Flexible polyarylene ether nitrile containing pendant carboxyl groups/Eu(III) fluorescent films with high thermal stability and mechanical strength

A series of flexible and transparent polyarylene ether nitrile with pendant carboxyl groups/Eu(III) fluorescent films were successfully prepared, and characterized by scanning electron microscopy, energy-dispersive spectroscopy, thermogravimetric analysis, tensile test, ultraviolet–visible absorption and fluorescence spectroscopy. The results showed that the films possess high thermal stability (5% weight loss temperatures over 425 °C) and high mechanical strength (tensile strengths exceeding 90 MPa). Furthermore, all the films exhibit a relatively high transmittance in the visible region, and also show an excellent macroscopic flexibility, so that they can be easily bent and curled. This is mainly attributed to the superior performance of the polymer matrix. The photoluminescence results indicated that the films emit an intense red light at 617 nm under ultraviolet excitation, which is attributed to the ⁵D₀ → ⁷F₂ transitions of Eu(III) ions.     

Photoluminescence properties of Y3Al5O12:Eu nanocrystallites prepared by co-precipitation method using a mixed precipitator of NH4HCO3 and NH3·H2O

Europium-doped yttrium aluminum garnet (Y₃Al₅O₁₂:Eu, YAG:Eu) nanocrystallites were prepared by calcining the precursors obtained via a co-precipitation method using a mixed solution of NH₄HCO₃ and NH₃·H₂O as the precipitator. The results of XRD, FTIR and thermal analysis showed that phase-pure YAG:Eu without any other phases was obtained at 900 °C. TEM results indicated that the particle sizes are 50–100 nm. YAG:Eu nanocrystallites showed four emission bands ascribed to ⁵D₀ → ⁷F₁ transition (592 and 597 nm) and ⁵D₀ → ⁷F₂ transition (611 and 633 nm) of Eu³⁺, respectively. The intensity of the magnetic dipole transition (⁵D₀ → ⁷F₁) is stronger than that of the electric dipole transition (⁵D₀ → ⁷F₂). The influence of the precipitators with different molar ratios of NH₄HCO₃ to NH₃·H₂O on the thermal properties of the as-prepared precursors and luminescent properties of the resulting YAG:Eu nanocrystallites was also investigated.     

Synthesis,structural characterization and photophysical properties of highly photoluminescent crystals of Eu(III), Tb(III) and Dy(III) with 2,5-thiophenedicarboxylate

Lanthanide compounds of general formula [Ln₂(2,5-tdc)₃(dmf)₂(H₂O)₂]·2dmf·H₂O (Ln = Eu(III) (1), Tb(III) (2), Gd(III) (3) and Dy(III) (4), dmf = N,N′-dimethylformamide and 2,5-tdc²⁻ = 2,5-thiophedicarboxylate anion) were synthesized and characterized by elemental analysis, X-ray powder diffraction patterns, thermogravimetric analysis and infrared spectroscopy. Phosphorescence data of Gd(III) complex showed that the triplet states (T₁) of 2,5-tdc²⁻ ligand have higher energy than the main emitting states of Eu(III), Tb(III) and Dy(III), indicating that 2,5-tdc²⁻ ligand can act as intramolecular energy donor for these metal ions. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer. The high value of experimental intensity parameter Ω₂ for the Eu(III) complex indicate that the europium ion is in a highly polarizable chemical environment. The emission quantum efficiency (η) of the ⁵D₀ emitting level of Eu(III) was also determined. The complexes act as possible light conversion molecular devices (LCMDs).     

Synthesis and luminescent properties of SrZnO2:Eu3+,M+ (M = Li,Na, K) phosphor

In this paper, a series of novel luminescent materials, SrZnO₂:Eu³⁺,M⁺ (M = Li, Na, K) have been synthesized by conventional solid-state reaction. X-ray diffraction (XRD) patterns and photoluminescence (PL) spectra were carried out to characterize their structural and luminescent properties. It was found that under ultraviolet excitation with a wavelength of 301 nm, SrZnO₂:Eu³⁺ gives a red luminescence that was attributed to the transitions from ⁵D₀ excited states to ⁷F_J (J = 0–4) ground states of Eu³⁺ ions. The feature and the high intensity of hypersensitive transition ⁵D₀ → ⁷F₂ indicate that Eu³⁺ prefers to occupy a low symmetry site. The incorporation of alkali metal ions greatly enhanced the luminescence intensity and slightly changed the excitation and emission peak position, probably due to the influence of the coordination conditions for Eu³⁺ ions.     

