5D0 State Research Articles

SrPb3Br8:Pr crystals: growth and investigation of spectroscopic characteristics

Halogenide crystals are of big interest as the functional materials for various applications because of their high transparency in a wide spectral region and a resistance for optical damage. SrPb3Br8 crystals have orthorhombic symmetry Pnma. They are transparent in the 0.36–30µm range, the estimated band gap value is 3.20eV. SrPb3Br8:Pr3+ crystals were grown by the Bridgman method. Transparent boules up to ø15 × 100mm in size were obtained. Fine structure associated with Pr3+ is observed in absorption, photo- and X-ray excited luminescence spectra of SrPb3Br8:Pr. Broad band emission of self- trapped excitons dominates in emission spectra of undoped SrPb3Br8 crystals. Narrow lines in emission spectra are due to radiative transitions from the excited 3P0 and 1D2 states in Pr3+.

Red light emission from europium doped zinc sodium bismuth borate glasses

Zinc sodium bismuth borate (ZNBB) glasses doped with different concentrations of europium were prepared by conventional melt quenching method and characterized through the measurements of density, refractive index, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectra, optical absorption, luminescence and radiative lifetimes. FTIR spectra showed seven characteristic peaks of bismuth and borate functional groups in the range of 400–1600cm−1. The optical band gap and bonding parameters have been calculated from absorption spectra. Photoluminescence spectra recorded in the visible region with 394nm excitation are used to calculate the Judd-Ofelt (JO) intensity parameters (Ω2 and Ω4). The JO intensity parameters have been used to calculate the radiative parameters such as branching ratio (β), stimulated emission cross-section (σse), transition probability (A) for the fluorescent level of 5D0→7F2. Decay rates through single exponential are used to calculate the lifetime (τm) of the meta-stable state 5D0 of (Eu3+ ion) these glasses. The radiative parameters measured for all these glasses show 0.7mol% europium doped zinc sodium bismuth borate glass 5D0→7F2 transition has the potential for red laser applications. The quality of the colour emitted by the present glasses are estimated quantitatively by CIE chromaticity coordinates, which confirms the suitability of these glasses as a red emitting material for field emission technologies and LEDs.

Luminescence and energy transfer studies on Sm3+/Tb3+codoped telluroborate glasses for WLED applications

A new series of Sm3+/Tb3+ codoped telluroborate glasses have been prepared by conventional melt quenching technique with the chemical composition (40−x−y)B2O3+15TeO2+15Li2O+15LiF+15NaF+xTb2O3+ySm2O3 (where x = 0, 0.5; y = 0, 0.05, 0.1, 0.25, 0.5, 1 and 2 wt%). The structural and optical behaviour of the prepared glasses were investigated through Fourier transform infrared spectroscopy (FTIR), optical absorption, photoluminescence and lifetime measurements. The fundamental vibrational units of the borate and tellurite network have been identified through FTIR spectra. Nephelauxetic ratio (β¯) and bonding parameter (δ) values indicate that the SmO bonds are ionic in nature. The characteristic emissions of terbium (543 nm, green) and samarium (645 nm, orange-red) were observed while exciting the Tb3+ ions. Higher magnitude of asymmetric intensity ratio (AIR) values confirms the higher asymmetry around the Sm3+ ion site. Decay profiles of Tb3+ ions (5D4 state) and Sm3+ ions (4G9/2 state) exhibit double exponential nature. The nature of interaction between the donor (Tb3+) and acceptor (Sm3+) has been analyzed through Inokuti-Hirayama (IH) model. Energy transfer from Tb3+ to Sm3+ ions is dominated by dipole-dipole type interaction. TBLT0.5S glass possess the better colour coordinates (0.41, 0.45) and colour correlated temperature (CCT) value (3524 K) and the same is suggested for eye safe warm white light emitting applications.

