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Several complexes and silica-based nanohybrids of rare-earth ions (Eu3+, Gd3+) have been synthesized from dimethyl 4-azidopyridine-2,6-dicarboxylate ( 4) following the Click chemistry approach. A complete spectroscopic study indicates that such compounds exhibit strong sensitization by the antenna effect from both UV and NIR excitations. The Gd3+-based materials show phosphorescence under ambient conditions, which originates from the lowest-energy intra-ligand triplets. Fine analysis of the NIR excitation spectra using time resolved photoluminescence spectroscopy (TRS) indicates that the spectral repartition of the triplet T1 state differs notably between the complexes and the NPs embedding the complexes. Moreover the dependence of Eu3+ luminescence vs. incident beam power in the NIR region diverges from pure quadratic dependence expected in the framework of the two-photon absorption process. The results are discussed considering the occurrence of a direct singlet-to-triplet optical absorption transition (S0→T1) upon NIR excitation. [ABSTRACT FROM AUTHOR]

This work deals with a red phosphor, Y3BO6:Eu3+, and its corresponding poly(N-vinylpyrrolidone) (PVP)/Y3BO6:Eu3+ luminescent composite film suitable for applications in the next generation of Hg-free lamps based on near ultraviolet (UV) light emitting diodes (LEDs). Well crystallized samples of Y3BO6 powders with the Eu3+ content up to 20 mol% were prepared by the Pechini method. After structural, morphological and optical characterization, the best doping rate of Eu3+ in the matrix was determined to be 15 mol%. This optimal powder, which is highly friable, was easily ground into fine particles and homogeneously dispersed into a PVP polymer solution to give rise to a polymer phosphor composite. Structural and optical features of the composite film have been studied and compared to those of a pristine PVP film and Y3BO6:Eu3+ powder. All the characterization (XRD, SAXS, luminescence…) proved that the red phosphor particles are well incorporated into the polymer composite film which exhibited the characteristic red emission of Eu3+ under UV light excitation. Furthermore, photostability of the polymer/phosphor composite film under UV-LED irradiation was evaluated from exposure to accelerated artificial photoageing at wavelengths above 300 nm. [ABSTRACT FROM AUTHOR]

This work focuses on the study of BaMgAl10O17:Eu2+ (BAM:Eu) nanophosphors prepared by a microwaveassisted combustion procedure and more especially on the polymer/BAM:Eu nanocomposite film suitable for optical devices such as solid-state-lighting. Powder presented a specific nanomorphology, highly friable and thus easily ground into fine particles. They were then homogeneously dispersed into a polymer solution (poly(N-vinylpyrrolidone) or PVP) to elaborate a polymer phosphor nanocomposite. The structural, morphological and optical features of the nanocomposite film have been studied and compared to those of a pristine PVP film and BAM:Eu powder. All the characterizations (XRD, SEM, SAXS, etc.) proved that the blue phosphor nanoparticles are well incorporated into the polymer nanocomposite film which exhibited the characteristic blue emission of Eu2+ under UV light excitation. Furthermore, the photostability of the polymer/phosphor nanocomposite film has been studied after exposure to accelerated artificial photoageing at wavelengths above 300 nm. [ABSTRACT FROM AUTHOR]

Solvothermal methods to synthesize cerium-doped YAG nanoparticles (YAG:Ce3+ NPs) generally require relatively long heating times (th≥ 1 h) and temperatures close to 300 °C. In this work, we report a rapid solvothermal synthesis (th = 5 min) leading to well-crystallized and highly monodisperse YAG:Ce3+ NPs of about 30 nm diameter by heating mixed yttrium, aluminium and cerium carbonate precursors in an autoclave at 300 °C using a 1,4-butylene glycol–water mixture as solvent. The as-prepared YAG:Ce3+ NPs showed a broad emission band in the green–yellow range having maximum intensity at 550 nm upon blue or UV excitation. The effect of heating time and Ce3+ concentration on structural, morphological and optical properties of YAG:Ce3+ NPs has been systematically studied by X-ray powder diffraction, transmission electron microscopy, FT-IR spectroscopy, energy dispersive spectroscopy and room temperature photoluminescence experiments. The combination of low Ce3+ doping concentration and short heating time plays a crucial role in the good optical properties of the obtained YAG:Ce3+ NPs. The particles hold good potential to be applied in solid-state lighting or used as coating for display system applications. [ABSTRACT FROM AUTHOR]

Abstract: From radiative transitions rates in praseodymium, neodymium, erbium, holmium and thulium ions doped LaAlO3 and measured emission decay times multiphonon nonradiative transitions rates W MNR have been calculated. Radiative transition rates were determined in the frame of Judd–Ofelt theory. The data obtained were plotted in the function of energy gap ΔE and fitted by exponential function W MNR =B·exp(−α ·ΔE), where B =1.02×109 and α =3.61×10−3. Fitting results show that multiphonon nonradiative transition rates are low comparing to other oxide crystals being similar to those of YAG. [Copyright &y& Elsevier]

