Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Photoluminescence and time-resolved luminescence spectroscopy of novel NaBa4(BO3)3:Tb phosphor

This paper reports the photoluminescence (PL) properties of Tb³⁺ in NaBa₄(BO₃)₃, as well as the time-resolved luminescence properties. The PL excitation spectrum exhibits intense f → f transition absorption; the PL emission spectrum shows the strongest ⁵D₄ → ⁷F₅ emission at 540 nm. The relative intensity of ⁵D₃ emission is much weaker than that of ⁵D₄ emission even in the samples with lower Tb³⁺ concentration. The ⁵D₃ → ⁵D₄ cross-relaxation produces a marked increase in the ⁵D₃ decay rate with increasing Tb³⁺ concentrations and introduces a non-exponential component into the initial part of the decay. The dipole-dipole interaction is found to be responsible for the cross-relaxation. The decay curves of ⁵D₄ → ⁷F₅ transition exhibit an initial rise phenomenon. The two exponential fitting indicates that the initial slow rise is attributed to the ⁵D₃ → ⁵D₄ cross-relaxation process.     

Citric based sol-gel synthesis and luminescence characteristics of CaLa2ZnO5:Euphosphors for blue LED excited white LEDs

A novel class of orange-red phosphors namely CaLa₂ZnO₅ (CLZ) doped with Eu³⁺ ions were prepared by adopting citrate based sol-gel method. Those were thoroughly characterized by means of XRD, SEM, Tg-DTA, photoluminescent (PL) spectral profiles. PL studies reveal that its emission intensity strongly depends on sintering temperature as well as the dopant ion (Eu³⁺) concentration. Eu³⁺ ion doped CaLa₂ZnO₅ phosphor has a strong excitation at 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The influence of the preparation method on the luminescence property was studied by comparing the emission performance of phosphors prepared by sol-gel and solid-state reaction methods along with a commercial red phosphor Y₂O₂S:Eu³⁺. Thus, the intense red emission (⁵D₀ → ⁷F₂) of the Eu³⁺ doped CLZ phosphors under blue excitation suggests them to be a potential candidate for the production of white light by blue LEDs.     

Luminescent properties of Na3Gd1−xEux(PO4)2 and energy transfer in these phosphors

A series of Eu³⁺ activated Na₃Gd_1−xEu_x(PO₄)₂ (0 ≤ x ≤ 1) phosphors were synthesized by solid-state reaction method. The structures and photo-luminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the orthorhombic Na₃Gd(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The intensities of magnetic dipole transition ⁵D₀ → ⁷F₁ and forced electric dipole transition ⁵D₀ → ⁷F₂ are comparable, and the energy ratio (⁵D₀ → ⁷F₁/⁵D₀ → ⁷F₂) is 1.1. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x = 0.62, y = 0.38), which is due to the ⁵D₀ → ⁷F_J transitions of Eu³⁺ ions. The correlation between the structure and the photo-luminescent properties of the phosphors was studied. The energy transfer and concentration quenching of the phosphors were discussed. Na₃Gd_1−xEu_x(PO₄)₂ has a potential application for white light-emitting diodes.     

Preparation and its luminescent properties of AlPO4:Eu phosphor for w-LED applications

Orange-reddish-emitting phosphor AlPO₄:Eu³⁺ were fabricated by solid-state reactions at high temperature. X-ray diffraction analysis revealed that AlPO₄ doped with 3 mol% of Eu³⁺ (AlPO₄:0.03Eu³⁺) was pure orthorhombic phase. The photoluminescence study shows that the intensity of magnetic dipole transition (⁵D₀ → ⁷F₁) at 594 nm dominates over that of electric dipole transition (⁵D₀ → ⁷F₂) at 613 nm. The optimum concentration of Eu³⁺ for the highest luminescence is found to be 3 mol%. The PL excitation spectrum is composed of CTB of Eu-O and excitation lines of Eu³⁺ ions. The strongest excitation lines appeared at 392 nm. The color coordinates, quantum yield and lifetime for AlPO₄:0.03Eu³⁺ were measured. All the spectrum features indicate that AlPO₄:Eu³⁺ might be a promising phosphor for display devices or w-LEDs.     

