Luminescent properties of nanoparticles LaSrAl<Subscript>3</Subscript>O<Subscript>7</Subscript>:RE<Superscript>3+</Superscript> (RE = Eu,Tb) via the citrate sol–gel method

Phosphors of nanoparticles LaSrAl₃O₇:RE³⁺ (RE = Eu, Tb) have been prepared by a sol–gel method. The structure and luminescent properties of LaSrAl₃O₇:Eu³⁺ and LaSrAl₃O₇:Tb³⁺ phosphors were characterized by X-Ray diffraction (XRD) and atomic force microscopy (AFM), photoluminescence excitation and emission spectra were utilized. From XRD patterns, it is indicated that the phosphor LaSrAl₃O₇ forms without impurity phase at 900 °C. From AFM images, it is shown that the crystal size of the phosphors are about 60–80 nm. Upon excitation with ultraviolet (UV) irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀–⁷F₂ transition of Eu³⁺, and at around 543 nm corresponding to the ⁵D₄–⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺ (or Tb³⁺) concentration and annealing temperature were also studied in detail.     

Tunable luminescence and energy transfer properties in Ca<Subscript>2−x</Subscript>NaMg<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>12</Subscript>:xEu<Superscript>3+</Superscript> phosphors

Novel broadband luminescence phosphors Ca_2?xNaMg₂V₃O₁₂:xEu³⁺ have been successfully prepared via the conventional high-temperature solid-state reaction. The effects of concentrations of doped Eu³⁺ and introducing Li⁺, K⁺ on the luminescent properties of phosphor were studied. X-ray diffraction, GSAS structural refinement and photoluminescence spectra were used to characterize the samples. The refinement data ensured where the doped Eu³⁺ ions occupied the lattice site in the host. Under 355 nm excitation, the emission peak of Ca₂NaMg₂V₃O₁₂:Eu³⁺ phosphors are located at 610 nm (red) ascribed to the electric dipole transition of Eu³⁺ from ⁵D₀ → ⁷F₂. In the range of 400–575 nm, Ca₂NaMg₂V₃O₁₂:Eu³⁺ phosphors have broad emission bands attributed to charge transfer of \({\text{VO}}_4^{3 - }\) group. Energy transfer mechanism, energy transfer efficiency and critical distance (R_c) of \({\text{VO}}_4^{3 - }\) → Eu³⁺ would be analyzed. The emitting color of Ca₂NaMg₂V₃O₁₂:Eu³⁺ could be tunable from blue-green to near white light.     

Sol–gel preparation and luminescence of RE<Subscript>3</Subscript>BO<Subscript>6</Subscript>: Dy<Superscript>3+</Superscript> (RE = La,Y, Gd) microparticles with hybrid precursors

Dysprosium ion activated RE₃BO₆ (RE = La, Y, Gd) polycrystalline phosphors have been prepared via a modified sol–gel process with urea as fuel and rare earth nitrates as precursors. The crystal phase and the morphology of the phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average particle size after heat treatment at 1,000 °C is around 5 μm by particle size determination technique. The characteristic transitions of Dy³⁺ due to ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2. → ⁶H_13/2 (yellow) can be observed in the emission spectra and the yellow-to-blue intensity ratio (Y/B) can be changed with the variety of the doped concentration of Dy³⁺ ion. Zeta potential shows the relationship between the surface charges to the pH value in suspension.     

Hydrothermal synthesis and multi-color photoluminescence of GdVO<Subscript>4</Subscript>: Ln<Superscript>3+</Superscript> (Ln = Sm,Dy, Er) sub-micrometer phosphors

GdVO₄: 5 mol% Ln³⁺ (Ln = Sm, Dy, Er) sub-micrometer phosphors have been synthesized by a facile hydrothermal technology and characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), and FT-IR spectroscopy. These phosphors present fusiform-like polyhedron microcrystals with tetragonal zircon structure and average particle size of about 300 nm. The luminescent properties of the three lanthanide ions activated GdVO₄ submicrometer phosphors are studied, which show the characteristic multicolor luminescence of Sm³⁺ (orange), Dy³⁺ (light yellow) and Er³⁺ (green) ions in visible region.     

