Intramolecular energy transfer in mesogenic europium (III) adduct

The absorption and emission spectra of a liquid-crystalline melt prepared on the basis of a synthesized mesogenic europium (III) adduct are studied in the temperature range from 77 to 348 K. The main channels and rate constants of intramolecular energy transfer from ligands to Eu (III) ions are determined from the absorption and luminescence spectra and luminescence kinetics of the sample under study. It is shown that the liquid-crystalline melt of the europium (III) adduct has a high photostability and an intense luminescence in the temperature range from 77 to 300 K, which allows one to consider it as a promising material for optoelectronic devices. Above room temperature, the relaxation time of the ⁵ D ₀ level of Eu (III) ions sharply shortens. An analysis of the kinetics of the luminescence corresponding to the ⁵ D ₀ → ⁷ F ₂ transition shows that the relaxation of the ⁵ D ₀ level in the temperature range from 300 to 348 K occurs through a charge-transfer state.     

Luminescent Properties of Hybrid Nanostructures Based on Quantum Dots of CdS,Europium 1,3-Diketonate,and Methylene Blue Molecules

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu³⁺ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu³⁺ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu³⁺ ions in the CdS/CdS:Eu³⁺ and CdS/TGA/Eu³⁺ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu³⁺, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu³⁺ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu³⁺ ions to methylene blue molecules takes place.     

Luminescence properties of transparent ceramics Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Yb

We present the results of studying the luminescence properties of transparent ceramics Y₃Al₅O₁₂:Yb obtained by the vacuum sintering and nanocrystalline technology. In the course of research, we measured the luminescence and luminescence excitation spectra, as well as the temperature and kinetic behavior of luminescence. Our results are analyzed in comparison with the characteristics of corresponding single crystals. We revealed that processes of generation and relaxation of electronic excitations that occur in ceramics, in particular, in the charge transfer state, are similar to processes occurring in crystals. The behavior of two charge-transfer luminescence bands at 340 and 490 nm is studied. In the range 300–600 nm, we revealed a broad emission band of radiation of other type, which is also observed in spectra of undoped ceramics. This broad band is attributed to F⁺ centers. Emission and excitation spectra of charge transfer luminescence at a maximum of the temperature dependence of 100 K are measured for the first time. We found that, upon excitation in the charge transfer band, luminescence in ceramics is more intense than in single crystals with similar concentrations of Yb and has a higher quenching temperature.     

Luminescence of Eu<Superscript>3+</Superscript> ions in ultradisperse diamond powders

The luminescence of Eu³⁺ ions implanted in ultradisperse diamond powders, activated by impregnating with a solution of Eu(NO₃)₃·6H₂O and heat-treated at various temperatures, is studied. A multiple increase in the efficiency of excitation in the charge-transfer band is observed for the ⁵D₀ state of Eu³⁺ ions as compared to europium nitrate heat-treated similarly. This effect is explained by an increase in the degree of Eu-O bond covalency and a change in the activator coordination polyhedron due to the formation of chemical bonds Eu-O-C.     

Europium luminescence in fluorite upon high-energy excitation

The reflection and luminescence excitation spectra of CaF₂ crystals containing europium ions in divalent (Eu²⁺) and trivalent (Eu³⁺) states were measured in the range from 4 to 16 eV. It was established that, in CaF₂ : Eu³⁺ crystals, luminescence of Eu³⁺ ions (the f-f transitions) is effectively excited both in the charge-transfer band (at ～8 eV) and in the region of the 4f–5d transitions (at ～10 eV) but is virtually not excited in the fundamental region of the crystal (at an energy higher than 10.5 eV). Luminescence of Eu²⁺ ions (the 427-nm band) in CaF₂ : Eu³⁺ is effectively excited in the fundamental region of the crystal; i.e., luminescence of divalent europium ions occurs through the trapping mechanism. Emission of Eu²⁺ ions in CaF₂ : Eu²⁺ crystals is characterized by the excitation band at an energy of 5.6 eV (the 4f → 5d,t _2g transitions), as well as by the exciton and interband luminescence excitations. The results obtained and data available in the literature are used to construct the energy level diagram with the basic electron transitions in the CaF₂ : Eu crystals.     