Synthesis and photoluminescence properties of color-tunable BaLa2WO7:Eu phosphor

Color-tunable phosphors BaLa_2−xEu_xWO₇ were synthesized via a solid-state reaction. The absorption, excitation, emission and decay curves were obtained to study the luminescence properties. The experimental results indicate that BaLa_2−xEu_xWO₇ phosphors have two regions in the excitation spectra: one is assigned to the charge-transfer state (CTS) band at about 338 nm, and the other is assigned to the intra-4f transitions at 360-600 nm. The emission spectra of BaLa_2−xEu_xWO₇ phosphors excited at 395 nm exhibit a series of sharp peaks, which are attributed to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. Luminescence from higher excited states, such as ⁵D₁, ⁵D₂, and ⁵D₃, were also observed at low Eu³⁺ concentration. The optimal emission intensity of ⁵D₀ → ⁷F₂ red emission is at x = 0.4 (BaLa_1.6Eu_0.4WO₇). The chromaticity coordinates of BaLa_2−xEu_xWO₇ phosphors vary with Eu³⁺ content from white, orange-red, to red, making it a candidate for a white-light-emitting phosphor in UV-LEDs.     

A novel red-emitting phosphors K2Ba (MoO4)2: Eu, Sm and improvement of luminescent properties for light emitting diodes

The novel red-emitting phosphors K₂Ba(MoO₄)₂: Eu³⁺, Sm³⁺ were prepared by solid-state reaction and their crystal structures, photo luminescent characteristics were investigated. The results show that all samples can be excited efficiently by UV (397 nm) and blue (466 nm) light, which are coupled well with the characteristic emission from UVLED and blue LED, respectively. A small amount of Sm³⁺, acting as a sensitizer, increased the energy absorption around 400 nm. In the Eu³⁺-Sm³⁺ co-doped system, both Eu³⁺ and Sm³⁺ f-f transition absorptions are observed in the excitation spectra, the intensities of the main emission line (⁵D₀ → ⁷F₂ transition of Eu³⁺ at 616 nm) are strengthened because of the energy transition from Sm³⁺ to Eu³⁺. The doping concentration of Eu³⁺-Sm³⁺ was optimized. The approach to charge compensation was used: Ba²⁺ → Eu³⁺/Sm³⁺ + X⁻ (X = F, Cl, and Br), and the influence of charge compensation on the luminescent intensity of phosphors is investigated.     

Synthesis and luminescence properties of clew-like CaMoO4:Sm, Eu

Eu³⁺ and Sm³⁺ co-doped CaMoO₄ microclews have been successfully synthesized via a facile hydrothermal method directly in surfactant-free environment. The as-prepared phosphor present clew-like agglomerates composed of 40 nm nanosheets under the moderated reaction temperature. The red phosphor CaMoO₄:Eu³⁺, Sm³⁺ can generate a strong absorption line at 405 nm, originating from ⁶H_5/2 → ⁶P_5/2 transition of Sm³⁺, which is suitable for the emission of the near-ultraviolet light-emitting diodes (∼400 nm). Energy transfer between Sm³⁺ and Eu³⁺ is detected from the varied photoluminescence spectra with different Eu³⁺ concentrations and the energy transfer mechanism is clarified via the photoluminescence spectra. When Sm³⁺ is excited (405 nm), the electron is excited from ⁶H_5/2 to ⁶P_5/2, and then relaxed to ⁴G_5/2. It jumps from ⁴G_5/2 to the lower levels corresponding to the emissions of Sm³⁺; meanwhile, the transfers from ⁴G_5/2 state of Sm³⁺ ion to ⁵D₀ state of Eu³⁺ ion come out. The transition of ⁵D₁ → ⁷F_J (J = 0, 1, 2) does not appear indicating that the transfer from ⁴G_5/2 state of Sm³⁺ to ⁵D₀ state rather than ⁵D₁ state of Eu³⁺ is the energy transfer pathway.     

Preparation and luminescence characterization of new carbonate (Y2(CO3)3·nH2O:Eu) phosphors via the hydrothermal route

A new Eu³⁺-activated Y₂(CO₃)₃·nH₂O phosphor was successfully prepared via the hydrothermal process using urea as a reaction agent. Y₂(CO₃)₃·nH₂O:Eu³⁺ phosphors displayed an intense red emission at 615 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions under 254 nm excitation. The intensity of this emission was significantly increased with a rise in the hydrothermal temperatures. The study of photoluminescence properties demonstrated that Y³⁺ ions were replaced by Eu³⁺ ions in the host lattice at the 9-coordination sites. With an increase in heating temperatures, the morphology of Y₂(CO₃)₃·nH₂O:Eu³⁺ powders changed from a spherical to a rod-like shape. Calcination at elevated temperatures resulted in thermal decomposition of Y₂(CO₃)₃·nH₂O:Eu³⁺ to form Y₂O₃:Eu³⁺. The formed Y₂O₃:Eu³⁺ powder exhibited a rod-like morphology with an intense red emission.     

