Synthesis,Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

The Eu³⁺-doped La₂Zr₂O₇ phosphor with rod-like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X-ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to charac-terize its structure and morphology as well as luminescent properties. The results indicated that the red-emitting phosphor La₂Zr₂O₇:Eu³⁺ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as-obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50-700 nm. The pos-sible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La₂Zr₂O₇:Eu³⁺ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive ⁵DO_→⁷F2 _{electric dipole transition of Eu³⁺ ions. Meanwhile, it was more interesting to note that the emission of ⁵D}1_→⁷FJ _{(J=0, 1, 2) transitions and the splitting patterns of ⁵D}0_→⁷FJ _{(J=1, 2, 4) transitions of Eu³⁺ ions can be observed in the luminescent spectra of La2Zr2O7:Eu³⁺. It was demonstrated that Eu³⁺ preferred to occupy a low symmetry site.}     

Comprehensive study on compositional modification of Tb3+ doped zinc phosphate glass

Series of glass composition (60-x) P₂O₅ -40 ZnO –(x) Tb₂O₃ where x = 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol % are prepared by conventional melt quenching technique. X-Ray Diffraction (XRD), FTIR, UV-Vis-NIR and the photoluminescence (PL) spectroscopy are used to characterize the physical, structural and optical behavior of the glass sample. The XRD pattern confirms the amorphous nature and DTA verified the thermal stability of all the glass samples. Glass with 1.5 mol % of Tb₂O₃ possesses the highest thermal stability. Glass density is found to increase proportionally with increasing amount of Tb³⁺ while the molar volume behaves reversely. Six main IR absorption bands centered at about 540, 748, 891, 1085 and 1294 cm^{− 1} are evidenced. The UV-Vis NIR absorption spectra reveals the absorption center band at about 540, 376, 488 and 1920 nm corresponding to the absorption from ⁷F₆ ground state to various excited state of Tb³⁺ ion. The optical band gaps for direct and indirect transition are in the range 4.53–5.07 eV and 4.30 eV-4.56 eV respectively. The Urbach energy decreases with the increasing concentration of Tb₂O₃. The PL emission spectra reveals several prominent peaks at 413, 435, 457, 488, 540, 585 and 620 nm due to electronic transition from ⁵D₃→⁷F₅, ⁵D₃→⁷F₄, ⁵D₃→⁷F₃, ⁵D₄→⁷F₆, ⁵D₄→⁷F₅, ⁵D₄→⁷F₃ and ⁵D₄→⁷F₅ respectively.     

Light absorption by manganese pairs in KMgF3:Mn2+ through a vibronically induced exchange mechanism

Double excitations to ⁴E_g and ⁴A_1g states in manganese pairs of KMgF₃:Mn²⁺ have been studied spectroscopically. Three prominent sharp bands are observed in the low temperature absorption spectrum. These bands are displaced by about 400–500 cm^?1 to higher energies from the expected electronic origins. It is proposed that the observed pair transitions gain their intensity through a vibronically induced exchange mechanism. With this mechanism the symmetric double excitations ⁶A_1g⁶A_1g → ⁴E_gu⁴E_gu, ⁴E_gv⁴E_gv and ⁴A_1g⁴A_1g become allowed in addition to the transition ⁶A_1g⁶A_1g → ⁴E_gu⁴A_1g. Analogy to the spectrum of the linear dinuclear chromium complex [(NH₃)₅CrOCr(NH₃)₅]⁴⁺, where the same mechanism has been postulated, is demonstrated.     

Jahn–Teller coupling and the influence of strain in Tg and Eg ground and excited states – A ligand field and DFT study on halide MIIIX6 model complexes [M = TiIII–CuIII; X = F−, Cl−]

