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.

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.

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.

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.

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.

Luminescence and energy transfer between Ce^(3+) and Mn^(2+) in alkaline earth borates

The luminescence of Ce and Ce , Mn + co-doped BaB8O13 and SrB4O7 prepared in air is studied. The results show that tetravalent cerium ion can be reduced to trivalent state in the hosts and gives rise to efficient luminescence. Energy transfer between Ce3+ and Mn2+ is possible. Mn2+ ions can be efficiently sensitized by Ce 3+ and exhibit green and red emissions which implied that Mn2 + occupied the crystallographic sites of cations and boron sites of the anoins, respectively. The intensity ratio of red to green emission in matrix increases with the increasing of manganese concentration.

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.

Doped Organic Electroluminescence from a Novel Rare Earth Complex Tb(3-metho)_3phen

A novel rare earth complex Tb(3 metho) 3phen was synthesized and characterized. The complex was doped into PVK to improve the conductivity and film forming property of Tb(3 metho) 3phen. A device with a structure of ITO/PVK∶Tb(3 metho) 3phen /Al was fabricated to study the electroluminescent properties of Tb(3 metho) 3phen. And the optoluminescent and AFM properties of this device were also studied, which proved the existence of energy transfer from PVK to Tb(3 metho) 3phen. As a result, a pure green emission with sharp spectral band at 547.5 nm was observed.

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.

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.

Luminescence properties and energy transfer of host sensitized CaMoO_4:Tb^(3+) green phosphors

A series of CaMoO4：xTb3＋ （x=0.01, 0.03, 0.05, 0.07, 0.09, 0.15 and 0.20） phosphors in pure phase were prepared via high temperature solid-state reaction approach. The crystal structure of the phosphors was investigated by X-ray diffraction （XRD）, and the optical properties were investigated by Fourier transform infrared spectroscopy （FT-IR）, ultraviolet-visible spectroscopy （UV-Vis） and photoluminescence （PL） spectroscopy. The PL spectra illustrated that these phosphors could be efficiently excited by the charge transfer band of the host and the energy transfer efficiency from the host to the doped activator reached 60% when the doping con- centration of the activator Th3＋ was 20 mol.%. The concentration quenching occurred at x= 10 mol.%, from which the critical distance of activator was calculated to be about 1.14 nm. The CIE coordinates were estimated to be close to the standard green value. The host sensitized samples had potential application as green phosphors.

Luminescence of RE^(3+) and energy transfer from Gd^(3+) to RE^(3+) (RE = Dy, Eu) in SrGdAlO_4:RE^(3+)

Spectral properties of Gd3+, Dy3+ and Eu3+ ions in SrGdAlO4 are reported in detail. A cooperative vibronic transition of Gd3+ and the emission from the higher 5DJ (J=1, 2, 3) levels of Eu3+ were observed. Energy transfer occurs from Gd3+ to Dy3+ and to Eu3+. The influence of Gd3+ and Dy3+ concentrations on the luminescence intensity is discussed.

Investigation of 2.9 μm luminescence properties and energy transfer in Tm^(3+)/Dy^(3+) co-doped chalcohalide glasses

A series of chalcohalide glasses based on the composition of 0.9（Ge30Ga5Se65）-0.1CsI with different Tm3＋/Dy3＋-codoped ions concentrations were synthesized by melt-quenching technique.The absorption spectra and 2.9 μm mid-infrared fluorescence spectra of glass samples under 800 nm laser excitation were measured.The results showed that Tm3＋ was an efficient sensitizer,which could enhance the Dy3＋： 2.9 μm fluorescence intensity significantly.The effective energy transfer between the two rare-earth ions were mainly attributed to the resonance energy transfer from Tm3＋：3F4 to Dy3＋：6H11/2 level.Emission cross section of 2.9 μm mid-infrared luminescence was also investigated according to Judd-Ofelt theory,σe=2.51×10–20 cm2.

