Synthesis of novel Dy activated phosphate phosphors for NUV excited LED

The new trivalent dysprosium activated X₆AlP₅O₂₀ (where X=Sr, Ba, Ca and Mg) phosphors were prepared by the combustion method. The prepared phosphors are characterized by XRD, photoluminescence and SEM techniques. Excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The effect of the Dy³⁺ concentration on the luminescence properties of X₆AlP₅O₂₀:Dy³⁺ (where X=Sr, Ba, Ca and Mg) phosphors is studied. Ca₆AlP₅O₂₀ phosphors show strong PL emission intensity around 25 times more as compared to Ba₆AlP₅O₂₀, Sr₆AlP₅O₂₀ and Mg₆AlP₅O₂₀ phosphors. The investigated prepared phosphors are suitable for a NUV excited LED.     

Emission analysis of Eu:MgLaLiSi2O7 powder phosphor

Newly synthesized reference MgLaLiSi₂O₇ and red luminescent Eu³⁺:MgLaLiSi₂O₇ powder phosphors have been successfully developed by a solid-state reaction method to analyze their emission and structural properties from the measurement of their XRD, SEM, FTIR and PL spectra. Emission spectra of Eu³⁺ powder phosphors have shown strong red emissions at 613 nm (⁵D₀→⁷F₂). These phosphors have also shown bright red emissions under a UV source. Based on the red emission performance, the Eu³⁺ concentration has been optimized to be at 0.3 mol%.     

Optical and fluorescence spectroscopy of Eu2O3-doped P2O5-K2O-KF-MO-Al2O3 (M = Mg, Sr and Ba) glasses

Fluorophosphate glasses of composition, P₂O₅ + K₂O + KF + MO + Al₂O₃ + xEu₂O₃ (M = Mg, Sr and Ba; x = 0.01, 0.05, 0.1, 1.0, 2.0, 4.0 and 6.0 mol%) were prepared and characterized their optical properties. Crystal-field (CF) analysis revealed a relatively weak CF strength around Eu³⁺ ions in the Ba based fluorophosphate glasses. The Judd-Ofelt parameters have been estimated from the oscillator strengths of ⁷F₀ → ⁵D₂, ⁷F₀ → ⁵D₄ and ⁷F₀ → ⁵L₆ absorption transitions of Eu³⁺ ions and were used to evaluate the radiative properties of the ⁵D₀ → ⁷F_J (J = 0-4) transitions. Considerable variation has been observed in the relative intensity ratio of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions due to change in the alkaline earth metal ions. The decay of the ⁵D₀ level shows single exponential and less sensitive to Eu³⁺ ions concentration as well as MgO/SrO/BaO modifiers.     

Eu photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2-B2O3-PbO2 glasses system

In this work, Eu³⁺-doped lead borosilicate glasses (SiO₂-B₂O₃-PbO₂) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500 °C show a precipitated crystalline phase with sizes 11 and 21 nm, respectively. Besides, as the temperature increases from 350 to 300 K a strong Eu³⁺ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu³⁺ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu³⁺ transitions ⁵D₀→⁷F₂, at 612 nm, ⁵D₀→⁷F₁, at 595 nm, and ⁵D₀→⁷F₀, at 585 nm. It was also observed that the ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ PL bands at 655 and 700 nm, respectively, show a continuous decrease in intensity as the temperature increases.     

Synthesis and luminescence properties of red-emitting phosphors NaY0.87Eu0.13(WO4)1.2(MoO4)0.8

A series of NaY_1−yEu_y(WO₄)_2−x(MoO₄)_x (x=0−2 and y=0.06−0.15) phosphors have been prepared by a combustion route. X-ray powder diffraction, photoluminescence excitation and emission spectra were used to characterize the resulting samples. The excitation spectra of these phosphors show the strongest absorption at about 396 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. Their emission spectra show an intense red emission at 616 nm due to the ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺. As the Mo content increases, the intensity of the ⁵D₀→⁷F₂ emission of Eu³⁺ activated at wavelength of 396 nm increases and reaches a maximum when the relative ratio of Mo/W is 2:3. The intense red-emission of the tungstomolybdate phosphors at near-UV excitation suggests that the material is a potential candidate for white light emitting diode (WLEDs).     

