Synthesis and luminescence properties of needle-like SrAl2O4:Eu, Dy phosphor via a hydrothermal co-precipitation method

Needle-like SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had been prepared by calcining the precursors obtained from hydrothermal process at the temperature of 1100 °C in a weak reductive atmosphere of active carbon. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction (XRD) patterns illustrated that the single-phase SrAl₂O₄ was formed at 1100 °C, which is much lower than that prepared by the traditional method. The transmission electron microscope (TEM) observation revealed the precursors and the resulted SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had well-dispersed distribution and needle-like morphology with an average diameter about 150 nm at the center and the length up to 1 μm. After irradiation by ultraviolet radiation with 350 nm for 5 min, the phosphors emit green color long-lasting phosphorescence corresponding to the typical emission of Eu²⁺ ion, both the PL spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties.     

A novel blue-emitting long-lasting proyphosphate phosphor Sr2P2O7:Eu,Y

By introducing the Y³⁺ into Sr₂P₂O₇:Eu²⁺, we successfully prepared a kind of new phosphor with blue long-lasting phosphorescence by the high-temperature solid-state reaction method. In this paper, the properties of Sr₂P₂O₇:Eu²⁺,Y³⁺ were investigated utilizing XRD, photoluminescence, luminescence decay, long-lasting phosphorescence and thermoluminescence (TL) spectra. The phosphor emitted blue light that was related to the 4f⁶5d¹-⁸S_7/2 transition of Eu²⁺. The bright blue phosphorescence could be observed by naked eyes even 8 h after the excitation source was removed. Two TL peaks at 317 and 378 K related to two types of defects appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.61 and 0.66 eV. Also, the mechanism of LLP was discussed in this report.     

Synthesis and luminescence properties of SrAl2O4:Eu,Dy nanosheets

We report an effective method to synthesize SrAl₂O₄:Eu²⁺,Dy³⁺ nanosheets. Sheet-like precursors were firstly synthesized by the solvothermal method, and acetate was used as the raw material. Then the final products were obtained by calcinating the precursor in a weak reductive atmosphere of H₂. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD) patterns, field-emission scanning electron microscopy and transmission electron microscopy (FE-SEM and TEM) , respectively. A possible growth mechanism was proposed to reveal the formation process. Luminescence properties of the SrAl₂O₄:Eu²⁺,Dy³⁺ long-lasting phosphor were analyzed by measuring the excitation spectra, the emission spectra, the afterglow decay curve and the thermoluminescence curve. Both the photoluminescence (PL) spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties compared with the phosphors prepared by using nitrates as the raw material. Furthermore, the photoluminescence intensity was even a little higher than commercial phosphors.     

PL and CL degradation and characteristics of SrAl2O4: Eu,Dy phosphors

Strontium aluminate phosphors are ideal for luminescent infrastructure materials. Their brightness and persistent glow time are much higher than previously used sulphide phosphors. Strontium aluminates prepared by the sol–gel and combustion methods are compared with commercially available strontium aluminate. High luminescent efficient SrAl₂O₄:Eu²⁺,Dy³⁺ pulsed laser deposited (PLD) thin films were also produced using the commercially available powder. Photoluminescence (PL) degradation studies showed that the phosphor intensity decreased about 20% over a period of 2 weeks under ultraviolet (UV) irradiation. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) showed that cathodoluminescence (CL) degradation is due to the formation of SrO due to electron stimulated surface reactions. The light output mechanism of the phosphor is also discussed in more detail.     

Photoluminescence of Y2O3:Eu thin film phosphors by sol-gel deposition and rapid thermal annealing

Y₂O₃:Eu³⁺ phosphor films have been developed by using the sol-gel process. Comprehensive characterization methods such as Photoluminescent (PL) spectroscopy, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the Y₂O₃:Eu³⁺ phosphor films. In this experiment, the XRD profiles show that the Y₂O₃:Eu³⁺ phosphor films crystallization temperature and optimum annealing temperature occur at about 650 and 750 °C, respectively. The optimum dopant concentration is 12 mol% Eu³⁺ and the critical transfer distance (R_c) among Eu³⁺ ions is calculated to be about 0.84 nm. Vacuum environment is more efficient than oxygen and nitrogen to eliminate the OH content and hence yields higher luminescent phosphor films. The PL emission intensity of Y₂O₃:Eu³⁺ phosphor films is also dependent on the annealing time. It was found that the H₂O impurities were effectively eliminated after annealing time of 25 s at 750 °C in vacuum environment. From the experiment results, the schematic energy band diagram of Y₂O₃:Eu³⁺ phosphor films is constructed.     