A stimuli responsive lanthanide-based hydrogel possessing tunable luminescence by efficient energy transfer pathways

Energy transfer as an important component in light-harvesting antenna systems can mimic effectively natural photosynthesis processes,showing great potential in optoelectronic devices.Herein,we report a responsive polymeric hydrogel based on the combination of excited state intramolecular proton transfer(ESIPT) molecule(Salicylic acid,Sal) and terbium(Ⅲ)(Tb^(3+)),as enabled by external stimuli to construct artificial light-harvesting antenna systems.Benefiting from unique photophysical properties of Sal,the synthesized hydrogel displays a temperature-dependent reversible opaque?transparent states transition,accompanied with an interesting photoluminescence behavior.Moreover,by further incorporating europium(Ⅲ)(Eu^(3+)) into the hydrogel,we demonstrate well-defined cascades of energy transfer that provides a tunable optical output from the collection of lanthanides by the excitation of a common sensitizer(Sal) upon base vapor stimulation.Efficient energy transfer efficiency from Tb^(3+) to Eu^(3+),as high as 97.8%,was also obtained as established by the time-resolved fluorescence spectroscopy analysis.

Single-phase white-emitting and tunable color phosphor Na_(3)Sc_(2)(PO_(4))_(3):Eu^(2+),Dy^(3+): Synthesis, luminescence and energy transfer

A series of Eu^(2+)/Dy^(3+) single doped and co-doped Na_(3)Sc_(2)(PO_(4))_(3) phosphors were synthesized by the high-temperature solid-state method,and their phase,morphology,and luminescence properties were characterized.Under the excitation of 370 nm,the Na_(3)Sc_(2)(PO_(4))_(3):Eu^(2+),Dy^(3+) phosphor can emit white light whose spectrum is composed of a broad emission band centered at 460 nm and the other three peaks at 483,577,and 672 nm,respectively.There is energy transfer from Eu^(2+)to Dy^(3+)ion in Na_(3)Sc_(2)(PO_(4))_(3):Eu^(2+),Dy^(3+) phosphor due to the good overlap between the emission spectrum of Na_(3)Sc_(2)(PO_(4))_(3):Eu^(2+) and the excitation spectrum of Na_(3)Sc_(2)(PO_(4))_(3):Dy^(3+),which is further confirmed by the fluorescence lifetime decrease of Eu^(2+)ion with the increase of Dy^(3+) concentration.The process of energy transfer is via dipole–quadruple interaction which is confirmed by applying Dexter's theory.By increasing the Dy^(3+)concentration,the color coordinates of the Na_(3)Sc_(2)(PO_(4))_(3):0.01Eu^(2+),xDy^(3+)phosphors can be adjusted from blue to white,and then to yellow.The optimized concentration of Dy^(3+)ions is 4.0 mol%,beyond which the concentration quenching will take place.The Na_(3)Sc_(2)(PO_(4))_(3):Eu^(2+),Dy^(3+)phosphor shows fairly good resistance to thermal quenching behavior,of which the emission intensity at 423 K can maintain 90.3%of the initial value(298 K).These results suggest that the Na_(3)Sc_(2)(PO_(4))_(3):0.01Eu^(2+),xDy^(3+)phosphors have potential applications as the color-tunable or a single-phase white emitting phosphor in white LEDs.

Nd^(3+)/Yb^(3+) co-doped mid-infrared luminescence fluorobromide glass with energy transfer and zero-thermal-quenching IR emission

Nd^(3+)/Yb^(3+)co-doped fluorobromide glass samples were prepared by melt quenching.The mid-infrared(MIR)luminescence of the Nd^(3+)/Yb^(3+)co-doped fluorobromide glass was investigated by Br-doping reduces the phonon state density of the matrix.The 3.9μm MIR luminescence of the samples excited at 793 and 980 nm pump excitation was investigated in detail.There is an effective mutual energy transfer process between Nd^(3+)and Yb^(3+).It is proved under 793 nm excitation that the luminescence of Nd^(3+)at 3.9μm is reduced by effective energy transfer from,Nd^(3+):2 H11/2→Yb^(3+):2 F5/2,At the same time,it is proved that the effective energy transfer from Yb^(3+):2 F5/2→Nd^(3+):2 H11/2 under the excitation of 980 nm enhances the luminescence of Nd^(3+)at 3.9μm.In addition,it is found that the samples still have good infrared(IR)luminescent properties when the temperature changes.The emission cross-sectional area and the absorption cross-sectional area areσem(3.87×10^(-20)cm^(2))andσabs(4.25×10^(-20)cm^(2)).The fluorescence decay characteristics of the sample at 3.9μm at the 2 H11/2 level were investigated and the fluorescence lifetime was calculated.The gain performance of the sample was calculated and analyzed,which can reach 4.25×10^(-20)cm^(2).Those results prove that Nd^(3+)/Yb^(3+)co-doped fluorobromide glass is the potential mid-infrared laser gain material.