In contrast to well established experimental results of vibronic coupling effects in octahedral dⁿ complexes with E_g ground states (Cu²⁺, Ag²⁺; Cr²⁺, Mn³⁺ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dⁿ cations – in particular for Ti^III, V^III and high-spin Co^III, Ni^III with T_2g and T_1g ground states, which involve, to first-order, solely splitting of the π-antibonding t_2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the T_g ? (?_g + τ_2g) vibronic interaction as well as in the E_g ? ?_g coupling case (Mn^III, low-spin Ni^III); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dⁿ ligand field matrices in O_h, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (Cr^III, ⁴A_2g ground state). The group-theoretical analysis of the interaction with the JT-active ?_g and τ_2g modes yields D_4h, D_3d and D_2h as the possible distortion symmetries in the case of a T_g ground state. The DFT-calculations give clear evidence, that the D_4h stationary points represent the absolute minima in the T_g ? (?_g + τ_2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited T_g states, can be presented for trivalent 3dⁿ cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding e_g MOs.The tetragonal splitting of T_g states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds A^IM^IIIF₄, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for Ti^III to Fe^III; the rather small electronegativity already of Co^III suggests a reducing ligand-to-metal (3dⁿ) electron transfer for n ≥ 6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the Cu^IIIF₆^3? complex and the reduced T_g ? ?_g coupling strength suggest a pronounced covalency of the Cu^III–F, and, even more distinctly, of the Cu^III–O bond, which is of interest for superconductivity. The Ni^IIIF₆^3? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative _a²A_1g(_a²E_g) and _a⁴A_2g (_a⁴T_1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong E_g ? ?_g as compared to the T_1g ? ?_g coupling, which finally stabilises a spin-doublet ground state in D_4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.     

Synthesis of large chelate rings with diphosphites built on a cyclodextrin scaffold. Unexpected formation of 1,2-phenylene-capped α-cyclodextrins

Two primary face difunctionalised α-cyclodextrins (α-CDs) bearing AC and AD-positioned triarylphosphite ligands have been synthesised and their ability to form large chelate rings has been evaluated. 6^A,6^D-Bis-O-{2-〚(diphenoxyphosphino)oxy〛phenyl}-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin (L1) was prepared in three steps in 59% overall yield: (i) treatment of 6^A,6^D-di-O-(methylsulfonyl)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin (1a) with sodium 2-(benzyloxy)phenolate, affording a mixture of the corresponding bisaryloxy substitution product 2a; (ii) cleavage of the benzyl groups of 2a with formation of bisphenol 6a; (iii) reaction of 2a with chlorodiphenylphosphite to afford L1. Diphosphite L2 was obtained in a similar manner using the AC dimesylate 1b (yield: 54%). In step (i) of each synthesis, the unexpected formation of a catecholato-capped CD was observed as a result of benzyl loss under the used arylation conditions. The AD-bridged product was characterised by a single crystal X-ray diffraction study. In the solid state, the CD torus adopts the usual circular shape while four glucose rings, although not distorted, are considerably tilted towards the cavity axis. Both ligands, L1 and L2, when reacted with the cationic complexes AgBF₄ or 〚Rh(norbornadiene)(THF)₂〛X (X = BF₄, PF₆), produced selectively chelate complexes having up to 29-membered metallomacrocycles in high yields. Rhodium systems based on either L1 or L2 catalyse effectively the hyfroformylation of 1-octene (TOF up to 1200 mol mol^–1 of Rh h^–1). Hydrogenation of dimethyl itaconate with a Rh(I)/L2 complex produced dimethyl (R)-(+)-methylsuccinate with an EE as high as 83.6%.     

Der Jahn-Teller-Effekt des Mn3+-Ions in oktaedrischer Fluorkoordination. Ligandenfeldspektroskopische und magnetische Untersuchungen

Jahn-Teller Effect of Mn³⁺ Ions in Octahedral F^?-Coordination. Ligand Field Spectroscopic and Magnetic Investigations From the ligand field spectra of Mn^IIIF polyhedra in different host lattice structures [AB^IMnF₆ (elpasolite type); B^IIMnF₅; A^IMnF₄ (CsFeF₄ type)] remarkable splittings of the octahedral ⁵E_g groundstate as the consequence of a tetragonal (or lower symmetry) Jahn-Teller component are deduced. The splittings vary between 8500 and 15500 cm^?1 and can be correlated with the extent of Jahn-Teller distortion in the Mn^IIIF polyhedra. While the cooperative Jahn-Teller order is of ferrodistortive symmetry in the elpasolite-structure [exception: (NH₄)₃MnF₆], the tetragonally elongated Mn^IIIF octahedra exhibit an antiferrodistortive order in compounds A^IMnF₄, as was possible to conclude from the magnetic structures found at lower temperatures. The intensities of the sharp, spin-forbidden quintet-triplet transitions in the ligand field spectra vary strongly in dependence on the temperature and the cooperative magnetic order observed for the different classes of compounds.     