In situ synthesis and luminescence characteristics of complexes of europium(III) with 4,6-diacetylresorcinol

The complexes of europium(III) with 4,6-diacetylresorcinol (H₂DAR) and a co-ligand (phen, bpy or 2,2′-bipyridine N,N′-dioxide (2,2′-bpyO₂)) were in situ synthesized in silica matrix via a two-step gel process. The formation of complexes in silica gel was confirmed by the luminescence excitation spectra. The silica gels that contain in situ synthesized europium complexes exhibit the characteristic emission bands of the Eu(III). The results show that there are two ways to enhance the emission intensity of the Eu(III): (i) synthesize the complex in silica matrix and (ii) synthesize the complex with a co-ligand, which coordinates with Eu(III) in the composite system and can efficiently transfer the energy from 4,6-diacetylresorcinol to the Eu(III). The order of the luminescence intensities of the complexes is: Eu₂(DAR)₃(phen)₂-(sol–gel) > Eu₂(DAR)₃(2,2′-bpyO₂)₂-(sol–gel) > Eu₂(DAR)₃ (bpy)₂-(sol–gel) > Eu₂(DAR)₃-(sol–gel) > pure Eu₂(DAR)₃·4H₂O.     

Synthesis and two-color emission properties of BaGd2(MoO4)4:Eu3+,Er3+,Yb3+ phosphors

Eu³⁺, Er³⁺ and Yb³⁺ co-doped BaGd₂(MoO₄)₄ two-color emission phosphor was synthesized by the high temperature solid-state method. The structure of the sample was characterized by XRD, and its luminescence properties were investigated in detail. Under the excitation of 395 nm ultraviolet light, the BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ phosphor emitted an intense red light at 595 and 614 nm, which can be attributed to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺, respectively. The phosphor will also show bright green light under 980 nm infrared light excitation. The green emission peaks centred at 529 and 552 nm, were attributed to ⁴H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺, respectively. It indicated that the two-color emission can be achieved from the same BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ host system based on the different pumping source, 395 nm UV light and 980 nm infrared light, respectively. The obtained results showed that this kind of phosphor may be potential in the field of multi-color fluorescence imaging and anti-counterfeiting.     

Variation of the photoluminescence and vacuum ultraviolet excitation characteristics of BaZr(BO3)2:Eu3+ by the incorporation of Al3+, La3+, or Y3+ into the lattice

The photoluminescence (PL) and vacuum ultraviolet (VUV) excitation properties are studied for the BaZr(BO₃)₂:Eu³⁺ phosphor with incorporating the Al³⁺, La³⁺, or Y³⁺ ion into the lattice. The excitation spectrum shows an absorption band in the VUV region with the band-edge at 200 nm and a very weak charge transfer band of Eu³⁺ at about 226 nm. The luminescence spectrum shows a strong emission at 615 nm (⁵D₀ → ⁷F₂ transition) and weak emission at 594 nm (⁵D₀ → ⁷F₁ transition) in BaZr(BO₃)₂:Eu³⁺, with a good red color purity. The PL intensity is increased by incorporating Al³⁺ into the BaZr(BO₃)₂ lattice. The PL intensity has also increased by incorporating La³⁺ into the lattice, however, the red color purity has deteriorated because of the increased centrosymmetric nature of the site. With the incorporation of Y³⁺ into the BaZr(BO₃)₂ lattice, the PL characteristics of the Eu³⁺ activator resembles that in the YBO₃ lattices. The intensity of the red PL for the Eu³⁺ activator is the highest with good color purity for BaZr(BO₃)₂:Eu³⁺ incorporated with both Al³⁺ (10%) and La³⁺ (0.5%).     

Structural and photophysical properties of lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide

Lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide (HPMSP) as new sensitizers of visible luminescence were obtained. The series of stable lanthanide complexes Na[Ln(PMSP)₄], where Ln = Eu³⁺, Gd³⁺, Tb³⁺ were characterized by X-ray diffraction, IR, absorption, emission, and excitation spectra at 295 and 77 K as well as luminescence decay times and intrinsic emission quantum yields. The Tb complex, exhibiting relatively efficient ligand-to-metal energy transfer and strong metal-centred emission, is a promising candidate for effective UV-to-visible energy converters. Temperature dependent quenching of sensitized ⁵D₀ europium emission and presence of ⁵D₁ emission are discussed.     