Efficient repumping of a Ca magneto-optical trap

We investigate the limiting factors in the standard implementation of the Ca magneto-optical trap. We find that intercombination transitions from the 4s5p 1P1 state used to repump electronic population from the 3d4s 1D2 state severely reduce the trap lifetime. We explore seven alternative repumping schemes theoretically and investigate five of them experimentally. We find all five of these schemes yield a significant increase in trap lifetime and consequently improve the number of atoms and peak atom density by as much as ~20x and ~6x, respectively. One of these transitions, at 453 nm, is shown to approach the fundamental limit for a Ca magneto-optical trap with repumping only from the 3d4s 1D2 state, yielding a trap lifetime of ~5 s.

Theoretical Method for an Accurate Elucidation of Energy Transfer Pathways in Europium(III) Complexes with Dipyridophenazine (dppz) Ligand: One More Step in the Study of the Molecular Antenna Effect.

A theoretical protocol to study the sensitization and emission mechanism in lanthanide compounds on the basis of multireference CASSCF/PT2 calculations is proposed and applied to [Eu(NO3)3(dppz-CN)] and [Eu(NO3)3(dppz-NO2)] compounds synthesized and characterized herein. The method consists of a fragmentation scheme where both the ligand and the lanthanide fragments were calculated separately but at the same level of theory, using ab initio wave-function-based methods which are adequate for the treatment of quasi-degenerate states. This is based on the fact that the absorption is ligand-localized and the emission is europium-centered. This characteristic allowed us to describe the most probable energy transfer pathways that take place in the complexes, which involved an ISC between the S1 to T1 ligand states, energy transfer to 5D2 in the lanthanide fragment, and further 5D0 → 7FJ emission. For both compounds, the triplet and 5D2 states were determined at the CASPT2 level to be around ∼26000 and ∼22400 cm-1, respectively. This difference is in the optimal range for the energy transfer process. Finally, the emissive state 5D0 was found at ∼18000 cm-1 and the emission bands in the range 550-700 nm, in quite good agreement with the experimental results.

Luminescent determination of ascorbic acid in dietary supplements

The article presents the results of the ascorbic acid (AA) determination with using a complex of an Tb (III) ion with ciprofloxacin (CF) as a lanthanide luminescent marker. The luminescent properties of the Tb (III)-CF complex in the presence of AA were studied. The excitation and luminescence spectra, triplet level of ligand, the kinetics of the luminescence decay of the Tb(III)-CF complex in the presence of AA were analyzed. The excitation spectrum of the Tb (III)- CF complex has broad bands with maxima at 302 and 355 nm that corresponding to the n→π* electronic transition in the absorption spectrum of ligand. The luminesce spectra demonstrate the emission transitions arising from 5D4 energy level to 7Fj multiplet ground state. The luminescence of the Tb(III)-CF complex was found to be quenched by AA. It was established that the lifetime of the excited 5D4 state of the Tb (III) ion decreases with AA concentration increasing up to 0,25 mg/сm3. Luminescence quenching of the Tb (III)-CF complex by AA follows the Stern-Volmer relationship of AA. The Stern-Volmer constant K is 2478 dm3/mol. The biomolecular quenching rate constant kq is 1,25∙107 dm3/mol. The effect of luminescence quenching of the Tb (III)-CF complex was used to developing the procedure for determining of AA in the dietetic additives «Asvitol» and «Ascorbic acid». The linear calibration plot for AA was obtained over the concentration range of 0,02 to 0,25 mg/сm3.