Circulardichroism—LXXV: Cottonogenic derivatives of chiral bidentate ligands with the complex [Mo2 (O2CCH3)4]

[Mo₂(O₂CCH₃)₄] forms optically active complexes in DMSO after addition ofchiral ligands. Bidentate ligands (carboxylic acids, diols, and amino alcohols) but also a primary amine (α-phenylethylamine) were shown to form these complexes. For molar ratios of less than appr. 1.5:1 (ligand to complex) up to 5 Cotton effects (A to E from 600 to 270 nm) can be observed. The signs of those between 300 and 400 nm can be used for empirical determination of absolute configuration of complexing ligands. Bands A-D are assigned to the following transitions: A: mainly π_Mo-Mo→ δ^* (A_1g→ E_g); B: δ →ρ^*_Mo-O (A_1g → A_2g C: mainly δ → π^*_Mo-Mo (A_1g → E_g ) D: δ → δ^* (A_1g → A_2u ). Sector rules for the pair of CD-bands A/C (hexadecant rule) and for CD-band B (hexadecant rule with two additional nodal planes through the MoO_4- planes) are derived from qualitative MO theory.     

Fine structure of 6A1g → 4A1g, 4Eg (4G) absorption band in MnF2

Systematic spectroscopic measurements of the spectral lines in MnF₂ have been carried out in the temperature range 10–300 K. Observations of exciton and exciton–magnon sidebands in the fine structures of the ⁶A_1g → ⁴A_1g, ⁴E_g (⁴G) state of Mn⁺² ions are reported at low temperatures for MnF₂. The fine structure of the C-band is mainly attributed to spin multiplicity in the ordered state. In addition, the pure exciton bands have been identified and the ratios for the separation energies between these lines are fitted with the ratios expected form Lande interval rule.     

Synthesis and photoluminescence properties of the high-brightness Eu-doped M2Gd4(MoO4)7 (M=Li, Na) red phosphors

A series of red-emitting phosphors Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) have been successfully synthesized at 850 °C by solid state reaction. The excitation spectra of the two phosphors reveal two strong excitation bands at 396 nm and 466 nm, respectively, which match well with the two popular emissions from near-UV and blue light-emitting diode chips. The intensity of the emission from ⁵D₀ to ⁷F₂ of M₂(Gd_1−xEu_x)₄(MoO₄)₇ phosphors with the optimal compositions of x=0.85 for Li or x=0.70 for Na is about five times higher than that of Y₂O₃:Eu³⁺. The quantum efficiencies of the entitled phosphors excited under 396 nm and 466 nm are also investigated and compared with commercial phosphors Sr₂Si₅N₈:Eu²⁺ and Y₃A₅O₁₂:Ce³⁺. The experimental results indicate that the Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) phosphors are promising red-emitting phosphors pumped by near-UV and blue light.     

AB initio Calculations of the structure and spectra of chromium, molybdenum, and tungsten tetrafluorides. nontetrahedral molecular structure of WF4

The properties of MF₄ molecules (M = Cr, Mo, W) are investigated by the restricted Hartree-Fock method using Möller-Plesset second-order perturbation theory and by the second-order configuration interaction method using the multiconfigumtion wave function derived in a complete active space approximation, in wide bases complemented with polarization d and f functions. Relativistic effective potentials are used to describe the core electrons. For CrF₄ and MoF₄, the tetrahedral configuration of nuclei in the electronic state of³k₂ symmetry is energetically most favorable. In the WF4 molecule, the least-energy structure is a D_2h structure in the singlet state ¹A₁. The D_4h,(¹ A_1g) and T_d ( ³A₂) configurations in the WF₄ molecule are higher on the energy scale than the ground state by 4 and 6305 cm’1 and are saddle points. For all of the analyzed configurations of MF₄ molecules, the geometrical parameters, the vibrational spectra, and the energies of vertical electronic transitions are found. The chemical bonding is analyzed and a simple model is proposed to explain the variation of the relative energies of states in the series CrF₄→MoF₄→WF₄.     

Bi-exponential decay of Eu(III) complexed by Suwannee River humic substances: Spectroscopic evidence of two different excited species