Abstract: The excited state dynamics of the Pr3+ in oxide lattices is revisited in the light of the ‘virtual recharge’ model. The connection between the quenching of the blue-green emission from the 3P0 level and the formation of a Pr3+ to metal intervalence charge-transfer state (IVCTS) is discussed on the basis of new experimental evidences. Updated information is presented, concerning the energy position of the IVCTS in various materials and its relation with the host properties. Finally, the limits of the proposed model are outlined and the perspectives for future work are pointed out. [Copyright &y& Elsevier]

Abstract: Luminescence spectra of Pr3+ in 15 titanate and vanadate lattices have been measured under UV excitation. They are characterized by a dominant red luminescence assigned to transitions from the 1D2 level to the ground state. The quenching of the otherwise prominent blue luminescence from 3P0 state is ascribed to a relaxation pathway involving a low-lying Pr3+–M n+ (M n+ =Ti4+ or V5+) intervalence charge transfer (IVCT) state. Complete quenching of the 3P0 emission takes place when the IVCT bands are located in the 26500–28000cm−1 range and the shortest Pr3+–M n+ distances are in the 3.15–3.30Å range. [Copyright &y& Elsevier]

Abstract: Luminescent Tb3+ yttrium-based garnets powders have been prepared by the sol–gel route. Optical properties of samples have been studied. Excitation spectra have revealed several excitation bands between 200 and 500nm, which match very well with newly developed AlGaN-based deep-ultraviolet (DUV) or near-UV LEDs. Excitation profiles are dependent on the matrix formula. Emission spectral features studied upon different UV excitation wavelength have revealed that luminescence efficiency can be significantly improved by tuning the matrix composition. Thus, optical properties can be tuned to optimize the lighting source features, according to the kind of UV LEDs employed. [Copyright &y& Elsevier]

Abstract: Single crystals of Ba2NaNb5O15 (BNN) singly doped with Sm3+, Eu3+, Tb3+ or Dy3+ have been grown by means of the flux growth method. Their visible emission and excitation spectra and the decay profiles of the luminescence have been measured at room temperature. All spectral features are significantly inhomogeneously broadened in consequence of the structural disorder of the host and of the doping mechanisms. The analysis of the observed spectra allows formulating an hypothesis about the site occupancy of the active ions in the BNN lattice. [Copyright &y& Elsevier]

Abstract: Sol–gel synthesis of isostructural LiGdF4:Eu3+ and LiYF4:Er3+ crystallized powders is reported. Furthermore, LiGdF4:Eu3+ coatings were also prepared by dip- and spin-coating methods. In all cases, X-rays diffraction measurements were performed to check materials crystalline purity while infrared spectroscopy analyses showed that the organic groups are removed after annealing treatments at 550°C in F2 atmosphere. This result was emphasized by long radiative decay time of Er3+ ions in LiYF4 (τ =10.5ms) attributed to the absence of both organic residues and hydroxide ions. Laser induced emission spectra of LiGdF4:Eu3+ were recorded upon excitation in both 5D2 and 6P5/2 high lying levels of respectively Eu3+ and Gd3+ ions. Eventually fluorescence decays of rare earth ions were measured and compared in both cases. [Copyright &y& Elsevier]

Abstract: Sol–gel route has been successfully used to obtain pure LiYF4:Eu3+ powders for the first time to our best knowledge. Fluorine ions were introduced through trifluoroacetic acid as reacting agent which is decomposed under heating treatment and as a result leads to the formation of fluorides. Sintering under F2 reactive atmosphere was performed to prevent any oxidation and insure residual hydroxide elimination. The materials structure was analyzed by means of X-ray diffraction (XRD) while infrared spectroscopy (IR) was carried out to examine the presence of residual organic groups. Laser induced luminescence spectra as well as fluorescence decays of Eu3+ ions were recorded and compared to those of LiYF4:Eu3+ prepared by conventional solid state reaction. In both cases, the results are undoubtedly typical of Eu3+ emitting center embedded in a unique site of D2d symmetry. Nevertheless, the sol–gel derived samples exhibit 5D0 luminescence decays characterized by longer rise times upon 5D2 excitation as well as a larger 5D1/5D0 branching ratio at room temperature or 100K. [Copyright &y& Elsevier]

Sol–gel route has been successfully used to obtain pure Y3Al5O12 and Y3Al5O12:Eu3+ powders. The formation process, the structure as well as the microstructure of the materials were analyzed by means of X-ray diffraction (XRD), thermal analysis (TG–TDA), infrared spectroscopy (IR) and scanning electron microscopy (SEM). It has been shown that sol–gel derived YAG powders crystallize around 900 °C whereas a temperature much higher is necessary to obtain this compound by solid state synthesis (≈1500 °C). Laser induced luminescence spectra, as well as luminescence decays of Eu3+ ions show undoubtedly the spectral features of a Eu3+ emitting center embedded in a unique site of D2 symmetry. [Copyright &y& Elsevier]