Eu3+激活的硼钒酸钇的光致发光

找出了合成Eu3+激活的硼钒酸钇铕发光粉的适宜条件和发光最佳化学组分,它是(Y0.94Eu0.06)(V0.69B0.31)O3.7.对其发光光谱的温度依赖关系的研究指出,发光最佳温度在350℃左右.发光的这种温度依赖关系与基质和Eu3+对能量的吸收,以及基质向Eu3+能量传递效率的提高有关.此外,试验结果还表明,在365nm激发下,少显Gd2O3、Zn2GeO4·GeO2:Mn2+等添加剂的加入提高了样品的发光亮度.     

Luminescence of europium ions in lanthanum-magnesium hexaaluminate

The photoluminescence of Eu³⁺ ions in hexagonal lanthanum-magnesium aluminate is studied for the first time. The concentration and temperature dependences of the luminescence intensity and the structure of the spectra of La_1–xEu_xMg·Al₁₁O₁₉ for X = 0.01–1.0 were studied, the existence of several types of luminescence centers (LC) was established. Under excitation, predominantly high-symmetry LC (D_3h) are manifested in the charge-transfer band in the luminescence spectra. A group-theoretical analysis of the structure of the luminescence spectra of europium for possible LC in hexaaluminate with the structural type of magnetoplumbite (space group P6₃/mmc) is carried out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 45–49, October, 1985.We thank our co-workers at the Laboratory of Vibrations, Institute of General Physics of the USSR Academy of Sciences, for assistance in the experiments on selective laser spectroscopy.     

Spectroscopic studies on the luminescence properties of ternary europium complexes with different ligands

In this paper, ligand effect of several bi-dental oxygen (O) and nitrogen (N) ligands on the red luminescence properties of europium ion (Eu³⁺) was studied comprehensively. Absorption, emission, and excitation spectral properties of ternary europium complexes with different combinations of ligands including thenoyl trifluoroacetone (TTA), naphthyl trifluoroacetone (NTA), 2,2′-bipyridyl (bpy) and phenanthroline (Phen) were investigated. Efficient Eu³⁺ red emission was observed with all the combinations of the above mentioned ligands. The most intense emission was found with the all nitrogen coordinated complex Eu(bpy)₂(Phen)₂ while the longest wavelength excitation band was recorded with oxygen-nitrogen mixed NTA-bpy complex Eu(NTA)₁(bpy)₃. With change of the ligands combination and ratio, the Eu³⁺ emission peak changes slightly from 612 to 618 nm. The absorption and excitation spectra of the europium complexes were compared and analyzed referring to the individual absorption spectral properties of the ligands. The relation between ligand-to-metal charge transfer states and luminescence intensities for different complexes was studied.     

Europium doped strontium borate glasses and their optical properties

Optical absorption and luminescence spectra of europium doped strontium borate glasses prepared in different conditions are studied. It is found that the percentage of Eu³⁺ ions varies from 100 to 30% being controlled by the conditions of preparation. The mechanism, favoring reduction of europium to Eu²⁺ state in polycrystalline strontium tetraborate, is much weaker in glasses of the same composition. In samples containing mixed valence europium at densities of 8×10²⁰ cm⁻³, the efficient transfer of optical excitation from Eu³⁺ to Eu²⁺, suppressing the Eu³⁺ luminescence, has been found. The most reliable way of monitoring the percentage of europium ions in different valences for strontium borate glasses is the measuring of absorption at f-f transition ⁷F₀→⁵D₂ of Eu³⁺.     

