Luminescent Properties of a Polymer Photoluminescent Composite Containing the Binuclear (EU,TB) Complex as an Emitter

Uninuclear europium (Eu), as well as binuclear Eu and terbium (Tb), complexes were synthesized using acrylic acid (AA) as the first ligand and 1,10-phenanthroline (Phen) as the second ligand. The relative weight ratio of the europium (III) (Eu³⁺) to terbium (III) (Tb³⁺) ions of the binuclear complex was 1:1 as determined via energy dispersive X-ray analysis. The structures of the Eu(AA)₃Phen and Eu_0.5Tb_0.5(AA)₃Phen complexes were characterized by Fourier transform infrared spectroscopy. A series of tri-cellulose acetate (TCA)/ the Eu(AA)₃Phen and TCA/Eu_0.5Tb_0.5(AA)₃Phen composites were prepared by solution blending, and their luminescent properties were investigated by fluorescence spectrophotometry. The excitation spectra of all composites indicated that the TCA matrix probably affected the energy absorption and transfer of organic ligands. In TCA/Eu_0.5Tb_0.5(AA)₃Phen composites the introduced Tb³⁺ ions had some influence on energy absorption and transfer of organic ligands; the energy transfer process of the complex is suggested to be as follows: Phen→AA→Tb³⁺ion→Eu³⁺ion. The emission spectra indicated that the luminescent intensity of the TCA/Eu_0.5Tb_0.5(AA)₃Phen composites was noticeably stronger than that of the TCA/Eu(AA)₃Phen composites, suggesting that the comparatively stable and high-efficiency energy transfer process was only slightly influenced by the TCA matrix. In summary, the TCA/Eu_0.5Tb_0.5(AA)₃Phen (90/10) composite possesses fine luminescent properties for potential usage as red fluorescent materials.     

Development of electroluminescence cell using a Eu0.5Y0.5(TTA)3Phen organic luminescent complex

Novel red emitting organic luminescent complexes, namely Eu_0.5Ln_0.5(TTA)₃ Phen (Eu: europium, Ln: Y/Tb, Y: yttrium, Tb: terbium, TTA: thenoyl tri fluoro acetone, Phen: phenanthroline) were synthesized by solution technique, maintaining stoichiometric ratio. These complexes were characterized by various techniques such as XRD, optical absorption and photoluminescence (PL) spectra. Electroluminescence cells were designed by sandwiching Eu_0.5Ln_0.5(TTA)₃Phen between indium tin oxide (ITO) and aluminum (Al). Voltage?current characteristics and voltage?brightness characteristics of the developed electroluminescent cell were carried out. Turn on voltage of both the devices was found to be 9 V. These devices emit intense red emission at 611 nm, proving their potential applications as organic light emitting diodes and displays.     

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.     

Analysis on fluorescence of dual excitable Eu(TTA)3DPBT in toluene solution and PMMA

Photoluminescence of Eu(TTA)₃DPBT (TTA=thenoyltrifluoro-acetonate DPBT=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) in toluene and PMMA thin film are measured with excitation at 350 and 404 nm, respectively, and analyzed using Judd-Ofelt theory. Under excitation at 350 nm, it is found that Eu(TTA)₃DPBT in toluene has a larger Ω₂ value (14.33×10⁻²⁰ cm²) than that (12.70×10⁻²⁰ cm²) of Eu(TTA)₃Phen (Phen=1,10-phenanthroline) in the same solvent, and has a smaller Ω₂ value (12.70×10⁻²⁰ cm²) in PMMA than that (Ω₂=14.09×10⁻²⁰ cm²) of Eu(TTA)₃Phen in PMMA. At the same time, it can be seen that under excitation at 350 nm Ω₂ value of Eu(TTA)₃DPBT in toluene is larger than that in PMMA. Excited by 404 nm, Ω₂ of Eu(TTA)₃DPBT obtained in toluene and in PMMA are the same as that excited at 350 nm. The transition probability (A), emission cross-section (σ) and the fluorescence branching ratio (β) are also evaluated. The lifetime of ⁵D₀ metastable state is measured on 350 and 404 nm excitation, respectively. For the former situation, it is 455 μs in toluene and 640 μs in PMMA, for the latter it is 460 μs in toluene and 664 μs in PMMA. By comparing absorptions with excitations, it can be found that DPBT is more efficient than TTA as an energy donor. Phosphorescence spectra are also measured to estimate the lowest triplet level and analyze the energy transfer for DPBT and TTA, from which it is found that the energy transfer from TTA to DPBT occurs in the luminescent process.     