Photoluminescence Properties of Lanthanide‐Organic Frameworks (LnOFs) with Thiophene‐2,5‐Dicarboxylate and Acetate

S‐heterocyclic dicarboxylic acid, thiophene‐2,5‐dicarboxylic acid (H2TDC), was employed to construct a series of lanthanide‐organic frameworks (LnOFs) with coligand acetate, formulated as [Ln(TDC)(OAc)(H2O)]n [Ln = Eu (1), Tb (2), Gd (3), Dy (4), Sm (5)] under hydrothermal conditions. Structure analysis reveals that 1–5 have dinuclear 3D metal organic frameworks (MOFs), in which TDC2– and OAc– display (κ1‐κ1)‐(κ1–κ1)‐μ4 and (κ2‐κ1)‐μ2 coordination fashions, respectively. The dehydrated products of all compounds show high thermal stability above 410 °C. As for 1, 2, 4, and 5, the photoluminescence analyses exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible region. In particular, compound 2 displays bright green luminescence in the solid state with 5D4 lifetime of 0.510 ms and relative high overall quantum yield of 16 %, based on an ideal energy gap between the lowest triplet state energy level of H2TDC ligand and the 5D4 state energy level of Tb3+. The energy transfer mechanisms in compounds 1 and 2 were also discussed.

Judd-Ofelt modelling and stimulated-emission cross-sections for Tb3+ ions in monoclinic KYb(WO4)2 crystal

Terbium (Tb3+) ions are promising for the development of visible lasers. We report on the spectroscopy of Tb3+ in the monoclinic KYb(WO4)2 (KYbW) crystal, including the Judd-Ofelt (J-O) modelling of the transition probabilities, evaluation of the absorption and stimulated-emission (SE) cross-sections with polarized light, and emission lifetime study. Within the strong configuration interaction (SCI) approximation of the J-O theory, the intensity parameters of Tb3+ are Ω2 =0.864, Ω4 =1.657, Ω6 =1.975 [10-20cm2] and Δ=38810cm–1. The maximum σabs for the 7F6 → 5D4 transition reaches 2.3×10-21cm2 at 486.7nm and the maximum σSE for the green emission according to the 5D4 → 7F5 transition is 2.3×10-21cm2 at 549.3nm (both for E || Nm). The measured lifetime of the 5D4 state for a 1at% Tb3+ doping is 395±5μs. Under blue excitation, Tb: KYbW exhibits intense green emission with the CIE 1931 coordinates of (0.312; 0.644).

Luminescence properties of Eu3+ doped YBO3 for temperature sensing

YBO3:2 at.% Eu3+ was prepared by the solid state reaction and its temperature dependent luminescence was investigated for possible applications in temperature sensing. Phase composition of this material was confirmed by X-ray powder diffraction analysis and excitation and emission spectra were also provided. Under excitation of 355 nm, the fluorescence originating from 5D0 and 5D1 states varied as the temperature rose in a region from 333 to 773 K. The fluorescence intensity ratio (FIR) of 5D0 and 5D1 was investigated which increased significantly with the rise of temperature. The maximal relative sensitivity in the whole temperature range was 1.8% K−1 (at 333 K). The results recommended YBO3:Eu3+ as a new material of the FIR method for non-contact optical thermometry.

Eu:Y2O3 highly dispersed fluorescent PVA film as turn off luminescent probe for enzyme free detection of H2O2

In this work, a novel sensing scaffold consisting highly dispersed Eu:Y2O3 fluorescent flexible film of poly vinyl alcohol (EYCP) was synthesized by simple mixing method and applied to facilitate non-enzymatic detection of hydrogen peroxide (H2O2) by turn off probe of fluorescence. The fluorescence spectra of EYCP consisting number of emission sharp transitions from excited, 5D0→7Fj (j=0, 1, 2, 3, 4) energy levels of doped Eu3+ ion in Y2O3 host. In the presence of H2O2, the fluorescence intensity of the EYCP film was quenched due to the reduction of electron–hole pair recombination in Eu centers by electron transfer from Eu–O excited state to H2O2 energy level rather than 5D0 state of Eu3+, which reduces the number of electron in 5D0 state. The EYCP film shows excellent fluorescence quenching in presence of H2O2 by significantly increasing concentration of H2O2 and completely quenched at ∼150μM. A linear relationship is observed between 0.0 and 60μM with a correlation coefficient of 0.989. H2O2 sensing is also compared with the EYC nanoparticles. This study is expected to have a significant impact on further study of the Eu:Y2O3 fluorescent flexible film for wide range applications.