Tunable luminescence and energy transfer properties in YVO<Subscript>4</Subscript>:Bi<Superscript>3+</Superscript>,Ln<Superscript>3+</Superscript> (Ln = Dy,Sm, Eu) phosphors prepared by microwave sintering method

YVO₄:Bi³⁺,Ln³⁺ (Ln?=?Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y³⁺. Under 275 nm excitation, the luminescent intensity of YVO₄:Bi³⁺ samples reach the maximum when Bi³⁺ concentration is 0.02, the broad excitation spectrum of YVO₄:Bi³⁺ has a strongest peak at near 343 nm. Doped Bi³⁺ can effectively improve the emission intensity of YVO₄:Ln³⁺. The energy transfer mechanism of Bi³⁺?→?Ln³⁺ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (R_c) between Ln³⁺ and Bi³⁺ were calculated by concentration quenching method. Emitting color of YVO₄:Bi³⁺,Ln³⁺ phosphors were tunable by adjusting Ln³⁺ content. In a word, the material has a good application prospects on light emitting diodes.     

Inter- and Intra-granular Interactions of REBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript>, RE: Eu,Gd, Ho and Er

Here, the superconducting and AC/DC magnetic properties of REBa₂Cu₃O_7−δ (RE: Eu, Gd, Ho and Er) are investigated in order to understand the inter-granular and intra-granular behavior of these compounds. These compounds were prepared by standard solid-state reaction route. ErBa₂Cu₃O_7−δ (Er-123) and HoBa₂Cu₃O_7−δ (Ho-123) (consisting of heavier rare earth) show higher orthorhombic splitting in their XRD patterns than those observed for EuBa₂Cu₃O_7−δ (Eu-123) and GdBa₂Cu₃O_7−δ (Gd-123) (consisting of lighter rare earth). Even though Eu, Gd, Ho and Er are magnetic elements, substitution of these at Y site in Y-123 does not change the superconducting transition temperature (T _c). Er-123 and Ho-123 exhibit very sharp superconducting transition while Eu-123 and Gd-123 exhibit relatively broad transition with little hump at the lower part of transition close to the long-range superconducting state with zero resistance. In addition to that, Eu-123 and Gd-123 show relatively higher normal state resistivity than those of Er-123 and Ho-123. The AC susceptibility measurements reveal that these compounds possess different strength of inter-granular couplings. The hump in the superconducting transition of Eu and Gd is not due to the lack of inter-grain couplings in these samples because of having better grain connectivity in the samples as compared to other rare earth elements in REBa₂Cu₃O_7−δ system. Though intra-grain peak is insensitive to the applied magnetic field, inter-grain peak is sensitive to the applied magnetic field.     

Controllable synthesis and luminescence of YPO<Subscript>4</Subscript>:Ln<Superscript>3+</Superscript> (Ln = Eu and Sm) nanotubes

YPO₄:Ln³⁺ (Ln = Eu and Sm) nanotubes were synthesized by a precipitation process in the presence of SDS. The XRD results showed that all samples have a xenotime type tetragonal structure, indicating that doped rare earth ions have no influence on the phase. The SEM and TEM images showed that all samples are nanotubes. On basis of the morphology of samples and the properties of SDS, the possible formation mechanism was speculated. YPO₄:Eu³⁺ and YPO₄:Sm³⁺ nanotubes showed characteristic emission bands of Eu³⁺ and Sm³⁺ ions, respectively. For YPO₄:Eu³⁺/Sm³⁺ nanotubes, the codoping Sm³⁺ ions can enhance the emission intensity of Eu³⁺ ions.     

Preparation and luminescence properties of Y<Subscript>3−y</Subscript>Al<Subscript>5−x</Subscript>Ga<Subscript>x</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript><Subscript>y</Subscript> phosphors

Y_3?yAl_5?xGa_xO₁₂:Ce³⁺_y phosphors were prepared by high temperature solid state reaction method. The crystal structures, the influence of Ga³⁺ concentration on the photoluminescence (PL), cathodoluminescence, thermal stability and morphology of the phosphors were studied in detail. The results indicated that diffraction angle of the samples decreased gradually with the increase of Ga³⁺ ions content in XRD pattern. The emission peak of the spectra show a progressive blue-shift, the intensity increased first and then decreased and the optimal Ga³⁺ concentration in Y_2.94Al_5?xGa_xO₁₂:Ce³⁺_0.06 phosphors is x?=?0.75. The critical concentration of Ce³⁺ in YAGG:Ce³⁺ phosphors is affected with the ratio of Ga³⁺ to Al³⁺ and the Y_2.9Al_4.25Ga_0.75O₁₂:Ce³⁺_0.1 phosphor showed the best performance on PL. However, the optimum concentration of Y_3?yAl_5?xGa_xO₁₂:Ce³⁺_y phosphors is x?=?1.5 and y?=?0.04 when they were excited by cathode ray.     