Persistent luminescence dosimetric properties of UV-irradiated SrAl2O4:Eu, Dy phosphor

Current radiation dosimetry methods involve the release of trapped charge carriers in the form of electrons-holes pairs generated by irradiation exposure of the dosimetric materials. Thermal and optical stimulations of the irradiated material freed the trapped charges that eventually recombine with interband centers producing the emission of light. The integrated intensity of the emitted light is proportional to the radiation dose exposure. In this work, we present an UV radiation dosimetry technique based on the characteristic persistence luminescence (PLUM) 4f⁶5d¹→4f⁷ electronic transition of Eu²⁺ ions in SrAl₂O₄:Eu²⁺, Dy³⁺. The dose assessment is carried out by measuring the PLUM signal integrated during a certain time. The PLUM performance of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphor exhibited a linear behavior for the first 50 s of UV irradiation. For higher UV time exposure the behavior is sublinear with no apparent saturation during a 10 min period. The PLUM dosimetry response was performed at 400 nm that corresponds to the main band component of the PLUM excitation spectrum in the 250-500 nm range. The main advantage of a dosimeter device based on the PLUM of SrAl₂O₄:Eu²⁺, Dy³⁺ is that neither thermal nor optical stimulation is required, avoiding the need of cumbersome electronic photo/thermal stimulation equipment. Due to the highly efficient 250-500 nm PLUM response of SrAl₂O₄:Eu²⁺, Dy³⁺, it could have potential application as UV radiation dosimeter in the UV range of grate human health concerns caused by UV solar radiation.     

Green-emissive transparent BaSi2O5:Eu film phosphor on quartz glass created by a sputtering thermal diffusion process

Eu²⁺-doped BaSi₂O₅ film phosphors on quartz substrates are fabricated by radio-frequency magnetron sputtering thermal diffusion. The BaSi₂O₅: Eu²⁺ phosphor crystals have some preferred orientations that are lattice-spacing matched with the crystallized β- SiO₂ crystals, and they show pore and grain boundary-free morphology with a rod-like shape fused into the crystallized β- SiO₂ crystals. The BaSi₂O₅: Eu²⁺ film phosphor has a high transparency, with a transmittance of about 30% in visible light. The BaSi₂O₅: Eu²⁺ film phosphor shows 510 nm green emission from the f–d transition of the Eu²⁺ ions, and in particular the best sample shows a green photoluminescence brightness of about 5% of a BaSi₂O₅: Eu²⁺ powder phosphor screen. These excellences in optical properties can be explained by less optical scattering at pores or grain boundaries, and less reflection at the continuously index-changed interface.     

Red emission in B- and Li-doped SrAl2O4:Eu phosphor under UV excitation

Samples of SrAl₂O₄:Eu³⁺ doped with B³⁺ and SrAl₂O₄:Eu³⁺ co-doped with B³⁺ and Li⁺ have been prepared by the solid-reaction method. The influence of B³⁺ and Li⁺ contents on luminescence property has been investigated. It is found that the substitution of B³⁺ for Al³⁺ greatly improves red emission intensity at 591, 615 and 701 nm. The dopant Li⁺ as charge compensator in SrAl₂O₄:Eu³⁺, B³⁺ can further enhance luminescence intensity. The strongest red emission is obtained in the Sr(Al_1.9, B_0.1)O₄:Eu_0.02³⁺, Li⁺_0.02 sample. The developed phosphors can be efficiently excited by ultraviolet (UV) light from 350 to 480 nm, which indicates that B³⁺ and Li⁺ co-doped SrAl₂O₄:Eu³⁺ is a good candidate phosphor applied in solid-state lighting in conjunction with white UV light-emitting diodes (LEDs).     