Effects of Gd^(3+) on Luminescence Properties of Eu^(3+) within Polymeric Structure in Aqueous Solutions

?6′ tetracarboxy 4,4′ bipyridine was synthesized and the luminescence enhancement of their Eu 3+ complexes by Gd 3+ was observed. The results indicate that the mechanism of enhancement is based on the formation of a polymeric structure where Eu 3+ and Gd 3+ are linked together by the ligands, which favours the consequent transfer of absorbed energy along the polymeric chain through several ligands toward the Eu 3+ .

Luminescence enhancement of BaMgSiO_4:Eu^(2+) by adding borate as flux

The luminescence of EU^2＋ in BaMgSiO4 with BaB2O4 as flux was studied. The emission spectrum of the phosphor consisted of two bands, peaking at about 398 nm and 515 nm, which were attributed to the emissions from different Eu^2＋ sites in the lattice. When the BaB2O4 flux was applied, the intensity of the 398 nm emission was not clearly affected, but the intensity of the 515 nm emission was enhanced by about ten times. Gaussian fitting showed that the emission band at around 515 nm could actually be resolved into two bands with peak wavelengths of 499 nm and 521 nm, respectively. The assignments of the emission bands to the cation sites were carried out according to the values of bond valence. The overlapping of the 398 nm emission band on the excitation band of 515 nm emission implied that energy transfer could occur from the luminescent center related to the 398 nm emission to the center related to the 515 nm emission, and the energy transfer process remarkably enhanced the intensity of the 515 nm emission band. The phosphor had strong excitation at around 350-400 nm and emitted a bright green luminescence. Thus it could have applications as a green component in solid-state lighting devices assembled by near-UV Light Emitting Diodes （LED） combined with tricolor phosphors.

Green, orange, and red upconversion luminescence in Nd^(3+)/Yb^(3+): Cs_2NaGdCl_6 powders under 785 nm laser excitation

Nd^3＋：Cs2NaGdCl6 and Nd^3＋, Yb^3＋：Cs2NaGdCl6 polycrystalline powder samples were prepared by Morss method E. Under 785 nm semiconductor laser pumping, the upconversion luminescence of Nd^3＋ ions in Cs2NaGdCl6 was investigated at room temperature, and three upconversion emissions near 538 nm （Green）, 603 nm （Orange）, and 675 nm （Red） were observed and assigned to ^4G7/2→^4I9/2, （^4G7/2→^4I11/2; ^4G5/2→^4I9/2）, and （^4G7/2→^4I13/2; ^4G5/2→^4I11/2 ）, respectively. The dependences of these upconverted emissions on laser power and Nd^3＋ ion concentration were investigated, to explore the upconversion mechanism. The effect of doping Yb^3＋ ions on the upconversion luminescence of Nd^3＋ in Cs2NaGdCl6 was also studied under 785 nm laser excitation. The energy transfer processes were discussed as the possible mechanism for the above upconversion emissions.

Spectroscopic properties and energy transfer of Nd^(3+)/Ho^(3+)-doped Ga_2O_3-GeO_2 glass by codoping Yb^(3+) ion

This study presented the luminescence properties of Nd^3＋/Yb^3＋/Ho^3＋ dopant ions inside a host based on Ga_2O_3-GeO_2-Li_2O（GGL） glass. The measured differential scanning calorimetry result showed that GGL glass exhibited excellent stability against devitrification with ？T=135 oC. Obvious 543 and 657 nm emissions were observed in Nd^3＋/Ho^3＋-codoped sample. The incorporation of Yb^3＋ into Nd^3＋/Ho^3＋-codoped glass system had resulted in enhanced upconversion emission intensity under the excitation of 808 nm and/or 980 nm laser diode（LD）. The possible mechanisms and related discussions on this phenomenon were presented. It was noted that the presence of Yb^3＋ yielded an enhancement about 7 and 11 times in the 543 and 657 nm emission intensities respectively under 808 nm excitation due to the energy transfer from Nd^3＋ to Ho^3＋ via Yb^3＋ ion. Here Yb^3＋ played a major role as a bridging ion. While enhanced 543 and 657 nm emission intensities under the excitation of 980 nm LD originated from the sensitization effect of Yb^3＋. Our results showed that Nd^3＋/Ho^3＋/Yb^3＋ triply doped GGL glass might be a promising candidate for the development of visible-laser materials.