Tunable luminescence and energy transfer properties of Sr₃AlO₄F:RE³+ (RE = Tm/Tb, Eu, Ce) phosphors

Sr(3)AlO(4)F:RE(3+) (RE = Tm/Tb, Eu, Ce) phosphors were prepared by the conventional solid-state reaction. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectra, as well as lifetimes were utilized to characterize samples. Under the excitation of UV light, Sr(3)AlO(4)F:Tm(3+), Sr(3)AlO(4)F:Tb(3+), and Sr(3)AlO(4)F:Eu(3+) exhibit the characteristic emissions of Tm(3+) ((1)D(2)→(3)F(4), blue), Tb(3+) ((5)D(4)→(7)F(5), green), and Eu(3+) ((5)D(0)→(7)F(2), red), respectively. By adjusting the doping concentration of Eu(3+) ions in Sr(3)AlO(4)F:0.10Tm(3+), 0.10Tb(3+), zEu(3+), a white emission in a single composition was obtained under the excitation of 360 nm, in which an energy transfer from Tb(3+) to Eu(3+) was observed. For Sr(3)AlO(4)F:Ce(3+),Tb(3+) samples, the energy transfer from Ce(3+) to Tb(3+) is efficient and demonstrated to be a resonant type via a dipole-quadrupole interaction by comparing the experimental data and theoretical calculation. Furthermore, the critical distance of the Ce(3+) and Tb(3+) ions has also been calculated to be 9.05 ?. The corresponding luminescence and energy transfer mechanisms have been proposed in detail. These phosphors might be promising for use in near-UV LEDs.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Microwave dielectric properties of novel rare earth based silicates: RE<Subscript>2</Subscript>Ti<Subscript>2</Subscript>SiO<Subscript>9</Subscript> [RE = La,Pr and Nd]

The RE₂Ti₂SiO₉ [RE = La, Nd and Pr] ceramics are synthesized by solid state ceramic route. These materials exhibit a relative permittivity of about 30 with quality factor in the range 19,600–33,700 GHz. They also showed relatively low values of τ_f. The microwave dielectric properties of these materials are studied for the first time. The La_2−xPr_xTi₂SiO₉ [x = 0–2] based solid solution are also synthesized and single phase is confirmed over the whole composition range. The lattice parameters showed a linear variation with increasing x which can be well correlated with the ionic radius of the RE³⁺ ions.     

Sol-gel synthesis and photoluminescence of CaTi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>: Pr<Superscript>3+</Superscript> phosphors

CaTi_1−x Zr _x O₃: Pr³⁺ phosphors have been synthesized by sol-gel and solid state methods, with x = 1/300, 2/300, 3/300, 4/300, 5/300, 6/300, 7/300, respectively. Powder X-ray diffraction (XRD), UV-visible absorption spectra, photoluminescent spectra (PL), and scanning electron microscopy (SEM) images are used to characterize the powder samples. The inverse absorption at 610 nm appearing in the UV-visible absorption spectra is due to the ¹ D ₂ → ³ H ₄ characteristic emission of Pr³⁺. Changes in the emission spectra at 610 nm were agreed with those in UV-visible absorption spectra. The strongest red excitation obtained from CaTi_1−x Zr _x O₃: Pr³⁺ (x = 4/300) and CaTi_1−x Zr _x O₃: Pr³⁺ (x = 5/300) possesses the strongest emission at 610 nm, similar to the intensities of Ca(Ti_1−x Zr _x )O₃: Pr³⁺ (x = 3/300, 4/300, 6/300), which may be corresponded to the cell parameters of CaTi_1−x ZrxO₃: Pr³⁺.     