Photoluminescence properties of BaMgAl10O17:Eu phosphor prepared by the flux method

BaMgAl₁₀O₁₇:Eu²⁺ phosphors were synthesized by the flux method. When the appropriate amounts of fluxes are added, the synthesis temperature reduced by at least 200 °C compared with the conventional solid-state reaction method. SEM images demonstrated that addition of the flux in the process of phosphor synthesis benefitted the size and morphology of BaMgAl₁₀O₁₇:Eu²⁺ phosphor particles. Photoluminescence measurements under VUV excitation indicated that the luminescent intensity of the phosphor enhanced by adding the flux system (BaF₂+Li₂CO₃). Addition of the flux system can not only enhance the luminescence efficiency and improve the stability, but also control the morphology and grain size of the phosphor. Replacement of Ba²⁺ by Li⁺ could generate traps, which result in slightly longer decay time.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Luminescent properties of SrAl2B2O7: Ce, Tb

By using metal nitrates as starting materials, SrAl₂B₂O₇: Tb³⁺ and SrAl₂B₂O₇: Ce³⁺, Tb³⁺ powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce³⁺ to Tb³⁺ ions. The emission intensity of Tb³⁺ ions in SrAl₂B₂O₇ could be greatly intensified when Ce³⁺ ions are doped into SrAl₂B₂O₇: Tb³⁺. The decay times of SrAl₂B₂O₇: Tb³⁺ were prolonged when Ce³⁺ ions were doped. The doping of Ce³⁺ ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties.     

Synthesis and luminescent properties of Y6W2O15:Eu phosphors

In this paper, a novel phosphor, Y₆W₂O₁₅:Eu³⁺ was synthesized by thermal decomposition and phase transition of its decatungstate gel precursor. With stepwise increase of temperature to 750 °C, a crystalline phase of Y₆W₂O₁₅:Eu³⁺forms that gives intense red emission when excited at 466 nm, the emission is attributed to the Eu³⁺ ions transitions from ⁵D₀ excited states to ⁷F_J (J=0-4) ground states. The long excitation wavelength proves the Eu³⁺ transition follows the photoexcitation of the oxygen-metal (O→W lmct) charge transfer bands in yttrium tungstate. Some structural information regarding Y₆W₂O₁₅ provided by luminescence is in accord with that characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The long-wavelength excitation properties of this material may find application in the production of red phosphors for white light-emitting diodes (LEDs).     

Temperature-dependence of the structural and afterglow luminance properties of polymer/SrAlxOy:Eu,Dy composites

Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAl_xO_y:Eu²⁺,Dy³⁺ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl₂O₄ and Sr₂Al₃O₆ phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu²⁺ and Eu³⁺ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties.     

New red phosphors BaZr(BO3)2 and SrAl2B2O7 doped with Eu for PDP applications

Vacuum ultraviolet (VUV) excitation and photoluminescence (PL) characteristics of Eu³⁺ ion doped borate phosphors; BaZr(BO₃)₂:Eu³⁺ and SrAl₂B₂O₇:Eu³⁺ are studied. The excitation spectra show strong absorption in the VUV region with the absorption band edge at ca. 200 nm for BaZr(BO₃)₂:Eu³⁺ and 183 nm for SrAl₂B₂O₇:Eu³⁺, respectively, which ensures the efficient absorption of the Xe plasma emission lines. In BaZr(BO₃)₂:Eu³⁺, the charge transfer band of Eu³⁺ does not appear strongly in the excitation spectrum, which can be enhanced by co-doping Al³⁺ ion into the BaZr(BO₃)₂ lattices. The luminescence intensity of BaZr(BO₃)₂:Eu³⁺ is also increased by Al³⁺ incorporation into the lattices. The PL spectra show the strongest emission at 615 nm corresponding to the electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺ in both BaZr(BO₃)₂ and SrAl₂B₂O₇, similar to that in YAl₃(BO₃)₄, which results in a good color purity for display applications.     

Synthesis and optical properties of Er and Eu doped SrAl2O4 phosphor ceramic

We report, for the first time on luminescence from a Er³⁺ doped SrAl₂O₄ phosphor. Effects of Eu³⁺ doping were also studied. The influence of rare-earth doping in crystal structure and its optical properties were analysed by means of X-ray diffraction (XRD), Raman scattering, optical absorption, excitation and emission (PL) spectroscopy, thermally stimulated luminescence (TSL) and scanning electron microscope (SEM). Luminescence spectra and luminescence decay curves for Er³⁺ transitions in the near infrared region were recorded. The PL maximum for Eu doped SrAl₂O₄ is obtained at 620 nm and corresponds to the orange region of the spectrum. Diffraction patterns reveal a dominant phase, characteristic of the monoclinic SrAl₂O₄ compound and the presence of dopants has no effect on the basic crystal structure of SrAl₂O₄. The shapes of the glow curves are different for each dopant irradiated with either a ⁹⁰Sr-⁹⁰Y beta source, or UV light at 311 nm, and in detail the TL signals differ somewhat between Er and Eu dopants.     