Spectroscopic investigations on Eu3+ ions in Li–K–Zn fluorotellurite glasses

Eu³⁺ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO₂ + 10Li₂O + 10K₂O + 10ZnF₂ + xEu₂O₃, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from ⁷F₀ and ⁷F₁ levels of the Eu³⁺-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (⁵D₀ → ⁷F_0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu³⁺ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of ⁵D₂ level of the Eu³⁺ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of ⁵D₀ level of Eu³⁺ ions in Li–K–Zn fluorotellurite glass.     

Effect of the europium doping on the structural and luminescent properties of yttrium aluminum garnet

Europium activated yttrium aluminate (YAG:Eu) phosphors were synthesized using urea by wet chemical synthesis route. The luminescent behavior and the microstructural changes are monitored, depending on the amount of europium. The luminescent spectra of YAG:Eu phosphors possess four major emission bands in the range of 570–700 nm with maxima situated at 592 nm 598 nm, 611 nm and 631 nm. The intensity ratio between the 611 nm band as red component (⁵D₀ → ⁷F₂) and 592 nm band as orange component (⁵D₀ → ⁷F₁) is discussed, in order to obtain information about the chemical surroundings of the luminescent centers and their symmetry. X-ray diffraction showed that the main crystalline phase of the phosphors is yttrium aluminum garnet Y₃Al₅O₁₂ with cubic structure. Monoclinic Y₄Al₂O₉ phase was also found as impurity. The effect of the europium content on the microstructural parameters is revealed. The luminescent characteristics depend strongly on the structural purity, activator concentration and incorporation of europium ions in the host lattice. Additional investigations as FT-IR, BET, ICP-OES were performed for a better understanding of the luminescent and structural characteristics of YAG:Eu phosphor.     

Optical properties of sol–gel derived Sr2SiO4:Dy3+ – Photo and thermally stimulated luminescence

Trivalent dysprosium-doped strontium silicate (Sr₂SiO₄) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600 °C for formation of a single phase sample. The material was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), photoluminescence (PL), and thermally stimulated luminescence (TSL). The luminescence study revealed strong ⁴F_9/2 → ⁶H_13/2 transition at 577 nm (yellow), strong ⁴F_9/2 → ⁶H_15/2 transition at 482 nm (blue) and weak ⁴F_9/2 → ⁶H_11/2 transition at 677 nm (red), when excited by 250 nm (Charge transfer band, CTB) or 352 nm (f–f band). The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Dy³⁺ ions was evaluated based on which, the quenching mechanism was verified to be a multipole–multipole interaction. The thermally stimulated luminescence studies of Sr₂SiO₄:Dy³⁺ sample showed main TSL glow peak at 413 K. The trap parameters namely activation energy (E), order of kinetics (b), and frequency factor (s) for this peak were determined using glow curve shape method.     

Formation and spectral probing of transparent oxyfluoride glass-ceramics containing (Eu2+, Eu3+:BaGdF5) nano-crystals

In the present study, we report the formation of transparent glass-ceramics containing BaGdF₅ nanocrystals under optimum ceramization of SiO₂–BaF₂–K₂O–Sb₂O₃–GdF₃–Eu₂O₃ based oxyfluoride glass and the energy transfer mechanisms in Eu²⁺ → Eu³⁺ and Gd³⁺ → Eu³⁺ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu³⁺ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature (T_g), the crystallization onset temperature (T_x), and crystallization peak temperature (T_p) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF₅ phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5–15 nm in size. The emission transitions from the higher excited sates (⁵D_J, J = 1, 2, and 3) as well as lowered asymmetry ratio of the ⁵D₀ → ⁷F₂ transition (forced electric dipole transition) to that of the ⁵D₀ → ⁷F₁ transition (magnetic dipole) of Eu³⁺ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu³⁺ ions into the cubic BaGdF₅ nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu²⁺ ions and Gd³⁺ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu³⁺ by monitoring emission at 614 nm indicated energy transfer from (Eu²⁺ → Eu³⁺) and (Gd³⁺ → Eu³⁺) in both glass and glass-ceramics samples.     