Studies on the luminescence properties of CaZrO 3 :Eu 3+ phosphors prepared by the solid state reaction method

Abstract CaZrO3:xEu3+ (x = 1.0, 2.0, 3.0, 4.0, and 5.0 mol%) phosphors were successfully prepared by a solid state reaction method. The crystal structure of sintered phosphors was hexagonal phase with space group of Pm-3m. The near ultra-violet (NUV) excitation, emission spectra of the CaZrO3:xEu3+ phosphors were composed of sharp line emission associated with the transitions from the excited states 5D0 to the ground state 7Fj (j = 0, 1, 2, 3, 4) of Eu3+. The results indicated that CaZrO3:xEu3+ might become an important orange-red phosphor candidate for use in white light emitting diodes (WLEDs) with near-UV LED chips. The mechanoluminescence (ML) intensity increases linearly with increasing impact velocity of the moving piston, suggesting that the sintered phosphors can also be useful as a stress sensor.

Synthesis and Photoluminescence Properties of Sc<sub>0.88-x</sub>Lu<sub>0.05</sub>VO<sub>4</sub>:Eu<sup>3+</sup><sub>0.07</sub>,Bi<sup>3+</sup><sub>x</sub> Red Phosphor

Sc0.88-xLu0.05VO4:Eu3+0.07,Bi3+x(0≤x≤0.05) red phosphors were synthesized by solid state reaction at 1200°C for 3h. The structure, morphology and luminescence spectra of samples are investigated by X-ray diffraction (XRD), Scanning electron microscope (SEM) and fluorescence spectrophotometer, respectively. The samples doped with Eu3+, Lu3+ and Bi3+ maintain the body-centered tetragonal structure of ScVO4 and the morphology remains essentially unchanged with slight agglomeration. The excitation spectrum of Sc0.88-xLu0.05VO4:Eu3+0.07,Bi3+x emerged redshift and the excitation intensity increase within the near UV excitation (360-400nm). The optimum doping concentration of Bi3+ is 0.02(x value), and the maximum emission intensity of Sc0.86Lu0.05VO4:Eu3+0.07,Bi3+0.02 is higher than 88 % in comparison with Sc0.88Lu0.05VO4:Eu3+0.07 under 365 nm excitation. Decay curve of 5D0 state for as-prepared samples fits the single order exponential behavior, the lifetime of 5D0 increase first and then decrease with the increase of Bi3+ doping concentration. The internal quantum efficiency is up to 74.08% under 365nm excitation; When the temperature raises to 200°C, the emission intensity maintains 79% of that in the room temperature. Sc0.86Lu0.05VO4:Eu3+0.07,Bi3+0.02 phosphor show high internal quantum efficiency and thermal stability, which is suitable for the UV-pumped white LED as red phosphor.

Downshifting by energy transfer in Eu3+/Yb3+ codoped Ba4La6(SiO4)6O glass ceramics

We report on an efficient near-infrared downshifting in Eu3+/Yb3+ codoped glass ceramics containing Ba4La6(SiO4)6O crystals. The structural and luminescence properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), static and dynamic photoemission and excitation spectroscopy. After crystallization, the doping ions are found to be selectively incorporated into the precipitated oxyapatite crystals on La3+ sites, contributing to the remarkably enhanced visible emission of Eu3+ under 394nm excitation. The Eu3+/Yb3+ codoped glass ceramics additionally exhibits efficient near-infrared luminescence of Yb3+ around 1000nm upon photon excitation of Eu3+ within the 300–550nm range. The reduced visible emission and decay time of 5D0 state with Yb3+ codoping further confirm the energy transfer from Eu3+ to Yb3+, which is promoted due to the shortened distance between Eu3+ and Yb3+ within crystals. The maximum energy transfer efficiency is evaluated to be 61%. It is revealed that energy transfer process occurs predominantly through the cross relaxation of Eu3+(5D0) + Yb3+(2F7/2) → Eu3+(7F6) + Yb3+(7F5/2).

