The luminescence properties and energy transfer process of Eu3+ and Tb3+ complexes were discussed.

Interparticle energy transfer between NaNdF_(4) and NaYbF_(4) in self-assembled nanostructures

Forster resonance energy transfer(FRET)is a widely used spectroscopic technique.The development of donor-acceptor combinations is essential to advance this technique.To make the energy transfer efficiency independent of the external environment,we explored the potential of constructing donor—acceptor combinations with lanthanide ion-doped nanoparticles(LNPs),in which the 4f electrons of the lanthanide ions are shielded by the 5s and 6p electrons.Non-radiative energy transfer between LNPs was demonstrated in self-assembled nanostructures and core-shell structure of LNPs was used to control the distance between donor and acceptor in self-assembled nanostructures.The emission intensity ratio of donor and acceptor illustrates that the energy transfer efficiency decreases significantly with increasing distance and the effective energy transfer distance is 8.5 nm,showing the potential of using LNPs as donor-acceptor pairs in the construction of distance-dependent energy transfer system.

Preparation,optical properties and energy transfer of SrLaAlO_(4):Dy^(3+),Eu^(3+)

A series of Dy^(3+)/Eu^(3+) single doped and co-doped SrLaAlO_(4) phosphors was synthesized by the traditional high-temperature solid-state method,and their structure,morphology and optical properties were characterized.The X-ray diffraction(XRD) shows a small amount of doping with Dy^(3+) and Eu^(3+) does not change the crystal structure of the matrix SrLaAlO_(4) and the best synthesis temperature is 1450℃.The scanning electron microscopy(SEM) indicates the particle size directly ranges from 1 to 5μm roughly and the energy dispersive spectroscopy(EDS) patterns show that SrLaAlO_(4):Dy^(3+) phosphor and SrLaAlO_(4):Dy^(3+),Eu^(3+) phosphor were successfully synthesized.SrLaAlO_(4):Dy^(3+) phosphor can be effectively excited by near-ultraviolet light,producing two strong emission lights at 483 nm(blue light) and 579 nm(yellow light),presenting a cold white light;SrLaAlO_(4):Eu^(3+) phosphor can be effectively excited by nearultraviolet light,producing red lights at 622 nm;the characteristic emission peaks of Dy^(3+) and Eu^(3+)can be shown simultaneously under the same excitation wavelength in SrLaAlO_(4):Dy^(3+), Eu^(3+) phosphor.By changing the relative doping concentration ratio of Dy^(3+) and Eu^(3+),the modulation of SrLaAlO_(4):Dy^(3+),Eu3+phosphor from cold white to warm white light can be achieved.In addition,the study of the luminescent mechanism and lifetime shows that there is energy transfer between Dy^(3+) and Eu^(3+) in SrLaAlO_(4):Dy^(3+),Eu^(3+) phosphor.

Effects of 4f Electron Characteristics and Alternation Valence of Rare Earths on Photosynthesis: Regulating Distribution of Energy and Activities of Spinach Chloroplast

Chloroplasts were isolated from spinach treated with taCl3, CeCl3, and NdCl3. Because of owning 4f electron characteristics and alternation valence, Ce treatment presented the highest enhancement in light absorption, energy transfer from LHC Ⅱ to PS Ⅱ, excitation energy distribution from PS Ⅰ to PS Ⅱ, and fluorescence quantum yield around 680 nm. Compared with Ce treatment, Nd treatment resulted in relatively lower enhancement in these physiological indices, as Nd did not have alternation valence. La treatment presented the lowest enhancement, as La did not have either 4f electron or alternation valence. The increase in activities of whole chain electron transport, PS ⅡDCPIP photoreduction, and oxygen evolution of chloroplasts was of the following order： Ce〉Nd 〉La〉 control. However, the photoreduction activities of spinach PS I almost did not change with La, Ce, or Nd treatments. The results suggested that 4f electron characteristics and alternation valence of rare earths had a close relationship with photosynthesis improvement.