Study of the line intensity in the optical and magnetooptical spectra in holmium-containing paramagnetic garnets

Studies of line intensity in the optical and magneto-optical spectra in the holmium-containing paramagnetic garnet Ho³⁺:YAG were carried out within the visible spectrum at T = 85 K. Detailed investigation of the magnetic circularly polarized luminescence spectra at 85 and 300 K on ⁵S₂ → ⁵I₈ emission transition in Ho³⁺:YAG was carried out. A quasi-doublet state in the energy spectrum of the Ho³⁺ ions was observed, characterized by a significant magneto-optical activity, which is caused by a large Zeeman splitting of the quasi-doublet. The measurement of the magnetic circular polarized luminescence spectrum carried out within one of the emission lines of the luminescence band ⁵S₂ → ⁵I₈ in Ho³⁺:YAG at 85 K shows significant magneto-optical effects of the intensity change of the emitted light, compared to that measured for the other emission lines in the same luminescent band.     

Luminescence of Sm2+ in strontium haloborates

The luminescence properties of Sm²⁺ in Sr₂B₅O₉R (R=Cl, Br) have been studied and compared with those in SrB₄O₇. In the range from 80 to 300 K the emission of Sm²⁺ in Sr₂B₅O₉R is predominantly due to the 4f⁵5d → 4f⁶ transition, while SrB₄O₇ : Sm²⁺ shows a very efficient emission of the 4f⁶ → 4f⁶ type. Differences in the luminescence of Sm²⁺ in the strontium haloborates and tetraborate are discussed.     

Structure and luminescence properties of Ba3WO6:Eu3+ nanowire phosphors obtained by conventional solid-state reaction method

For the first time, novel Ba_3−xWO₆:xEu³⁺ (x = 0.01, 0.03, 0.05, 0.08, 0.1) nanowire phosphors were synthesized by the conventional solid state method. The X-ray pattern indicates that Ba₃WO₆ belongs to the cubic system with space group Fm-3m. The photoluminescence (PL) spectra demonstrate that the phosphors emit strong red light centered at 595 nm corresponding to ⁵D₀ → ⁷F₁ transition of Eu³⁺ ion under CT band excitation. The position of charge transfer (CT) band of Ba_2.95WO₆:0.05Eu³⁺ shifts to a lower energy region (red shift) with the increase of annealing temperature. The co-doped effect of alkali-metal ions (Li⁺, Na⁺, and K⁺) on the luminescence behavior of Ba₃WO₆:Eu³⁺ has been discussed in this paper. The luminescence properties suggest that the Ba₃WO₆:Eu³⁺ phosphor may be a promising candidate in solid-state lighting applications.     

Novel highly luminescent europium dinitrosalicylates

A series of lanthanide dinitrosalicylates M₃Ln(3,5-NO₂-Sal)₃ · nH₂O (Ln = Eu, Gd; M = Li, Na, K, Cs) was synthesized. It was found that the luminescence efficiency of some M₃Eu(3,5-NO₂-Sal)₃ · nH₂O compounds was near to the high efficiency of europium dibenzoylmethanate with 1,10-phenanthroline, Eu(DBM)₃ · Phen. The luminescence excitation spectra, electron-vibrational luminescence spectra, and vibrational IR spectra were investigated. The energy of the lowest excited triplet state of the ligand was obtained from phosphorescence spectra of M₃Gd(3,5-NO₂-Sal)₃ · nH₂O, M(3,5-NO₂-HSal) · nH₂O, and M₂(3,5-NO₂-Sal) · nH₂O. The details of the structure of compounds were discussed. The influence of different M-cations on the Eu³⁺ luminescence efficiency and on the processes of excitation energy transfer to a Eu³⁺ ion was analyzed. The presence of large alkali metal cations in lanthanide dinitrosalicylates and an increase in the temperature weaken the network of hydrogen bonds and, to some extent, the “ligand–metal” bonds. This is a cause of a long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu³⁺ excitation spectra arising at inclusion of Cs⁺ instead of Li⁺ cations in the crystal lattice and at the heating of compounds. A change of the energies of ligand electronic states at substitution of Li⁺ and Na⁺ for Cs⁺ can give a tenfold enhancement of the Eu³⁺ luminescence efficiency at 300 K.     