Eu/Sm ions co-doped white light luminescence SrSiO3 glass-ceramics phosphor for White LED

Eu²⁺/Sm³⁺ co-doped silicate glass was prepared by high temperature melting under reducing atmosphere and the Eu²⁺/Sm³⁺ co-doped SrSiO₃ transparent glass-ceramics were obtained after heat-treatment. X-ray diffraction (XRD) and Raman spectra confirmed the formation of SrSiO₃ nano-crystals in the glass matrix. The photoluminescence excitation (PLE) spectra and photoluminescence (PL) spectra of the samples were measured. A broad emission band from 400 nm to 550 nm due to the 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ was observed, as well as several sharp emission peaks at 563 nm, 600 nm, 646 nm and 713 nm ascribed to the 4f → 4f transitions of Sm³⁺. The luminescence properties of the glass ceramics with different molar ratio of Eu²⁺/Sm³⁺ were studied and the corresponding chromaticity coordinates were calculated. The ultraviolet light-emitting diode (UV-LED) excitable glass-ceramics emitting white light were obtained by tuning the relative emission intensity of Eu²⁺ and Sm³⁺. The results indicate that the Eu²⁺/Sm³⁺ co-doped SrSiO₃ transparent glass-ceramics can be used as a potential matrix material for White LED under UV-LED excitation.     

Preparation and structural properties of Lu2O3:Eu submicrometer spherical phosphors

Monodisperse non-agglomerated Lu₂O₃:Eu³⁺ submicrometer spheres were obtained by the homogeneous precipitation technique with subsequent annealing for spheres crystallization. The morphological and structural parameters of the Lu₂O₃:Eu³⁺ crystalline spheres prepared were investigated by the electron microscopy methods, thermal analysis (TG-DTA), X-ray diffractometry (XRD), X-ray photoelectron (XPS) and FT-IR spectroscopy. The influence of the annealing temperature on the morphology and sphericity was shown. Eu³⁺-doped lutetium oxide spheres were characterized by effective luminescence under X-ray excitation in the λ = 575-725 nm range corresponding to ⁵D₀ → ⁷F_J transitions (J = 0-4) of Eu³⁺ ions. It was shown that the X-ray luminescence efficiency of the Lu₂O₃:Eu³⁺ spherical phosphors prepared strongly depend on annealing temperature and dopant concentration.     

Multiwavelength excited novel red-emitting phosphor Eu-activated Li2Zn2(MoO4)3

Eu³⁺-activated Li₂Zn₂(MoO₄)₃ multiwavelength excited red-emitting phosphors were synthesized via a solid state reaction. The structure and photoluminescence characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometry, respectively. The excitation spectrum included a strong broadband ranging from 250 to 350 nm and some sharp peaks at 363, 384, 395, 465, and 533 nm, which matchs the radiations of near-UV or blue light-emitting diodes chip well. Upon excitation either of near-UV or blue even green light, the intense red emission with 615 nm peak can be observed, which is ascribed to the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The chromaticity coordinates (x = 0.65, y = 0.34) of the as-obtained phosphor is very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that Eu³⁺-doped Li₂Zn₂(MoO₄)₃ wavelength-conversion material to be suitable candidate red component for phosphor-converted white light-emitting diodes.     

Synthesis and photoluminescence of Eu by co-doping Eu and Cl in Sr2P2O7 under air atmosphere

A novel phosphor Sr₂P₂O₇ co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu³⁺ substitute Sr²⁺ site and subsequently to reduce Eu³⁺ to Eu²⁺, XPS results confirmed that some amount of Eu³⁺ ions could be reduced to Eu²⁺ ions under air atmosphere at high temperature. The reduction tendency of Eu³⁺ depends not only on the doping Cl⁻ content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu²⁺, 592 nm and 613 nm assigned to the characteristic transitions of ⁵D₀-⁷F_1,2 of Eu³⁺. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu³⁺ on the Sr²⁺ sites in the investigated phosphors.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Photoluminescent properties of LiSrxBa1−xPO4:RE (RE = Sm, Eu) f-f transition phosphors

Rare-earth ions (Sm³⁺ or Eu³⁺) doped LiSr_xBa_1−xPO₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) f-f transition phosphor powders were prepared by a high temperature solid-state reaction. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the phase structure of the sample changes from LiBaPO₄ to LiSrPO₄ when x changes from 0 to 1.0. The excitation spectra indicate that only direct excitation of rare earth ions (Sm³⁺ or Eu³⁺) can be observed. The doped rare earth ions show their characteristic emission in LiSr_xBa_1−xPO₄, i.e., Eu³⁺⁵D₀-⁷F_J (J = 0, 1, 2, 3, 4), Sm³⁺⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2), respectively. The dependence of the emission intensities of the LiSr_xBa_1−xPO₄:Sm³⁺ and LiSr_xBa_1−xPO₄:Eu³⁺ phosphors on the x value and Ln³⁺ (Ln³⁺ = Sm³⁺, Eu³⁺) concentration is also investigated.     

