Photoluminescent properties of Eu3+‐Eu2+ activated MAl2SixO2x + 4 (M = Mg,Ca, Sr,Ba) phosphors prepared in air

In this paper, MAl₂Si_xO_2x+4:Eu²⁺/Eu³⁺ (Eu²⁺ + Eu³⁺ = 2%, molar ratio; M = Mg, Ca, Sr, Ba; x = 0, 0.5, 1, 1.5, 2) phosphors with different SiO₂ concentrations (the ratio of SiO₂ to MAl₂O₄ is n%, n = 0, 50, 100, 150, 200, respectively) were prepared by high‐temperature solid‐state reaction under atmospheric air conditions. Their structures and photoluminescent properties were systematically researched. The results indicate that Eu³⁺ ions have been reduced and Eu²⁺ ions are obtained in air through the self‐reduction mechanism. The alkaline earth metal ions and doping SiO₂ strongly affect the crystalline phase and photoluminescent properties of samples, including microstructures, relative intensity of Eu²⁺ to Eu³⁺, location of emission lines/bands. It is interesting and important that the emission color and intensities of europium‐doped various phosphors which consist of aluminosilicate matrices prepared under atmospheric air conditions could be modulated by changing the kinds of alkaline earth metal and the content of SiO₂.     

Tunable luminescence properties and energy transfer in LaAl11O18:Eu,Tb phosphor

Eu²⁺ and Tb³⁺ singly doped and co‐doped LaAl₁₁O₁₈ phosphors were prepared by a combustion method using urea as a fuel. The phase structure and photoluminescence (PL) properties of the prepared phosphors were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence excitation and emission spectra. When the content of Eu²⁺ was fixed at 0.01, the emission chromaticity coordinates could be adjusted from blue to green region by tuning the contents of Tb³⁺ ions from 0.01 to 0.03 through an energy transfer (ET) process. The fluorescence data collected from the samples with different contents of Tb³⁺ into LaAl₁₁O₁₈: Eu, show the enhanced green emission at 545 nm associated with ⁵D₄ –⁷F₅ transitions of Tb³⁺. The enhancement was attributed to ET from Eu²⁺ to Tb³⁺, and therefore Eu²⁺ ion acts as a sensitizer (an energy donor) while Tb³⁺ ion as an activator. The ET from Eu²⁺ to Tb³⁺ is performed through dipole–dipole interaction. The ET efficiency and critical distance were also calculated. The present Eu²⁺–Tb³⁺ co‐doped LaAl₁₁O₁₈ phosphor will have potential application for UV convertible white light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

A promising RVO4:Eu3+,Li+@SiO2 (R = Gd,Y and Gd/Y) red‐emitting phosphor with improved luminescence (cd/m2) and colour purity for optical display applications

Red emission intensity was optimized in three stages, by investigating the effects of: (i) host composition (Gd, Y and Gd/Y), (ii) codoping Li⁺ as a sensitizer and, finally, (iii) with a SiO₂ shell coating as a protecting layer. Lanthanide vanadate powder phosphors were synthesized using a modified colloidal precipitation technique. The effects of SiO₂ coating on phosphor particles were characterized using scanning electron microscopy (SEM)‐EDAX, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and photoluminescence (PL) measurements. An improvement in the PL intensity on Li codoping was due to improved crystallinity, which led to higher oscillating strengths for the optical transitions, and also a lowering of the inversion symmetry of Eu³⁺ ions. Red emission intensity due to ⁵D₀ → ⁵D₂ transition of the phosphor Y_0.94VO₄:Eu³⁺_0.05,Li⁺_0.01 was enhanced by 22.28% compared with Y_0.95VO₄:Eu³⁺_0.05, and was further improved by 58.73% with SiO₂ coating. The luminescence intensity (I) and colour coordinates (x, y) of the optimized phosphor Y_0.94VO₄:Eu³⁺_0.05,Li⁺_0.01@SiO₂, where I = 13.07 cd/m² and (x = 0.6721, y = 0.3240), were compared with values for a commercial red phosphor (Y₂O₂S:Eu³⁺), where I = 27 cd/m² and (x = 0.6522, y = 0.3437). The measured colour coordinates are superior to those of the commercial red phosphor, and moreover, match well with standard NTSC values (x = 0.67, y = 0.33). Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence properties of neodymium,samarium, and europium niobate and tantalate thin films