Probing metastable Sm2+ and optically stimulated tunnelling emission in YPO4: Ce, Sm

When the model dosimetry system YPO4: Ce3+, Sm3+ is exposed to X-rays, the charge state of the dopants changes, becoming Ce4+ and Sm2+ via hole and electron trapping, respectively which are metastable; the original charge states can be achieved through electron transfer back from Sm2+ to Ce4+ via optical stimulation. The work presented here adds further details to the energy levels of the metastable Sm2+ defect and the electron transfer processes by undertaking measurements of a) Sm2+ excitation spectrum through the internal 5D0 → 7F2 emission at 7 K, b) relaxation lifetime of Sm2+ (5D0 state) and its temperature dependence to provide insights into thermal quenching, and c) the kinetics of localised recombination from Sm2+ to Ce4+ on nanoseconds to seconds time scales using sub-band-edge excitation.

Europium doping in monoclinic KYb(WO4)2 crystal

We report on a detailed spectroscopic study of Eu3+ ions in the monoclinic KYb(WO4)2 crystal. The polarized room and low-temperature absorption spectra are measured. The maximum σabs corresponding to the 7F1 → 5D1 transition is 1.32×10–20cm2 at 534.2nm with a bandwidth of 0.7nm (for E||Nm). The Stark sub-levels of the excited mulitplets are determined. A Judd-Ofelt analysis is applied to the Eu3+:KYb(WO4)2 crystal to determine the probability of spontaneous transitions, radiative lifetimes and luminescence branching ratios. Within the strong configuration interaction (SCI) approximation, the intensity parameters are Ω2=4.757, Ω4=2.295, Ω6=1.644 [10–20cm2] and Δf=50160cm–1. The radiative lifetime of the 5D0 state is 351 µs. The maximum stimulated-emission cross-section corresponding to the 7F1 → 5D1 transition is 1.44×10–20cm2 at 703.2nm (for E||Nm). Under UV excitation, the Eu3+:KYb(WO4)2 crystal provides intense red photoluminescence with CIE coordinates, x=0.675, y=0.325.

Accurate electron affinity of V and fine-structure splittings of V- via slow-electron velocity-map imaging.

We report the high-resolution photoelectron spectra of negative vanadium ions obtained via the slow-electron velocity-map imaging method. The electron affinity of V was determined to be 4255.9(18) cm-1 or 0.527 66(20) eV. The accuracy was improved by a factor of 60 with regard to the previous measurement. The fine structure of V- was well resolved: 35.9(11) (5D1), 103.8(12) (5D2), 204.17(74) (5D3), and 330.58(40) cm-1 (5D4) above the ground state 5D0, respectively.

Excitation and emission of Pr3+:PLZT ceramics

Excitation and emission spectra of Pr3+:PLZT ceramics have been studied. Several emission bands were measured under blue laser excitation, which correspond to 3P0→3H4, 1D2→3H4, 3P0→3H4 and 3P0→3F2 transitions of trivalent Pr3+. Their integrated emission intensities were determined. The blue-to-red luminescence intensity ratios of Pr3+ depend significantly on free sintering/hot pressing methods used for PLZT fabrication and activator concentration. Luminescence decay curves for the 1D2 state of Pr3+:PLZT ceramics are also presented and discussed.