Abstract: Sol–gel route has successfully been used to synthesize pure and Eu3+ doped polycrystalline samples of the GdP5O14 pentaphosphates. The as-prepared samples have structurally been characterized using X-ray diffraction. Optical properties in the vacuum ultraviolet (VUV) of Eu3+ activated GdP5O14 samples prepared either by sol–gel process or solid-state reaction were investigated at room temperature for comparison. In this GdP5O14 host matrix the P5O14 ultraphosphate groups were proved to exhibit an efficient absorption in the VUV range. The excitation spectra recorded in the VUV-UV spectral region from 120nm to 350nm have revealed the presence of Gd3+ 4f–5d interconfiguration transitions, Gd3+–O2− and Eu3+–O2− charge transfer states(CTS)in addition to intraconfiguration transitions of Gd3+ ions.Furthermore the Gd3+→Eu3+ energy transfer process was investigated and discussed in the framework of the multiphonon relaxation process. Besides, the GdP5O14:Eu3+ phosphor led to a strong red emission under 147/172nm excitation, so that it can be considered as a promising red phosphor for mercury-free lamps and plasma display panels applications. [Copyright &y& Elsevier]

Abstract: This work aims at achieving homogeneous luminescent films from Ce-doped yttrium aluminium garnet (YAG:Ce) phosphors dispersed in aqueous suspensions. Colloidal luminescent suspensions of YAG:Ce nanoparticles have been successfully prepared by a solvothermal process. Powder resulting from the dried as-synthesized suspension was submitted to different thermal treatments and a thorough study of nanoparticles aqueous suspensions has been carried out, for each thermal treatment. The influence of these treatments on the structural, morphological and optical properties of YAG:Ce nanopowders were studied by means of X-ray diffraction, infrared spectroscopy and transmission electron microscopy. Besides, particles size distribution and zeta potential of YAG:Ce aqueous suspensions in different pH conditions were investigated by dynamic light and electrophoretic light scatterings, respectively, in order to characterize suspensions stability. This study enabled us to optimize heat treatment and redispersion parameters in order to achieve very homogeneous luminescent films which can be used for display or mood lighting. [Copyright &y& Elsevier]

Barium titanate nanocrystallites were synthesized by a hydrothermal technique from barium chloride and tetrabutyl titanate. Single-crystalline cubic perovskite BaTiO3 consisting of spherical particles with diameters ranging from 10 to 30 nm was easily achieved by this route. In order to study the influence of the synthesis process on the morphology and the optical properties, barium titanate was also prepared by a solid-state reaction. In this case, only the tetragonal phase which crystallizes above 900°was observed. High-temperature X-ray diffraction measurements were performed to investigate the crystallization temperatures as well as the particle sizes via the Scherrer formula. The lattice vibrations were evidenced by infrared spectroscopy. Eu3+ was used as a structural probe, and the luminescence properties recorded from BaTiO3:Eu3+ and elaborated by a solid-state reaction and hydrothermal process were compared. The reddish emission of the europium is increased by the nanometric particles. [ABSTRACT FROM AUTHOR]

Abstract: The citric route was employed for synthesis of the pure phase Ca9Al(PO4)7:Eu3+ (CAlP:Eu3+) powders as an attractive alternative to the solid state reaction (no need of multistep and long thermal treatment). Structural properties of the final product were studied by means of X-ray diffraction as well as Rietveld refinement was conducted in order to calculate the cell parameters. The thermal behavior of the emission was studied using excitation line well matched with the 7F0 → 5D4 absorption band covering broad range of temperature. Activation energy was estimated to be equal to 10,550cm−1. The thermal behavior of the Eu3+ luminescence in CAlP crystal lattice shown that the almost 80% of intensity is kept up to 430K. [Copyright &y& Elsevier]

Abstract: The luminescence properties of CaMoO4:Pr3+ have been investigated in different experimental conditions in order to obtain information on the excitation and de-excitation pathways of this system. The structure of the emission spectrum depends on different factors: excitation conditions, doping level, temperature, etc. In addition, measurements carried out on single crystals and on micro- or nano-crystalline powders obtained by solid state reaction and sol–gel method have revealed that the morphology of the sample, and then the concentration of the lattice defects, strongly influences the excitation mechanism. These effects have been analysed in the light of available models and a general scheme accounting for the experimental observations has been proposed. [Copyright &y& Elsevier]

Abstract: Blue-emitting Eu2+-doped barium magnesium aluminate (BaMgAl10O17:Eu2+) for advanced displays and lighting devices was prepared by a microwave induced solution combustion synthesis using urea as combustion fuel and nitrates as oxidizer. Purity control of as-synthesized blue phosphor particles was undertaken by modifying the fuel to oxidizer molar ratio. X-ray diffraction, scanning electron microscopy and photoluminescence were used to investigate powders crystallinity, particles size, morphology and luminescent properties, respectively. Fuel-rich urea reactions preferentially lead to pure phases compared to the powders synthesized with a stoichiometric fuel to oxidizer ratio. In both cases, we produce a nearly pure well-crystallized and nanostructured BaMgAl10O17:Eu2+. Photoluminescence measurements exhibit the characteristic blue emission of Eu2+ under UV light excitation however a weak red emission associated to Eu3+ is also detected. [Copyright &y& Elsevier]