Enhanced electroluminescence of Eu by Tb in complexes Tb1−xEux(TTA)3Dipy

A series of rare earth ternary compounds of Tb_1−xEu_x(TTA)₃Dipy (HTTA=thenoyltrifluoroacetone, Dipy=2,2′-dipyridyl) have been synthesized, and the characteristics of the compounds have been performed by DTA-TG, IR, UV and fluorescence spectroscopy. Photoluminescence measurements indicated that the complexes of Eu(III) emit strong red luminescence under UV radiation. IR spectra suggest that complexes have been successfully synthesized, and TG curves indicate that the complexes are stable up to a temperature of about 220 °C. The Eu complex was blended with poly(N-vinylcarbazole) (PVK) and spin coated into films, and electroluminescence devices with the structure of Indium Tin Oxide (ITO)/PVK:Tb_1−xEu_x(TTA)₃Dipy/BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)/aluminum quinoline (AlQ)/Al were fabricated, the luminescence of Eu³⁺ complexes enhances after doping with Tb³⁺. Therefore, it may be an effective method to improve the EL intensity of the lanthanide complex.     

Luminescence and crystal field analysis of Eu in Eu[Co(CN)6]·4H2O

The vibrational spectra of Eu[Co(CN)₆]·4H₂O and luminescence spectra of Eu³⁺ in this compound, using 355 nm excitation at temperatures down to 10 K, have been assigned. A clear distinction is made between the n=5 and 4 members of the Ln[M(CN)₆]·nH₂O series from the vibrational spectra. The electronic spectra show prominent vibronic structures, particularly for the ⁵D₀→⁷F₂ sideband. A resonance occurs between the transitions ⁵D₀→⁷F₁(III) and ⁵D₀→⁷F₀+ν(Eu−N). A crystal field analysis of the derived energy data set is presented for Eu³⁺ in eight coordination geometry.     

Assemblies, characterization, and luminescent enhancement of organized molecular films based on rare earth complexes

Langmuir-Blodgett (LB) films of different molar percentages of Eu(TTA)₃Phen (TTA=2-thenoyltrifluoroacetone; Phen=1,10-phenanthroline) with Gd(TTA)₃Phen coexisting with arachidic acid (AA) (complexes:AA=1:l, in molar ratio) were fabricated and the luminescence enhancement of Eu(III) in the films was studied in this investigation. The monolayers and LB films were characterized by π-A isotherms, fluorescence microscopy, UV-vis spectroscopy and low-angle X-ray diffraction. High-quality LB films and strongly luminescent films were obtained. It was learned from the present study that an efficient intermolecular energy transfer occurred from Gd(TTA)₃Phen to Eu(TTA)₃Phen in the films, which resulted in the luminescence enhancement effect. According to the proposed model of the “active enhancement circle” the distance of energy transfer from Gd-, Tb-, La-, and Y-complex to Eu-complex were calculated to be 1.2, 1.2, 0.7 and 1.0 nm, respectively.     

Role of methylene spacer in the excitation energy transfer in europium 1- and 2- naphthylcarboxylates