Crystal Structures of New Lanthanide Hydroxybenzoates and Different Roles of LMCT State in the Excitation Energy Transfer to Eu3+ Ions

AbstractA series of europium and terbium hydroxybenzoates [Eu(2‐OH‐Benz)3(H2O)] (1), [Eu(3‐OH‐Benz)3(H2O)3]2⋅2H2O (2), TbNa3(2‐OH‐Benz)3⋅3H2O (3), [Tb2(3‐OH‐Benz)6(H2O)4]⋅2H2O⋅0.5(3‐OH‐HBenz) (4), [Tb(4‐OH‐Benz)3]⋅H2O (5) has been prepared and investigated using X‐ray diffraction and luminescence spectroscopy. Two methoxysalicylates Ln2(2‐OH‐5‐OCH3‐Benz)3⋅6H2O (Ln=Eu, Tb) are also under consideration. A dimeric crystal structure of 2 and polymeric structures of 4 and 5 were first determined by single crystal X‐ray analysis. Low‐energy ligand‐metal charge transfer (LMCT) states caused by a particular binding of the ligands with Ln3+ ion were identified in the europium compounds. Different roles of the LMCT states located under and above the lowest triplet state of the ligand in the excitation energy transfer in europium hydroxybenzoates are discussed. The lifetimes of 5D0 (Eu3+) and 5D4 (Tb3+) states at 77 K are consistent with the number of water molecules and other quenchers containing in the compounds. A qualitative correlation is observed between the luminescence brightness of hydroxybenzoates and an efficiency of nonradiative processes caused by the LMCT state and directly the multiphonon relaxation. Nonradiative processes due to the LMCT state are the most efficient at the location of this state lower the lowest triplet of 2‐hydroxybenzoate ligand in complex 1.

Luminescent polymer electrolytes based on chitosan and containing europium triflate

Solid polymer electrolytes based on chitosan and europium triflate were prepared by solvent casting and characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence spectroscopy. The X-ray diffraction exhibited that the samples were essentially amorphous with organized regions over the whole range of the salt content studied. The AFM analysis demonstrated that the smoother sample had roughness of 4.39 nm. Surface visualization through SEM revealed good homogeneity without any phase separation for more conductive samples and the less conductive showed some imperfections on the surface. The emission and excitation spectra displayed the characteristic bands of Eu(CF3SO3)3 in addition to broad bands corresponding to the polymer host. The excited state 5D0 lifetime values ranged from 0.29–0.37 ms for the studied samples.

Enhancement of luminescence intensity and spectroscopic analysis of Eu3+-activated and Li+ charge-compensated CaTiO3 color tunable phosphors for solid-state lighting

The present work explores a well-crystallized perovskite calcium titanate (CaTiO3) doped with trivalent europium (Eu3+) and co-doped with lithium ion (Li+) successfully synthesized by a conventional solid-state reaction method, and the impact of single dopant and co-dopant on the photoluminescence performances of the sample has been investigated by emission, excitation and diffuse reflectance spectra at the room temperature. Photoluminescence spectra of Li+-doped CaTiO3:Eu3+ nanophosphor revealed at intense pink emission peak for Ca(0.85−y)Li y TiO3:0.15Eu3+ nanophosphor around wavelength 619 nm in the visible region upon the excitation of near-UV light at wavelength 397 nm due to 5 D 0 → 7 F 2 transition in Eu3+. The incorporation of Li+ ion on CaTiO3:Eu3+ nanophosphors enhanced the emission probability from higher 5 D 0 state to lower 7 F j state, and its PL intensity is found to be three times greater than the intensity of CaTiO3:Eu3+ nanophosphor. The spectral characteristics and the Eu–O ligand behavior were confirmed in light of Judd–Ofelt theory from the Emission spectra rather than absorption spectra. Their crystal structure was confirmed by X-ray diffraction (XRD) which is in good agreement with pure orthorhombic phase with space group Pbnm, and it also indicated that the incorporation of the dopant/co-dopant did not affect the crystal structure. The experimental observation reveals that the developed phosphor material Li+-co-doped CaTiO3:Eu3+ can be used in solid-state lighting devices.