Luminescence properties of Eu and Eu doped calcium-deficient hydroxyapatite prepared in air

Eu-doped calcium-deficient hydroxyapatite Ca_8.95Eu_0.05HPO₄(PO₄)₅OH (designated CDHA:Eu) was prepared via the coprecipitation method and calcined in air. Phase purity, crystal structure and morphology of the CDHA:Eu were characterized using X-ray diffraction spectrometer and scanning electron microscopy. The photoluminescence excitation and emission spectra of Eu²⁺ and Eu³⁺ ions were measured using luminescence spectrometer. The emission spectra showed a broad emission band centered at 450 nm corresponded to the typical 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions, and sharp peaks corresponded to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ ions. This research was focused on the site-distribution of Eu³⁺ ions. The Eu³⁺ in different sites had different spectroscopic features and the charge compensation mechanisms were also discussed.     

Vacuum ultraviolet spectroscopic properties of KSrPO4:Tb

KSrPO₄:Tb³⁺ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544 nm, the band in the region of 120-162 nm can be attributed to be the overlap of host absorption and charge transfer transition of O²⁻ → Tb³⁺, and the band ranging from 162 to 300 nm was assigned to the f-d transition of Tb³⁺. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ under the excitation of 147 nm. Optimal emission intensity was obtained when x = 7% in KSr_1-xPO₄:xTb³⁺ and the luminescent chromaticity coordinates were calculated to be (x = 0.317, y = 0.522) for KSr_0.93PO₄:7%Tb³⁺.     

Upconversion luminescence in Er/Yb codoped Y2CaGe4O12

Calcium yttrium tetrametagermanates Y₂CaGe₄O₁₂ doped with Er³⁺ and Er³⁺/Yb³⁺ reveal upconversion emission in visible spectral range under near-infrared excitation, λ_ex = 980 nm. For the solid solution Er_xY_2−xCaGe₄O₁₂ concentration dependencies for the green and red lines of the visible emission around 526 nm (²H_11/2 → ⁴I_15/2), 545 nm (⁴S_3/2 → ⁴I_15/2) and 670 nm (⁴F_9/2 → ⁴I_15/2) show the optimal value for the sample x = 0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y₂CaGe₄O₁₂:Er³⁺ is discussed for an 808 nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y₂CaGe₄O₁₂:Er³⁺ and Y₂CaGe₄O₁₂:Er³⁺, Yb³⁺ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ_ex = 1064 nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition ⁴I_13/2 → ⁴I_15/2 in erbium ions has been detected.     

Luminescence studies of Ba1−xMg2−y(PO4)2:xEu, yMn phosphor

The phosphors BaMg₂(PO₄)₂ doped with Eu²⁺ and Mn²⁺ solely or doubly were prepared by solid state reaction, and their luminescent properties were also investigated. Under the excitation of 322 nm, it has been observed a broad blue emission band centered at 417 nm and a red emission band centered at about 665 nm, resulting from Eu²⁺ and Mn²⁺, respectively. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the emission spectra of Eu²⁺ and the excitation spectra of Mn²⁺. According to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission, efficiencies of energy transfer were calculated. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

Luminescent and magnetic properties of YVO4:Ln@Fe3O4 (Ln = Eu or Dy) nanocomposites

A series of core-shell bifunctional magnetic-optical YVO₄:Ln³⁺@Fe₃O₄ (Ln³⁺ = Eu³⁺ or Dy³⁺) nanocomposites have been successfully synthesized via two-step method. The nanocomposites have the advantage of high magnetic responsive and unique luminescence properties. The structure, luminescent and magnetic properties of the nanocomposites were investigated by XRD, TEM, PL and VSM. The maximum emission peaks of the nanocomposites are at 618 nm (doping Eu³⁺), 574 nm (doping Dy³⁺). The special saturation magnetization of the nanocomposites is 54 emu/g. The diameter of the nanocomposites is 400-900 nm.