The bi-exponential luminescence decay of europium (III) complexed by Suwannee River fulvic acid (SRFA) and humic acid (SRHA), is studied in time-resolved luminescence spectroscopy using two different gratings at varying delay after the laser pulse, increasing accumulation time in order to obtain comparable signals. The two hypotheses found in the literature to interpret this bi-exponential decay are (i) a back transfer from the metal to the triplet state of the organic ligand and (ii) the radiative decay of two different excited species. It is shown that evolutions of the ⁵D₀ → ⁷F₀ and ⁵D₀ → ⁷F₂ luminescent transitions are occurring between 10 and 300 μs delay. First, the ⁵D₀ → ⁷F₀ transition is decreasing relative to the ⁵D₀ → ⁷F₁ showing a slightly greater symmetry of the ‘slow’ component, and is also slightly red shifted. Second, a slight modification of the ⁵D₀ → ⁷F₂ transition is also evidencing a slightly different ligand field splitting. No significant modification of the ⁵D₀ → ⁷F₁ magnetic dipole, which is less susceptible to symmetry changes, is noted in line with expectations. The ⁵D₀ → ⁷F₀ transitions are adjusted with either one or two components. The use of a simple component fit seems to be well adapted for representing an average comportment of these heterogeneous compounds, and a two-component fit constrained by the bi-exponential decay parameters and accumulation times yields in the proposition of the spectra for the fast and slow components.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

Synthesis and luminescence properties of novel red-emitting phosphor InNbO4:Eu3+ for white-light emitting diodes

Red-emitting phosphor InNbO₄:Eu³⁺ was synthesized by the solid-state reaction. Its crystal structure, particle size distribution, and luminescence properties were studied. The powder X-ray diffraction pattern shows that pure InNbO₄:Eu³⁺ was obtained. According to the spectra obtained, this phosphor can efficiently be excited with the light at wavelengths of 394 and 466 nm to emit the strong red radiation at 612 nm due to the ⁵ D ₀→⁷ F ₂ transition of Eu³⁺. The best results were obtained at the concentration of the Eu³⁺ dopant equal to 4 mol.%. The chromaticity parameters of InNbO₄:0.04Eu³⁺ are close to standards of the National Television Standard Committee. Thus, InNbO₄:Eu³⁺ is a promising red-emitting phosphor for white-light emitting diodes.     

Amorphous manganese polyphosphates: preparation,characterization and incorporation of azo dyes

Amorphous Mn²⁺ polyphosphate materials were prepared at room temperature through the coacervation of polyphosphate solutions. These new materials display the typical Mn²⁺ red emission with a broad band centered at 15,290 cm⁻¹ (bandwidth—1,320 cm⁻¹). Excitation spectra display typical Mn²⁺ (d⁵) absorption bands assigned to transitions from the ⁶A_1g ground state to the ⁴T_2g, (⁴A_1g, ⁴E_g), ⁴T_2g, and ⁴T_1g Mn²⁺ excited states. Transition energies allow estimating the Mn²⁺ ligand field strength as intermediate between the one observed in Mn²⁺ aqueous solutions and the one observed in Mn²⁺ phosphate glasses. Azo dyes, methyl red and methyl orange, were incorporated into the manganese polyphosphate coacervates structure. Raman scattering and visible light reflectance results show azo dyes acid forms inside the hydrated polyphosphate structure and sensitivity to the atmosphere pH. Release of azo dyes species was observed from these new solid hybrid materials in aqueous medium.     

Synthesis and isoconversional kinetic study of the formation of LiNiPO<Subscript>4</Subscript> from Ni<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>·8H<Subscript>2</Subscript>O as a new precursor

The nanosized LiNiPO₄ was successfully synthesized by a solid-state reaction between the new Ni₃(PO₄)₂·8H₂O precursor and Li₃PO₄ at 700 °C in air atmosphere. The formation of LiNiPO₄ was generated via three thermal decomposition steps. The samples were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, atomic absorption/atomic emission spectrophotometers, and thermogravimetric/differential thermal gravimetric/differential thermal analysis techniques. The activation energy (E_α) values of the three steps were calculated by Vyazovkin method and determined to be 90.39?±?5.79, 197.81?±?7.46, and 308.66?±?12.03 kJ mol^?1, respectively. The average E_α values from this method are very close to E_α from KAS method. The most probable mechanism functions g(α) of three steps were evaluated by using the masterplots method and found to be the F_1/3 (first step), F_3/2 (second step), and D₄ (final step), respectively. The pre-exponential factors (A) values of three steps were obtained based on the E_α and g(α). The kinetic triplet parameters of the formation of LiNiPO₄ from the new precursor are reported in the first time.     

Impact of Eu3+ Ions on Physical and Optical Properties of Li2O-Na2O-B2O3 Glass

The lithium sodium borate glasses doped with Eu³⁺ ion are prepared using melt quenching technique, their structural and optical properties have been evaluated. The density of prepared glasses exhibits an inverse behavior to the molar volume ranging from 2.26 g/cm³ to 2.43 g/cm³ and 26.95 cm³ /mol to 26.20 cm³ /mol, respectively. The absence of sharp peaks in XRD patterns confirms the amorphous nature of the prepared glasses. The absorption spectra yield four transitions centered at 391 nm (⁷F₀→⁵L₆), 463 nm (⁷F₀→⁵D₂), 531 nm (⁷F₀→⁵D₁), and 582 nm (⁷F₀→⁵D₀). The most intense red luminescence is observed at 612 nm corresponding to ⁵D₀→⁷F₂ transition under 390 nm laser excitations.     