Luminescence channels of manganese-doped spinel

Two independent luminescence channels are observed from manganese-doped spinel Mn:MgAl₂O₄. The luminescence around 520 nm is assigned to transition from the lowest electronic excited state ⁴T₁ to the ground state ⁶A₁ of Mn²⁺ (3d)⁵ ion by analyzing the excitation spectrum and electron spin resonance measurement. The emission at 650 nm is triggered by the band edge excitation and is assigned similarly to the charge-transfer process associated with the manganese ion.     

Spectroscopic properties of 2-phenylbenzothiazole and 1-phenylpyrazole luminophores metalated with platinum metals

The effect of metalation of 2-phenylbenzothiazole and 1-phenylpyrazole with Pd(II), Pt(II), and Rh(III) on the structure and optical properties of luminophore complexes is studied by ¹H NMR spectroscopy, IR spectroscopy, and electronic absorption and emission spectroscopy. It is shown that metalation of luminophores leads to the formation of five-membered {M(C??N)} fragments in the composition of square planar and octahedral complexes, which exhibit a long-wavelength charge-transfer band. The luminescence properties of the complexes are characterized by quenching of the fluorescence and by enhancement of the phosphorescence from the mainly intraligand excited state. Fluorescence quenching of complexes is attributed to the thermally activated energy transfer to metal-centered states and their efficient nonradiative decay.     

Spectroscopic Study of the Photophysical Properties of Rare Earth Ions Encapsulated: Water Soluble Functional Calixresorcin[4]Arene

Abstract

A novel macrocyclic compound-water soluble functional calixresorcin[4]arenes—tetra para sulfo-phenylmethyl-calixresorcin[4]arenes was synthesized for the first time. the photophysical properties of terbium and europium ions encapsulated in the macrocyclic ligand were studied in detail. the triplet state energy of the calixresorcin[4]arene was determined to be 24400 cm^?1 by the low temperature phosphorescence spectrum and it was found that it can sensitize both terbium ion and europium ion. the possible energy transfer process between the functional calixresorcin[4]arene and the encapsulated Tb³⁺ and Eu³⁺ was discussed. the luminescence quantum efficiency of Tb³⁺- calixresorcin[4]arene was calculated.     

Sensitization of Europium Luminescence in Complexes with Thiaprophenic Acid

The sensitized luminescence of europium ion in complexes with thiaprophenic acid has been investigated. It is shown that the luminescence intensity of the Eu (III) increases by 10⁷ times as the result of intramolecular energy transfer from ligand to lanthanide ion. The luminescence properties of the complex have been studied in solutions and a highly sensitive luminescence method for the determination of thiaprophenic acid has been developed.     

Enhanced UV-excited luminescence of europium ions in silver/tin-doped glass

Glasses containing silver, tin and europium were prepared by the melt-quenching technique with silver nanoparticles (NPs) being embedded upon heat treatment (HT). An intensification of Eu³⁺ ions emission was observed for non-resonant excitation around 270 nm, corresponding to UV absorption in the material. Optical measurements suggest that light absorption occurs at single Ag⁺ ions and/or twofold-coordinated Sn centers followed by energy transfer to europium which results in populating the ⁵D₀ emitting state in Eu³⁺. After HT at 843 K, a quenching effect is observed on Eu³⁺ luminescence with increasing holding time in the 350–550 nm excitation range. The quenching effect shows with the presence of Ag NPs which may provide multipole radiationless pathways for excitation energy loss in europium ions.     

Luminescence and relaxed excited state origin in CsI:Pb crystals

Emission and excitation spectra, luminescence polarization and decay kinetics have been studied for CsI:Pb crystals in the 0.36-300 K temperature range. The origin of the excited states responsible for the optical characteristics has been discussed. It has been concluded that the doublet ≈3.70 eV absorption (excitation) band is caused by the electronic transitions into the Pb²⁺ triplet state split due to the presence of a cation vacancy near a Pb²⁺ ion, while the higher-energy bands are of the charge-transfer origin. Like in CsI:Tl, four emission bands of CsI:Pb have been found to belong to the main luminescence centres. Two emission bands, peaking at 3.1 and 2.6 eV, are suggested to arise from the triplet relaxed excited state of a Pb²⁺ ion. Two visible emission bands, peaking at 2.58 and 2.23 eV, are interpreted as the luminescence of an exciton localized near the Pb²⁺ ion.     