Synthesis and luminescence investigation of RE (Eu, Tb and Ce)-doped lithium silicate (Li2SiO3)

Synthesis and photoluminescence (PL) investigations of lithium metasilicate doped with Eu³⁺, Tb³⁺ and Ce³⁺ were carried out. PL spectra of Eu-doped sample showed peaks corresponding to the ⁵D₀→⁷F_j (j=1, 2, 3 and 4) transitions under ultraviolet excitation. Strong red emission coming from the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ ion suggested the presence of the dopant ion in structurally disordered environment. Tb³⁺-doped silicate sample showed blue-green emission corresponding to the ⁵D₄→⁷F_j (j=6, 5 and 4) transitions. Ce-doped sample under excitation from UV, showed a broad emission band in the region 350-370 nm with shoulders around 410 nm. The fluorescence lifetimes of Eu³⁺ and Tb³⁺ ions were found out to be 790 and 600 μs, respectively. For Ce³⁺, the lifetime was of the order of 45 ns. PL spectra of the europium- and terbium-doped samples were compared with commercial red (Y₂O₃:Eu³⁺) and green (LaPO₄:Tb³⁺) phosphors, respectively. It was found that the emission from the doped silicate sample was 37% of the commercial phosphor in case of the Tb-doped sample and 8% of the commercial phosphor in case of the Eu-doped sample.     

The luminescence and structural characteristics of Eu- doped NaSrB5O9 phosphor

A red-emitting phosphor NaSrB₅O₉:Eu³⁺ was synthesized by employing a solid-state reaction (SSR) method. The structures of the phosphors were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman studies. The band at ~282 nm in the excitation spectra indicated the charge transfer band (CTB) of B-O in the host, whereas the CTB of Eu-O was observed at ~275 nm for the NaSrB₅O₉:Eu³⁺ (Eu³⁺=1 at.%) phosphor, which was supported by diffuse reflectance spectroscopy (DRS) measurements. The photoluminescence (PL) measurements exhibited a strong red emission band centered at about 616 nm (⁵D₀→⁷F₂) under an excitation wavelength of 394 nm (⁷F₀→⁵L₆). Upon host excitation at 282 nm, the pristine NaSrB₅O₉ exhibited a broad UV emission centered at ~362 nm. The energy transfer from host to Eu³⁺ ions was confirmed from luminescence spectra, excited with a 355 nm Nd:YAG laser. In addition, the asymmetric ratios indicate a higher local symmetry around the Eu³⁺ ion in the host. The calculated CIE (Commission International de l′Eclairage) coordinates displayed excellent color purity efficiencies (around 99.7%) compared to other luminescent materials.     

Luminescence in trivalent rare earth activated Sr4Al2O7 phosphor

In this paper we report the combustion synthesis of trivalent rare-earth (RE³⁺ = Dy, Eu and Ce) activated Sr₄Al₂O₇ phosphor. The prepared phosphors were characterized by the X-ray powder diffraction (XRD) and photoluminescence (PL) techniques. Photoluminescence emission peaks of Sr₄Al₂O₇:Dy³⁺ phosphor at 474 nm and 578 nm in the blue and yellow region of the spectrum. The prepared Eu³⁺ doped phosphors were excited by 395 nm then we found that the characteristics emission of europium ions at 615 nm (⁵D₀?⁷F₂) and 592 nm (⁵D₀?⁷F₁). Photoluminescence (PL) peaks situated at wavelengths of 363 and 378 nm in the UV region under excitation at around 326 nm in the Sr₄Al₂O₇:Ce³⁺ phosphor.     