Tunable luminescence of Sr<Subscript>5(1−x)</Subscript>Ba<Subscript>5x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>Cl:Eu<Superscript>2+</Superscript> (0 ≤ x ≤ 100%) phosphors from different Eu<Superscript>2+</Superscript> centers

In this paper, a series of Eu²⁺ activated Sr_5(1?x)Ba_5x(PO₄)₃Cl (0?≤?x?≤?100%) phosphors were prepared by solid-state reaction method, and their luminescence properties under near-ultraviolet excitation were investigated. For Eu²⁺-activated Sr₅(PO₄)₃Cl, a strong emission band located at 445 nm is observed upon 365 nm excitation, which could be attributed to the 4f ⁶5d ¹–4f ⁷ transition of different Eu²⁺ centers. When the Ba²⁺ is introduced into the Sr₅(PO₄)₃Cl:Eu²⁺, the emission band of Eu²⁺ is broadened largely. The fluorescence lifetimes for different Eu²⁺ centers were determined by the decay curves and time-resolved spectra. The excitation spectra of the as-prepared samples cover a wide wavelength range from 240 to 420 nm, which can well match the emission wavelength of the near ultraviolet LED chip. The investigation of the thermal luminescence stability reveals that the introduction of Ba²⁺ could improve the thermal quenching properties.     

Synthesis of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphor in the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al metal–CeO<Subscript>2</Subscript> ternary system

Garnet phosphor Y₃Al₅O₁₂:Ce³⁺ is prepared in the Y₂O₃–Al metal–CeO₂ ternary system by the solid-state reaction method in the air. For the first time, metal Al is used as a source of aluminum for the reaction instead of traditional oxide Al₂O₃. It is shown that the chemical reaction can be realized at lower temperatures and without use of special reducing atmosphere. The structural and spectroscopic properties of the prepared powder phosphor are very close to those earlier reported for the Y₃Al₅O₁₂:Ce³⁺ single crystal.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er<Superscript>3+</Superscript>,Ce<Superscript>3+</Superscript>—A new “invisible” IR phosphor

Ce³⁺ doping of Y₂O₂S:Er³⁺ can be used to suppress the visible anti-Stokes luminescence of the phosphor under excitation in the range 0.90–0.98 μm. We take advantage of this effect to create a new, efficient “invisible” IR phosphor emitting in the range 1.5–1.6 μm.     

Luminous properties of skin–core structure new luminous fiber: SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,Dy<Superscript>3+</Superscript>-PET/light conversion agent-PET

SrAl₂O₄:Eu²⁺,Dy³⁺-polyethylene terephthalate (PET)/light conversion agent-PET, which is a new skin–core structure luminous fiber that can emit red light in the darkness, was fabricated by melt spinning with the combination of light conversion agent-PET and SrAl₂O₄:Eu²⁺,Dy³⁺-PET. An energy transfer occurred between SrAl₂O₄:Eu²⁺,Dy³⁺ and light conversion agent, and the light conversion agent emitted red light absorbed from SrAl₂O₄:Eu²⁺,Dy³⁺. To investigate the effect of light conversion agent on the luminous properties of SrAl₂O₄:Eu²⁺,Dy³⁺-PET-light conversion agent, several kinds of luminous fiber that contained different light conversion agents were artificially manufactured and their luminous properties were investigated. Results showed that under near-ultraviolet excitation, the fluorescent color of luminous fiber was primarily located in the orange-red area, with more intense red color than the others.     

Controllable synthesis and luminescence property of LnPO<Subscript>4</Subscript> (Ln = La,Gd, Y) nanocrystals

Lanthanide orthophosphate LnPO₄ (Ln = La, Gd, Y) nanocrystals with different crystalline structures and morphologies were synthesized successfully by a hydrothermal method under mild conditions. The obtained LaPO₄ have a monoclinic or hexagonal structure with varying the temperature. However, as to GdPO₄ and YPO₄, the temperature has no obvious effect on their structures. By tuning the amount of cetyltrimethylammonium bromide (CTAB), the morphology and size of all samples can be controlled easily and effectively. Noticeably, the structure of YPO₄ can also be controlled by using the CTAB. A systematic study of the photoluminescence in Ln³⁺-doped lanthanide phosphates shows that the luminescent properties of these nanophosphors are strongly dependent on their crystal structures and morphologies.     

Color-tunable luminescence by energy transfer mechanism in RE (RE = Eu2+, Tb3+)–doped Na2SrPO4F phosphors

Journal of Materials Science: Materials in Electronics - In the current research work, Eu2+, Tb3+ singly doped and co-doped Na2SrPO4F phosphors have been synthesized by solid-state reaction method...