Thin films of lanthanide orthoniobate LnNbO₄ (LnNO) and orthotantalate LnTaO₄ (LnTO), (Ln = Nd, Sm, Eu) were fabricated using the sol–gel method with subsequent spin-coating on the PbZrO₃/Al₂O₃ substrate and annealing at 1000°C. X-ray diffraction patterns showed monoclinic M-LnNbO₄ or M´-LnTaO₄, which coexists with the orthorhombic or tetragonal phase. X-ray photoelectron spectroscopy demonstrated the presence of Nd³⁺, Sm³⁺/Sm²⁺ and Eu³⁺/Eu²⁺ ions. The luminescence properties of polymorphic films were investigated. Excitation spectra of PbZrO₃ interlayer represented broad bands at 410 and 550 nm that were assigned to charge transfer bands (CTB). In all films, the CTB broad band at ~275 nm related to charge transfer transition of Ln³⁺→O²⁻ and NbO₄³⁻ or TaO₄³⁻ groups. In excitation spectra, ⁴I_9/2→⁴G_5/2 (Nd³⁺), ⁶H_5/2→⁶P_3/2 (Sm³⁺) and ⁷F₀→⁵L₆ (Eu³⁺) transitions (at 585, 402 and 395 nm), respectively were found to be more intense than any other Ln³⁺ transition. The emission spectra showed narrow and intense bands at 1065, 600, and 614 nm that were ascribed to Nd³⁺, Sm³⁺, and Eu³⁺ 4f–f intraconfigurational transitions ⁴F_3/2→⁴I_11/2, ⁴G_5/2→⁶H_7/2, and ⁵D₀→⁷F₂, respectively. The excellent luminescence properties of films make them new potential groups for visible and/or near-infrared applications such as sensors and imaging equipment.     

Size‐tailored synthesis and luminescent properties of three‐dimensional BaMoO4, BaMoO4:Eu3+ micron‐octahedrons and micron‐flowers via sonochemical route

Almost monodisperse three‐dimensional (3D) BaMoO_4, BaMoO₄:Eu³⁺ micron‐octahedrons and micron‐flowers were successfully prepared via a large‐scale and facile sonochemical route without using any catalysts or templates. X‐Ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy dispersion X‐ray (EDS), Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopy were employed to characterize the as‐obtained products. It was found that size modulation could be easily realized by changing the concentrations of reactants and the pH value of precursors. The formation mechanism for micron‐octahedrons and micron‐flowers was proposed on the basis of time‐dependent experiments. Using excitation wavelengths of 396 or 466 nm for BaMoO₄:Eu³⁺ phosphors, an intense emission line at 614 nm was observed. These phosphors might be promising components with possible application in the fields of near UV‐ and blue‐excited white light‐emitting diodes. Simultaneously, this novel and efficient pathway could open new opportunities for further investigating the properties of molybdate materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural,morphological and steady state photoluminescence spectroscopy studies of red Eu3+‐doped Y2O3 nanophosphors prepared by the sol‐gel method