Highly luminescent red light phosphor CaTiO3:Eu under near-ultraviolet excitation

The Eu-doped CaTiO₃ particles with a good crystallinity were prepared via sol-gel method. The phosphors showed a strong red emission corresponding to ⁵D₀→⁷F₂ (618 nm) of Eu³⁺ under the near-ultraviolet excitation (400 nm). X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), photoluminescent (PL) analysis and Brunauer-Emmett-Teller (BET) specific surface area measurement were utilized to characterize the CaTiO₃:Eu³⁺ particles. The concentration quenching and thermal quenching of the samples were discussed as well. The optimal concentration and the calcination temperature were 16 mol% of Eu³⁺ and 1400 °C for these phosphors, and the possible reason was discussed as well. CaTiO₃:Eu³⁺ is a promising red phosphor under near-ultraviolet excitation for various applications.     

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).     

Synthesis and photoluminescent properties of YVO4:Eu nano-crystal phosphor prepared by Pechini process

A sol-gel technique emphasizing the Pechini process has been employed for the preparation of nano-crystal Eu³⁺-doped YVO₄ phosphor. The precursor powders were heated at 800 °C for 3 h to obtain good crystallinity with better luminescence. XRD results indicate that the second phase is not presented when the Eu³⁺ ion concentration is increased up to 50 mol%. The absorption and photoluminescent (PL) studies indicated that the energy is absorbed first by the host and then transferred to the emitting level of the Eu³⁺ ions. Excitation at 318 nm in terms of Eu³⁺ concentrations in YVO₄ powders shows that the YVO₄ phosphors display bright red luminescence at about 618 nm belonging to the ⁵D₀→⁷F₂ electric dipole transition, and a weak band in the orange region of the ⁵D₀→⁷F₁ transition at 594 nm. In addition, the time-resolved ⁵D₀→⁷F₂ transition presents a single-exponential decay behavior, revealing the decay mechanism of the ⁵D₀→⁷F₂ transition is a single decay component between Eu³⁺ ions only. The saturation of the emission intensity excited by the CTS when the Eu³⁺ concentration is 10 mol%. The concentration quenching is active when the Eu³⁺ concentration is larger than 10 mol%, and the critical distance is about 5.75 Å.     

Self-assembled CaMoO4 and CaMoO4:Eu hierarchical superstructures: Facile sonochemical route synthesis and tunable luminescent properties

Tetragonal CaMoO₄ and CaMoO₄:Eu³⁺ with various novel three-dimensional (3D) hierarchical architectures were successfully synthesized via a facile, efficient sonochemistry process in the absence of any surfactant or template. XRD, EDS, FE-SEM, and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that morphology modulation could be easily realized by changing pH value of the precursor. The pH value of the precursor not only affected the substructures of the hierarchical structures, but also determined the size distributions of the final products. The formation mechanism for different hierarchical architectures was proposed on the basis of time-dependent experiments. The luminescence spectra showed that CaMoO₄:Eu³⁺ phosphors can be effectively excited by the near ultraviolet (UV) (396 nm) and blue (466 nm) light, and exhibited strong red emission around 615 nm, which was attributed to the Eu³⁺⁵D₀→⁷F₂ transition. Compared with Y₂O₃:Eu³⁺ phosphor, CaMoO₄:Eu³⁺ is much more stable, efficient and suitable, therefore, this phosphors could be a promising red component for possible applications in the field of LEDs.     