A series of compounds Ln(RCOO)₃·Phen (Ln=Eu, Gd, Tb; RCOO⁻-1- and 2-naphthoate, 1- and 2-naphthylacetate, 1- and 2-naphthoxyacetate anions, Phen-1,10-phenanthroline) was investigated by methods of optical spectroscopy. Compounds of composition Ln(RCOO)₃·nH₂O with the same carboxylate ligands are also considered. Results of studies of the effects of methylene spacer decoupling the π-π- or p-π-conjugation in the naphthylcarboxylate ligand on the structure of Eu³⁺ coordination centre, on the lifetime of ⁵D₀ (Eu³⁺) state, and on processes of the excitation energy transfer to Eu³⁺ or Tb³⁺ ions are presented. Introduction of the methylene bridge in the ligand weakens the influence of the steric hindrances in forming of a crystal lattice and results in lowering the distortion of the Eu³⁺ luminescence centre, and in elongation of the observed ⁵D₀ lifetime τ_obs. The latter is caused by decrease in contribution of the radiative processes rate 1/τ_r. This is confirmed by the correlation between the lifetimes τ_obs and the quantities “τ_r·const” inversely proportional to the total integral intensities of Eu(RCOO)₃·Phen luminescence spectra. The methylene spacer performs a role of regulator of sensitization of the Ln³⁺ luminescence efficiency by means of an influence on mutual location of lowest triplet states of the ligands, the ligand-metal charge transfer (LMCT) states, and the emitting states of Ln³⁺ ions. The lowest triplet state in lanthanide naphthylcarboxylate adducts with Phen is related to carboxylate anion. A presence of the methylene spacer in naphthylcarboxylate ligand increases the triplet state energy. At the same time, the energy of “carboxylic group-Eu³⁺ ion” charge transfer states falls, which can promote the degradation of excitation energy. In naphthylcarboxylates investigated a range of the carboxylate triplet state energies from 19 150 to 20 600 cm⁻¹ was demonstrated in dependence on the type of the carboxylate anion. The interligand energy transfer from Phen to carboxylate lowest triplet state was revealed in complexes with Phen ligand. The effect of OH-group inserted in 1- or 3-position of 2-naphthoate ligand on the excitation energy transfer is also analyzed.     

Highly improved electroluminescence from double-layer devices based on a carbazole-functionalized europium<Superscript>3+</Superscript> complex

A novel europium complex Eu(TTA)₃(CPPO)₂ (1) (TTA=thenoyltrifluoroacetone, CPPO=9-[4-(diphenyl-phosphinoyl)-phenyl]-9H-carbazole) based on the phosphine oxide ligand with bipolar structure was used to fabricate double-layer devices. The strong hole injection and transport ability of 1 was proved. The luminance of 414 cd m⁻² was achieved with the device configuration ITO/Eu(TTA)₃(CPPO)₂(40 nm)/BCP (30 nm)/Mg:Ag (BCP = 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline), which is favorable among double-layer organic light emitting devices based on small molecular Eu³⁺ complexes. The maximum current efficiency of 2.44 cd A⁻¹ and external quantum efficiency of 1.55% demonstrate the potential application of 1 as a promising candidate for high-efficiency, simple-structure and pure red-emitting devices.     

Preparation, characterization, and luminescence properties of novel hybrid material containing europium(III) complex covalently bonded to MCM-41

In this paper, a novel luminescent organic-inorganic hybrid material containing covalently bonded ternary europium complex in mesoporous silica MCM-41 has been successfully prepared by co-condensation of tetrethoxysilane (TEOS) and the modified ligand 2-phenyl-1H-imidazo[4,5-f][1,10]phen-3-(triethoxysilyl)propylcarbamate (PIP-Si) in the presence of cetyltrimethylammonium bromide (CTAB) surfactant as template. PIP-Si containing 1,10-phenanthroline covalently grafted to 3-(triethoxysilyl)propyl isocyanate is used not only as a precursor but also as the second ligand for Eu(TTA)₃·2H₂O (TTA: 2-thenoyltrifluoroacetate) complex to prepare a novel functionalized mesoporous material. The resulted mesoporous composite materials, which demonstrate strong characteristic emission lines of Eu³⁺⁵D₀-⁷F_J (J=0, 1, 2, 3, 4), were characterized by Fourier transform infrared (FT-IR), small-angle X-ray diffraction, excited-state decay analysis. Emission intensity of the Eu(III) complex covalently linked to MCM-41 (Eu-MCM-41) increases with the increasing irradiation time, demonstrating better photostability compared with both pure Eu(III) complex and physically incorporated sample.     

Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)₂(NO₃)(TPPO)₂] (bis-TTA complex) and [Eu(TTA)₃(TPPO)₂] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA=2-thienoyltrifluoroacetone and TPPO=triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogravimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)₃(TPPO)₂] and [Gd(TTA)₂(NO₃)(TPPO)₂] complexes are associated to T→S₀ transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Ω_λ (λ=2 and 4), spontaneous emission rates (A_rad), luminescence lifetime (τ), emission quantum efficiency (η) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(III) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)₂(NO₃)(TPPO)₂] complexes are discussed in terms of ligand-to-metal energy transfer.     

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE³⁺=Eu³⁺, Gd³⁺ and Tb³⁺) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H₂O)₂], [RE(TLA)(H₂O)₄] and [RE(TMA)(H₂O)₆], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd³⁺-(BTC) complexes showed that the triplet states (T) of the BTC³⁻ anions have energy higher than the main emitting states of the Eu³⁺ (⁵D₀) and Tb³⁺ (⁵D₄), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Ω₂) of Eu³⁺-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited ⁵D₀ and ⁵D₄ levels of the Eu³⁺ and Tb³⁺ ions is discussed. The emission quantum efficiencies (η) of the ⁵D₀ emitting level of the Eu³⁺ ion have been also determined. In the case of the Tb³⁺ ion, the photoluminescence data show the high emission intensity of the characteristic transitions ⁵D₄→⁷F_J (J=0-6), indicating that the BTC ligands are good sensitizers. The RE³⁺-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials.     

Photosensitized luminescence of thermostable polynuclear Eu(III) complexes

Tetranuclear europium(III) complexes, [Eu₄(μ-O)(L₁)₁₀] (L₁=2-hydroxy-4-octyloxybenzophenone,1) and [Eu₄(μ-O)(L₂)₁₀] (L₂=2-hydroxy-4-dodecyloxybenzophenone,2) were synthesized by the reaction of lanthanide nitrates with L₁ or L₂ in the presence of triethylamine in methanol. The photosensitized emission bands of the both Eu(III) complexes in THF-d₈ were observed around 579, 590, 615, 653, and 699 nm by the excitation of the ligands at 380 nm, whereas the emission from the mononuclear complex 3 containing ethanol molecules was almost quenched. The emission efficiencies were determined to be 3.1±0.1% for 1 and 3.9±0.1% for 2, respectively. The differential scanning calorimetry (DSC) measurements demonstrated that the decomposition points of 1 and 2 were 309 °C and 320 °C, respectively, indicating high thermostability of these complexes compared to the mononuclear Eu(III) complex 3 (250 °C). New strategy for designing stable rare earth compounds giving strong emission would be emphasized by introducing polynuclear complexes. Polynuclear complexes should open a wide range of molecular design for photosensitized luminescence and thermal stability.     

Structural and luminescence studies of trivalent europium complexes with pentaethylene glycol and 18-crown-6 ligands in the presence of picrate anion

Two new isostructural complexes of europium picrate (Eu-Pic) with pentaethylene glycol (EO5) and 18-crown-6 (18C6) ligands formed complexes of molecular formula [Eu(Pic)₂(18C6)]⁺(Pic)⁻I and [Eu(Pic)₂(EO5)]⁺(Pic)⁻II have been isolated and characterised. Compound I showed 10-coordination number through six oxygen atoms from the 18C6 ligand and two bidentate picrate anions. Meanwhile, compound II exhibited 9-coordination number via six oxygen atoms from EO5 ligand, two oxygen atoms from a bidentate and one oxygen atom from monodentate picrate anions. Photoluminescence (PL) spectra of the solid-state europium complexes display sharp lines which are assigned to ⁵D₀→⁷F_0-4 and ⁵D₁→⁷F_1,2,4 transitions. No emission of polyether ligands is observed, indicating that the energy transfer from the polyether ligands to the Eu³⁺ ion is quite efficient. The PL spectra of [Eu(Pic)₂(OH₂)₆]⁺(Pic)⁻·6H₂O III, [Eu(NO₃)₃(OH₂)₃]·(18C6) IV, [Eu(NO₃)₃·6H₂O] V and Eu₂O₃VI are also observed. Compounds I-IV exhibited high Ω₂ intensity parameter values, namely 16.93, 10.23, 17.10 and 12.35 (in units of 10⁻²⁰ cm²), respectively. These relatively high values reflect the hypersensitive behaviour of the ⁵D₀→⁷F₂ transition and indicate that the Eu³⁺ ion is located in a highly polarisable chemical environment.     