Europium trivalent (Eu³⁺)‐doped Y₂O₃ nanopowders of different concentrations (0.5, 2.5, 5 or 7 at.%) were synthesized by the sol‐gel method, at different pH values (pH 2, 5 or 8) and annealing temperatures (600°C, 800°C or 1000°C). The nanopowders samples were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared spectroscopy (FT‐IR) and steady state photoluminescence spectroscopy. The effect of pH of solution and annealing temperatures on structural, morphological and photoluminescence properties of Eu³⁺‐doped Y₂O₃ were studied and are discussed. It was found that the average crystallite size of the nanopowders increased with increasing pH and annealing temperature values. The Y₂O₃:Eu³⁺ material presented different morphology and its evolution depended on the pH value and the annealing temperature. Activation energies at different pH values were determined and are discussed. Under ultraviolet (UV) light excitation, Y₂O₃:Eu³⁺ showed narrow emission peaks corresponding to the ⁵D_0–⁷F_J (J = 0, 1, 2 and 3) transitions of the Eu³⁺ ion, with the most intense red emission at 611 assigned to forced electric dipole ⁵D₀→⁷F₂. The emission intensity became more intense with increasing annealing temperature and pH values, related to the improvement of crystalline quality. For the 1000°C annealing temperature, the emission intensity presented a maximum at pH 5 related to the uniform cubic‐shaped particles. It was found that for lower annealing temperatures (small crystallite size) the CTB (charge transfer band) position presented a red shift. Copyright © 2015 John Wiley & Sons, Ltd.     

稀土元素铕和钇对紫叶酢浆草试管苗生长的影响

在MS培养基中添加不同浓度的稀土元素铕(Eu)、钇(Y),研究Eu、Y对紫叶酢浆草试管苗生长的影响。结果表明,适宜浓度的Eu或Y能够促进紫叶酢浆草试管苗的生长和分化,但高浓度的Eu或Y则抑制紫叶酢浆草试管苗生长。     

The sensitive determination of nucleic acids using a fluorescence-quenching method.

Experiments indicated that nucleic acids can quench the fluorescence of the Eu3+ -2-thenoyltrifluoroacetone (TTA)-1,10-phenanthroline (Phen) system. Based on this, a sensitive method for the determination of nucleic acids was proposed. The experiments indicated that under the optimum conditions, the quenched fluorescence intensity was in proportion to the concentration of nucleic acids in the range 1.0 x 10(-11)-1.0 x 10(-6) g/mL for yeast RNA (yRNA), 5.0 x 10(-11)-5.0 x 10(-7) g/mL for fish sperm (fsDNA) and 1.0 x 10(-10)-1.5 x 10(-6) g/mL for calf thymus DNA (ctDNA). Their detection limits were 3.0 x 10(-12), 4.0 x 10(-12) and 5.0 x 10(-11) g/mL, respectively. Therefore, the proposed method is one of the most sensitive methods available. The interaction between nucleic acids and Eu3+ -TTA-Phen is also discussed.     

Synthesis and characterization of high-sensitivity Dy,Eu co-doped CaSO4 thermoluminescent phosphor using coprecipitation technique

In this work, (99 − x)CaSO₄-Dy₂O₃–xEu₂O₃, (where x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) thermoluminescence phosphors were prepared using a coprecipitation method. The thermoluminescence (TL) dosimetry (TLD) characteristics such as TL sensitivity, dose–response, minimum detectable dose, thermal fading, and the effect of sunlight on the prepared phosphors were investigated. The obtained results indicated that the most sensitive phosphor was obtained at x = 0.05. Large thermal fading of 6% after 1 h and 26% after 24 h from irradiation followed by 71% after 1 month with no additional fading was observed within a time frame exceeding 2 months throughout the remaining duration of the investigation, which also spanned over 2 months. Despite the phosphor's high fading rate, the relative sensitivity of the prepared samples was ~90% compared with TLD-100. The marked effect of day sunlight was also determined. High dose–response within the low-dose range from 0.01 to 5 Gy was observed. The obtained results suggested that the synthesized phosphor is well suited for applications involving radiation biology and radiotherapy dosimetry.     

Modification of luminescence spectra of CaF2: Eu2+

CaF₂:Eu²⁺ is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid‐state lighting (SSL), and down‐conversion for solar cells. However, emission of CaF₂:Eu²⁺ is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue – 450 nm, green – 540 nm or red – 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF₂:Eu²⁺ to meet these requirements using co‐dopants. A Ca_0.49Sr_0.50Eu_0.01F₂ phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies. Copyright © 2015 John Wiley & Sons, Ltd.