New promising phosphors Ba3InB9O18 activated by Eu/Tb

Borate Ba₃InB₉O₁₈ (BIBO) has been adopted as a host material for phosphors for the first time. Lanthanide ions (Eu³⁺/Tb³⁺)-doped BIBO phosphors have been synthesized by solid-state reaction and luminescent properties investigated under ultravoilet (UV) excitation. For red phosphor BIBO:Eu, dominant emission peaking at 590 nm was attributed to ⁵D₀→⁷F₁ transition of Eu³⁺, which confirmed that the local site of Eu³⁺ occupied by In³⁺ ion in BIBO crystal lattice is at inversion symmetry center. Optimum Eu³⁺ concentration of BIBO:Eu under UV excitation with 227 nm wavelength is around 40%. The green phosphor BIBO:Tb showed bright green emission at 550 with 232 nm light excited and optimal of Tb³⁺ concentration measured in BIBO is about 8%. The corresponding luminescence mechanisms of Ln-doped BIBO (Ln=Eu³⁺/Tb³⁺) were analyzed. The luminescent intensity of Tb³⁺ can be significantly improved by co-doping of Bi³⁺ in the BIBO:Tb lattice. The likely reason was proposed in terms of the different interactions of the host lattice with these ions, and of these ions with each other.     

Photoluminescence properties of Sr(Y, Gd)2O4:Euunder VUV excitation

Vacuum ultraviolet (VUV) excitation and photoluminescence (PL) properties of Sr(Y, Gd)₂O₄ doped with Eu³⁺ were studied. The excitation spectra of SrY_1.9Eu_0.1O₄ and SrY_1.0Gd_0.9Eu_0.1O₄ had absorption in the VUV region with the absorption band edge at 149 nm, while the absorption of SrGd_1.9Eu_0.1O₄ in the VUV region was weak, which could be due to the narrow host band gap and no efficient energy transfer occurred in the VUV region. The PL spectra of all samples exhibited the characteristic emission of Eu³⁺ with the red ⁵D₀-⁷F₂ transition (611 nm) being the most prominent group.     

Sol-gel synthesis, structural and optical properties of rare earth ions (Sm or Dy) activated Ca3Ga2Si3O12 powder phosphors

Structural, morphological and optical properties of rare earth ions (RE³⁺=Sm³⁺ or Dy³⁺) activated Ca₃Ga₂Si₃O₁₂ (CaGaSi) phosphors synthesized by the sol-gel method are reported. XRD results confirmed the cubic phase structure of RE³⁺:CaGaSi phosphors. From the SEM images of RE³⁺:CaGaSi phosphors, it is observed that the particles are agglomerated. Photoluminescence spectra of Sm³⁺:CaGaSi phosphors have shown bright orange red emission at 598 nm (⁴G_5/2→⁶H_7/2) with an excitation wavelength of λ_exci=401 nm. In the case of Dy³⁺:CaGaSi phosphors bright yellow emission has been observed at 574 nm (⁴F_9/2→ ⁶H_13/2) with λ_exci=451 nm. From the PL spectral results, the rare earth ion concentration of CaGaSi phosphors is optimized.     

Enhancement of luminescence intensity and increase of emission lifetime in Eu-doped 3CdO-Al2O3-3SiO2 amorphous system

Intense photoluminescence at room temperature was observed in amorphous cadmium aluminum silicate doped with europium prepared by the sol-gel method. The structure of the 3CdO-Al₂O₃-3SiO₂:Eu³⁺ system (CAS:Eu³⁺) has been determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The excitation and the emission spectra indicated that the red characteristic emission (611 nm) of CAS:Eu³⁺ under UV excitation due to ⁵D₀→⁷F₂ electric dipole transition is the strongest. Both XRD data and the emission ratio of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) reveal that the Eu³⁺ is in a site without inversion symmetry. The maximum photoluminescence intensity has been obtained for 25 mol% concentration of Eu³⁺ in CAS, and the intensity enhancement and lifetime increase of Eu³⁺ with increasing sintering temperature were observed due to the less OH-content in the samples.     