Design, synthesis and characterization of a highly luminescent Eu-complex monomer featuring thenoyltrifluoroacetone and 5-acryloxyethoxymethyl-8-hydroxyquinoline

A multi-functional ligand, 5-acryloxyethoxymethyl-8-hydroxyquinoline (Hamq), was synthesized, which contained a polymerizable C=C double bond for the copolymerization with other vinyl monomers and acted as photon antenna able to transfer energy to Eu³⁺ ions effectively. The triplet state energy of Hamq was determined to be 22,370 cm⁻¹ via the phosphorescence spectra of Hamq and its gadolinium complex. The title complex monomer Eu(tta)₂(amq) was prepared by coordination reaction of Hamq with europium isopropoxide and 2-thenoyltrifluoroacetone (Htta) in dry organic solvents under argon atmosphere and characterized by elemental analysis and IR spectrum. The photophysical properties of the complex were studied in detail with UV-vis, luminescence spectra, luminescence lifetime and quantum yield. The complex exhibited nearly monochromatic red emission at 612 nm, a remarkable luminescence quantum yield at room temperature (30.6%) upon ligand excitation and a long ⁵D₀ lifetime (389 μs), which indicated that the ligand Hamq could sensitize the luminescence of Eu(III) ion efficiently in Eu(tta)₂(amq), resulting in a strong luminescence of its copolymer poly[MMA-co-Eu(TTA)₂(amq)] under UV excitation. The excellent luminescence properties of the complex made it not only a promising light-conversion molecular device but also an excellent luminescent monomer.     

A reddish orange-emitting stoichiometric phosphor K3Eu(PO4)2 for white light-emitting diodes

A series of Eu³⁺ activated K₃Y_1?xEu_x(PO₄)₂ phosphors were synthesized by the solid-state reaction method. The structures and photoluminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic K₃Y(PO₄)₂ or K₃Eu(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370–410 nm) light. The orange emission from transition ⁵D₀–⁷F₁ is dominant, and the peak value ratio of ⁵D₀–⁷F₁/⁵D₀–⁷F₂ is 1.44. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x=0.63, y=0.36), which is due to the ⁵D₀–⁷F_J transitions of Eu³⁺ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The absence of concentration quenching of Eu³⁺ was observed in K₃Y_1?xEu_x(PO₄)₂. K₃Eu(PO₄)₂ has potential application as a phosphor for white light-emitting diodes.     

Influences of compositions and ligands on photoluminescent properties of Eu(III) ions in composite europium complex/PMMA systems

Three kinds of europium complexes; Eu(phen)₂Cl₃(H₂O)₂, Eu(DN-bpy)phenCl₃(H₂O)₂ and Eu(DB-bpy)phenCl₃(H₂O)₂ (phen: 1,10-phenanthroline, DN-bpy: 4,4′-Dinonyl-2,2′-dipyridyl, DB-bpy: 4,4′-Di-tert-butyl-2,2′-dipyridyl) were prepared and then incorporated into polymethyl methacrylate (PMMA) matrix with different molar ratios of CO groups/Eu³⁺ ions. The final solid composites were formed by a self-assembly process among Eu³⁺ ion, the ligands and PMMA during the solvent evaporation process, and then the ligands re-coordinate to Eu(III). It was found that the ligands affect not only the emission properties of the pure complexes, but also the miscibility of the complexes and PMMA. More than one kind of symmetric sites of Eu³⁺ ions were formed in the composites due to the coordination of CO in PMMA to Eu³⁺ ions. The micro-environments of Eu(III) in the composites were changed with the compositions and the ligands, leading to the change in the crystalline structure, and consequently, the emission characteristics.     