Effect of Sr substitution on photoluminescent properties of BaAl2O4:Eu, Dy

Phosphor material BaAl₂O₄:Eu²⁺, Dy³⁺ with varying compositions of Sr substitution were prepared by the solid-state synthesis method. The phosphor compositions were characterized for their phase and crystallinity by XRD, SEM and TEM. Photoluminescence (PL) properties were investigated measuring PL and decay time for varying Ba/Sr compositions. The PL results show the blue shift in the luminescence properties in Sr substituted BaAl₂O₄:Eu²⁺, Dy³⁺ compared to parent BaAl₂O₄:Eu²⁺, Dy³⁺. It is probably due to the influence of 5d electron states of Eu²⁺ in the crystal field because of atomic size variation causing crystal defects. Dy³⁺ ion doping in the phosphor generates deep traps, which results in long afterglow phosphorescence.     

Radioluminescence properties of rare earths doped SrAl2O4 nanopowders

Nanopowders of SrAl₂O₄ pure and doped with rare earths were prepared via a proteic sol-gel methodology. The prepared materials presented a single crystalline phase, confirmed by XRD measurements. AFM results indicate that the average particle size is about 53 nm for SrAl₂O₄ powders. The radioluminescence spectrum of SrAl₂O₄: Eu²⁺, Dy³⁺ is composed by two intense peaks around 520 and 570 nm followed by a weaker emission peaking at 615 nm. It was observed that the intensity of RL emission during irradiation with X-rays decreased as a function of the irradiation time, indicating the build up of radiation damage in the nanopowders. The irradiated samples exhibited a persistent radiation damage that changes the colour of the sample, and also influenced the reduction in the scintillation efficiency. The saturation level of SrAl₂O₄: Eu²⁺ is 96%, exhibiting good resistance to radiation damage.     

Phosphorescent and thermoluminescent properties of SrAl2O4:Eu,Dy phosphors prepared by solid state reaction method

Long persistent SrAl₂O₄:Eu²⁺ phosphors co-doped with Dy³⁺ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl₂O₄ were observed in all the samples. The broad band emission spectra at 497 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ were observed and the emission is attributed to the 4f⁶5d¹ to 4f⁷ transition of Eu²⁺ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy³⁺ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence.     

Cathodoluminescence characteristics of particles and film of (Y, Zn)2O3:Eu phosphor prepared by spray pyrolysis

Eu-doped Y₂O₃ particles with spherical shape and fine size were prepared by spray pyrolysis. The cathodoluminescence of Y₂O₃:Eu³⁺ powder was optimized by substituting small amount of zinc atoms in place of yttrium sites. As a result, the optimized (Y, Zn)₂O₃:Eu³⁺ phosphor showed 60% improved cathodoluminescence compared with Y₂O₃:Eu³⁺ particles. The prepared (Y, Zn)₂O₃:Eu³⁺ phosphor had spherical shape and 0.726 μm in mean size. Using these particles, the thickness of the phosphor film was controlled by varying the phosphor loading. The brightness and luminous efficiency of phosphor films prepared were monitored with varying the accelerating voltage ranges from 4 to 14 kV. The dependency of the luminous efficiency on the accelerating voltage was very sensitive to the phosphor loading. As increasing the accelerating voltage from 4 to 14 kV, the brightness of phosphor films prepared was monotonically increased from 200 to 1085 cd/cm²_, but the saturation in the luminous efficiency appeared at 10 kV. The highest efficiency was achieved when the number of phosphor-particles layer was about 3. More details about the luminous efficiency and brightness were discussed with changing the phosphor loading.     

Crystallinity and morphology dependent luminescence of Li-doped Y2−xGdxO3:Eu thin film phosphors

The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y_2−xGd_xO₃:Eu³⁺ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li⁺ doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y_2−xGd_xO₃:Eu³⁺ thin films. In particular, the incorporation of Li and Gd into the Y₂O₃ lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y_1.35Gd_0.6O₃:Eu³⁺ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y₂O₃:Eu³⁺ thin films.