Electronic absorption spectrum of Fe3+ doped in ammonium chloride single crystal

The electronic absorption spectrum of the Fe²⁺ ion doped in ammonium chloride has been studied at room and liquid air temperatures. The observed bands have been assigned transitions from the ground ⁶A_1g(S) state to the excited ⁴A_1g(⁴E_g), ⁴T_1g(G) and ⁴T_2g(G) states. The cubic field approximation with D_q = 675 cm^?1, B = 645 cm^?1 and C = 4.4 B is found to give a good fit to the observed band positions.It is further concluded that the site symmetry of the Fe³⁺ ion in the crystal is lowered from O_h to C_4v symmetry at liquid air temperature.     

Empirical equations for the bond energies and vibrational frequencies at chemisorptive bonds on surfaces

Empirical equations derived for bond energies and force constants of gaseous molecules are applied to chemisorptive bonds on surfaces. For two adsorbed atoms from the same family of the periodic table, A and B, the chemisorptive bond energies, E, to the same metal, M, can be approximated by E_A–M/E_B-M ≈ (E_A2/E_B2)^{$\text{1}\text{2}$}, where E_A2 and E_B2 are the bonds energies of diatomic molecules A₂ and B₂, respectively The corresponding vibrational frequencies, ν, can be approximated by ν²_A–M/ν²_B-M ≈ (m_B/m_A)(F_A2/F_B2)^{$\text{1}\text{2}$} · m_A and m_B are the masses of atoms A and B, respectively;F_A2 and F_B2 are the force constants of molecules A₂ and B₂, respectively. These relations are applied to the chemisorption of halogens on metals and showed good agreement with experiment.     

Hydrothermal homogeneous urea precipitation of hexagonal YBO3:Eu nanocrystals with improved luminescent properties

Well-crystallized YBO₃:Eu³⁺ nanocrystals were prepared by a mild hydrothermal method in the presence of urea, and a pure hexagonal phase could be obtained at a low temperature of 200°C only. The photoluminescence spectra showed a remarkable improvement on the chromaticity as well as the luminescent intensity, compared with the samples synthesized by solid-state reaction (SR). The effects of the synthesis temperature, urea concentration, and the doping concentration of Eu³⁺ on the crystallization and luminescent properties were investigated. The results showed that both high temperature and low urea concentration were favorable to the formation of YBO₃:Eu³⁺, and the ratio of red emission (⁵D₀→⁷F₂) to orange emission (⁵D₀→⁷F₁) increased with decreasing the synthesis temperature and the urea concentration. Furthermore, the samples exhibited a higher quenching concentration of Eu³⁺ in comparison with those prepared by the SR, which was beneficial to further enhancing the luminescent intensity. These synthesis-dependent phenomena were analyzed, and possible explanations were proposed.     

The Eu(III) Ion as Luminescent Probe: Investigation of the Metal-Ion Sites in a Dicyclohexyl-18-crown-6 Complex

The metal ion sites of the 3:2 complex between europium nitrate and the A -isomer of dicyclohexyl-18-crown-6, [Eu(NO₃)₂(DC18C6)]₂[Eu(NO₃)₅], have been probed by high-resolution excitation and emission spectra at 296 and 77 K. The [Eu(NO₃)₅]^2? anion gives rise to a luminescent spectrum dominated by the ⁵D₀→⁷F₂ transition. The crystal-field splitting of the ⁷F_j levels is close to that observed for (Phe₄As)₂[Eu(NO₃)₅], pointing to a structurally similar pentakis(nitrato) species. The ⁵D₀←⁷F₀ excitation spectrum of the two crystallographically independent complex cations displays five maxima. A detailed analysis of the corresponding and selectively excited emission spectra leads to the following conclusions. Well differentiated spectra are assigned to different conformations of the complex cation, in which half of the ligand atoms, including O-atoms, Present large thermal motions. The other spectra are very similar and arise from slightly unequivalent [Eu(NO₃)₂(DC18C6)]⁺ moieties differing in the conformation of their ethylene bridges. This dimonstrates the sensitivity of the Eu(III) ion as conformational probe in the solid state.