A luminescent dinuclear Eu(III) complex based on 2,8-bis(4′,4′,4′,-trifluoro-1′,3′-dioxobutyl)-dibenzothiophene for light-emitting diodes

A dinuclear Eu (III) complex Eu₂(dbt)₃·4H₂O was synthesized, where H₂dbt was 2,8-bis(4′,4′,4′,-trifluoro-1′,3′-dioxobutyl)-dibenzothiophene. The complex emits the characteristic red luminescence of Eu³⁺ ion due to the ⁵D₀→⁷F_J(J=0-4) transitions under 395 nm-light excitation with a luminescent quantum efficiency of 17%. The complex is thermally stable up to 280 °C. It was found that the complex can be effectively excited by a 395 nm-emitting InGaN chip. Bright red light was obtained using the complex as light color-conversion material.     

Size-dependent microstructure and europium site preference influence fluorescent properties of Eu-doped Ca10(PO4)6(OH)2 nanocrystal

In this study, Eu³⁺-doped nanocrystalline Ca₁₀(PO₄)₆(OH)₂ (Ca_10−xEu_x(PO₄)₆(OH)₂) with different particle sizes have been prepared by the thermal decomposition of precursors. Size-dependent microstructure could be observed in nanocrystalline Ca_10−xEu_x(PO₄)₆(OH)₂. The lattices of Ca_10−xEu_x(PO₄)₆(OH)₂ nanocrystals were more distorted in comparison with the bulk, and the smaller the particle size, the more distorted the lattices. Room temperature photoluminescence showed europium site preference was also size-dependent, with the majority of Eu³⁺ ions occupying Ca(II) sites in the bulk, but more and more Eu³⁺ ions occupying Ca(I) sites in Ca_10−xEu_x(PO₄)₆(OH)₂ with decreasing particle size. Fluorescent properties of Ca_10−xEu_x(PO₄)₆(OH)₂ were considered to be influenced by both microstructure and site preference of Eu³⁺ ions. An abnormal strong intensity of ⁵D₀-⁷F₀ transition was observed in bulk and larger Ca_10−xEu_x(PO₄)₆(OH)₂ nanocrystals, but the relative intensities of ⁵D₀-⁷F₀ transition to ⁵D₀-⁷F_1,2,3,4 transition of Eu³⁺ became weaker as the particle sizes decreased. As the particle sizes became smaller, the ratios of the red emission transition (⁵D₀-⁷F₂) to the orange emission transition (⁵D₀-⁷F₁) (R/O values) first increased by comparing the bulk sample with 96 nm sample, and then decreased by comparing 96 nm sample to 57 nm sample. The quenching concentrations of Ca_10−xEu_x(PO₄)₆(OH)₂ samples increased with decreasing particle size. Possible mechanisms responsible for these phenomena were proposed. Since nanosized Ca_10−xEu_x(PO₄)₆(OH)₂ showed higher fluorescent intensities, higher R/O values and higher quenching concentrations, this material is considered to be a promising phosphor.     

Development of zeolite-derived novel aluminosilicate phosphors

In this research, zeolite-derived aluminosilicate phosphors were synthesized through the ion exchange route. Red light-emitting property of Eu³⁺-doped aluminosilicate phosphors were discussed from a view point of the Eu content, heat-treatment condition and the oxidation state of Eu ions. The crystalline phase of the host aluminosilicates could be successfully controlled as designed based on the published NaAlO₂–SiO₂ binary phase diagram. Orange-red emission peaks derived from the ⁵D₀→⁷F_j (j=0, 1, 2, 3, 4) transition of Eu³⁺ were observed around 590–700 nm, and 4f⁶5d→4f⁷ transition of Eu²⁺ was observed at around 400–500 nm. The relative intensity I(⁵D₀→⁷F₂) of the dominant emission peak at 612 nm increased consistently with the Eu content. The results of the XANES spectroscopy analysis revealed that Eu²⁺ ion in the 1400 °C as heat-treated host aluminosilicate were successfully converted to Eu³⁺ by the additional annealing at 1100 °C. The Eu contents and heat-treatment conditions were determined to exhibit the best performance as a red phosphor, which were 10 wt% and 1500 °C, respectively