Sol-gel synthesis and photoluminescence of CaSiO3:Eu nanophosphors using novel silicate sources

In this paper, seven kinds of silane coupling reagents were employed as silicate sources to prepare CaSiO₃:Eu³⁺ phosphors by the sol-gel method. The different silicate precursors were used to adjust the microstructure and size of the resulting phosphors. The crystallite size of phosphors is in the range of 30-35 nm and some of them show regular microstructure after high-temperature thermolysis. The photoluminescence properties show that all of them exhibit the characteristic fluorescence ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of the Eu³⁺ ion and the strongest one is the red emission at 610 nm. Furthermore, the emission quantum efficiency (η) of the ⁵D₀ Eu³⁺ excited state has been calculated to be around 33% from the emission spectrum and the lifetime of the Eu³⁺ first excited level (τ, ⁵D₀).     

Preparation and luminescent properties of phosphor MGd2(MoO4)4: Eu (M=Ca, Sr and Ba)

Intense red emitting phosphors MGd₂(MoO₄)₄: Eu³⁺ (M=Ca, Sr and Ba) have been synthesized by the simple sol-gel technique. The formation processes and the phase impurity of phosphors are characterized by thermogravimetry-differential thermal analysis (TG-DTA) and power X-ray diffraction (XRD). The narrower size distribution and the regular shape of the phosphor particles are also measured by Field emission scanning electronic microscopy (FE-SEM). Photo-luminescent properties of the phosphors are performed at room temperature. Their excitation spectra present strong absorption at 395 nm near-UV light and 465 nm blue light, which match well with commercial LED chips. The phosphors exhibit satisfactory and excellent red light dominated by 616 nm and their photoluminescence intensity is about 3-4 times stronger than that of phosphor YAG under the 465 nm excitation. In addition, the optimal concentrations of Eu³⁺ for phosphors MGd₂(MoO₄)₄ (M=Ca, Sr and Ba) have also been determined.     

Sol-gel growth of Gd2MoO6:Eu nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6:Eu) and their luminescent properties

SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors. The XRD results demonstrate that the Gd₂MoO₆:Eu³⁺ layers on the SiO₂ spheres begin to crystallize after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd₂MoO₆:Eu³⁺ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu³⁺ shows a strong PL luminescence (dominated by ⁵D₀-⁷F₂ red emission at 613 nm) under the excitation of 307 nm UV light. The PL intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles.     

Luminescent properties of R2(MoO4)3:Eu (R=La, Y, Gd) phosphors prepared by sol-gel process

A series of red phosphors R_0.8Eu_1.2(MoO₄)₃ (R=La, Y, and Gd) have been synthesized by sol-gel method. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA), and the properties of these resulting phosphors have also been characterized by photoluminescence (PL) spectra and reflectance spectra. Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and the size of the samples. The results of TG-DTA and XRD indicated that all of the R_0.8Eu_1.2(MoO₄)₃ (R=La, Y, and Gd) phosphors crystallized completely at 650 °C. Y_0.8Eu_1.2(MoO₄)₃ and Gd_0.8Eu_1.2(MoO₄)₃ have two structures, monoclinic and orthorhombic, while La_0.8Eu_1.2(MoO₄)₃ only adopts monoclinic structure. The luminescent properties of phosphors R_0.8Eu_1.2(MoO₄)₃ (R=La, Y, and Gd) are dependent on their structures to some extent. The orthorhombic Y_0.8Eu_1.2(MoO₄)₃ and Gd_0.8Eu_1.2(MoO₄)₃ phosphors show very similar luminescent properties, which differ from those of phosphors with monoclinic structure. For all of R_0.8Eu_1.2(MoO₄)₃ (R=La, Y, and Gd) phosphors, intense red emission is obtained by exciting at ∼394 and ∼465 nm which are owing to the sharp ⁷F₀→⁵L₆ and ⁷F₀→⁵D₂ lines of Eu³⁺. Two strongest lines at 394 and 465 nm in excitation spectra of these phosphors match well with the two popular emissions from near-UV and blue GaN-based LEDs, so they could be used as red components for white light-emitting diodes.