Synthesis and photoluminescence study of La1.8Eu0.2O3 coating on nanometric α-Al2O3

In this work the La_1.8Eu_0.2O₃ coating on nanometric alpha-alumina, α-Al₂O₃@La_1.8Eu_0.2O₃, was prepared for the first time by a soft chemical method. The powder was heat-treated at 100, 400, 800 and 1200 °C for 2 h. X-ray powder diffraction patterns (XRD), transmission electronic microscopy (TEM), emission and excitation spectra, as well as Eu³⁺ lifetime were used to characterize the material and to follow the changes in structure as the heating temperature increases. The Eu³⁺ luminescence data revealed the characteristic transitions ⁵D₀ → ⁷F_J (J = 0, 1 and 3) of Eu³⁺ at around 580, 591 and 613 nm, respectively, when the powders were excited by 393 nm. The red color of the samples changed to yellow when the powder was annealed at 1200 °C. The decrease in the (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) ratio from around 5.0 for samples heated at lower temperatures to 3.1 for samples annealed at 1200 °C is consistent with a higher symmetry of the Eu³⁺ at higher temperature. The excitation spectra of the samples also confirms this change by the presence of a more intense and broad band at around 317 nm, instead of the presence of the characteristic peak at 393 nm, which corresponds to the ⁷F₀ → ⁵L₆ transition of the Eu³⁺. The lifetimes of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ for the samples heat-treated at 100, 400, 800 and 1200 °C was evaluated as 0.57, 0.72, 0.43 and 0.31 ms, respectively.     

Nature of intrinsic and impure luminescence of MAlP2O7 crystals

The results of the photoluminescence (PL) investigation of pure and chromium-doped MAlP₂O₇ (M = Na, K, Cs) compounds are presented. The spectra of the intrinsic luminescence of MAlP₂O₇ crystals consist of a separated UV band at a peak position near 330 nm and a complex wide band which covers the region of visible light up to 750 nm at excitation by VUV synchrotron radiation. The “red” band in 600–1000 nm diapason appears in the PL spectra of crystals doped with chromium ions. The effect of the temperature on the structure, the peak positions and intensities of the luminescence bands was studied. An assumption about the nature of the intrinsic PL was made. The “red” luminescence was considered as a result of the ⁴Т₂ → ⁴А₂ radiation transitions in the impurity Cr³⁺ ions located in the intermediate crystal field.     

Enhanced photoluminescence and electrical properties of 0-3 type ZnO/Bi3.6Eu0.4Ti3O12 nanocomposite thin films

0-3 type ZnO/Bi_3.6Eu_0.4Ti₃O₁₂ (BEuT) nanocomposite films with ZnO nanopowders in BEuT host were prepared by chemical solution deposition. The effects of ZnO content on the structure, photoluminescence, and electrical properties of the films were investigated. The ZnO/BEuT molar ratio strongly affected the grain size and growth orientation of BEuT, dielectric and ferroelectric properties, as well as emission intensity. The nanocomposite films showed strong red emission peaks due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions. Good electrical properties with high dielectric constant of 480 (at 1 kHz) and large remanent polarization (2P_r) of 32 μC/cm² were obtained for the nanocomposite films having a ZnO/BEuT molar ratio of 1:2. The mechanisms for enhanced photoluminescence and electric properties were discussed. The results suggest that the nanocomposite thin films are promising candidate materials for multifunctional optoelectronic devices.     

Yellow lighting upconversion from Yb3+/Ho3+ co-doped CaMoO4

Yellow upconversion (UC) luminescence is observed in Ho³⁺/Yb³⁺ co-doped CaMoO₄ synthesized by complex citrate-gel method. Under 980 nm excitation, Ho³⁺/Yb³⁺ co-doped CaMoO₄ exhibited yellow emission based on green emission near 543 nm generated by ⁴F₄, ⁵S₂ → ⁵I8 transition and strong red emission around 656 nm generated by ⁵F₅ → ⁵I₈ transition, which are assigned to the intra 4f transitions of Ho³⁺ ions. The optimum doping concentration of Ho³⁺ and Yb³⁺ was investigated for highest upconversion luminescence. Based on pump power dependence, upconversion mechanism of Ho³⁺/Yb³⁺ co-doped CaMoO₄ was studied in detail.