Experimental determination of the charge-transfer exciton band width in anthracene-PMDA crystal

The charge-transfer (CT) exciton is investigated on the reflection and luminescence spectra of isotopically mixed anthracene-PMDA crystals. The observed features are analyzed by the coherent potential approximation. It is concluded that the CT exciton in this crystal has the band width of about 100 cm^?1.     

Luminescence and energy transfer in La2O3–Nb2O5–B2O3:M3+ (M=Bi,Eu, Dy) glasses

The luminescence and energy transfer processes in La₂O₃–Nb₂O₅–B₂O₃:M³⁺ (M=Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy (excitation and emission, down to 4.2 K) and decay time measurements at room temperature. The observation of niobate luminescence implies a considerable degree of short- and intermediate-range order in these glasses. Energy transfer from the niobate groups to the lanthanide ions was observed for Eu³⁺, but not for Dy³⁺, suggesting that the energy transfer process occurs to the charge-transfer state of the Eu³⁺ ion, rather than to its f-levels. Inter-Eu³⁺ energy transfer was negligible in the concentration range investigated (up to 3 mol%). In contrast, cross-relaxation processes between Dy³⁺ ions were active at concentrations as low as 0.5 mol%. In the Bi³⁺ doped glasses the energy transfer was observed from the Bi³⁺ excited levels to the oxygen deficient niobate groups.     

Quantum cutting abilities of sol-gel derived LiGdF4:Eu powders

Optical properties of europium doped LiGdF₄ (LGF) powders synthesized by the sol-gel process were investigated in the VUV range. Emission of two visible photons (due to ⁵D₀→⁷F_J transitions on two Eu³⁺ ions) per absorbed VUV photon was demonstrated indicating that a quantum cutting phenomenon takes place. This mechanism is explained by a two-step energy transfer when exciting Gd³⁺ ions in their ⁶G_J high energy level. Best luminescence efficiency was recorded at room temperature for samples with a doping rate of 5 mol% in europium ions. Effect of rare-earth concentration on internal quantum cutting efficiency was studied. Temperature dependence was also investigated and showed that the down-conversion process upon excitation at 202 nm becomes inefficient at low temperature since energy transfer from Gd³⁺ ions to Eu³⁺ ions is not effective any more. Such a result was connected with the thermal population at room temperature of Eu³⁺⁷F₁ state which is involves in the first step of the energy transfer.     

借助功能阳离子实现敏化发光的铕配合物的溶剂效应的研究

在离子缔合型铕配合物Eu(tta)₄·DEASPI中,借助功能阳离子DEASPI的电荷转移激发态可以实现对铕离子的单光子与双光子的敏化发光,其能量传递遵循Förster机制。将Eu(tta)₄·DEASPI溶解于多种有机溶剂中(丙酮、DMF、乙醇和乙腈),发现溶剂效应对于该能量传递体系的影响非常显著。借助光谱测量,发现在乙腈溶液中能量传递效率远高于其他三种溶剂。本文对造成溶剂效应的多种因素进行了详细的分析。     

Structure and luminescence of CsI:Eu columnar films

Europium doped columnar films of CsI are produced by vacuum condensation. Eu²⁺ ions in the CsI:Eu films lead to the formation of a narrow (0.18 eV), intense luminescence band with a maximum at 456 nm, which is excited by x-rays, as well as by photons of various energies. The spectral and kinetic characteristics of the emission depend on the amount of activator and on the conditions under which the film is prepared and stored. The nature of the luminescence centers is determined by structural formations that contain divalent europium ions.