Single-phased Phosphor Research Articles

Synthesis, luminescent properties and energy transfer in Tb3+ and Eu3+ co-doped Li3Ba2Gd3 (MoO4)8 phosphors for W-LED’s

For the first time, single phase monoclinic Li3Ba2Gd3 (MoO4)8: 0.08 Tb3+,yEu3+ (0, 0.005, 0.02, 0.04, 0.06, 0.08 and 0.10 mol) nano phosphors were prepared by the simple mechanochemically assisted direct solid state reaction method at room temperature. Their crystal structures, luminescence properties, energy transfer mechanism and life time were studied in detail. At the excitation wavelength of 378 nm, the emission spectra of Li3Ba2Gd3 (MoO4)8: 0.08 Tb3+,yEu3+ (0, 0.005, 0.02, 0.04, 0.06, 0.08 and 0.10 mol) phosphors exhibit the characteristic emissions of Tb3+ and Eu3+ ions at around 545, 594 and 615 nm due to energy transfer from Tb3+ ions to Eu3+ ions. It is confirmed from the results that electric dipole–dipole interaction phenomena is the main cause for having energy transfer from Tb3+ to Eu3+ ions in Li3Ba2Gd3 (MoO4)8 host. The CIE coordinates of the prepared nano phosphors illustrate that by changing the ratio of Eu3+ ions the white light emission can be realized from Li3Ba2Gd3 (MoO4)8 phosphor and it coexist very close to an ideal white chromaticity coordinates (0.33, 0.33). All properties show that Li3Ba2Gd3 (MoO4)8: 0.08 Tb3+, 0.005 Eu3+ nano phosphor is a promising material for single-phase phosphor based white light emitting diodes.

Triple energy transfer and color tuning in Tb3+ and Eu3+-coactivated apatite-type gadolinium-containing phosphors

A family of apatite-type fluorophosphate phosphors with general formula Sr3Gd(1-m-n)Na(PO4)3F:mTb3+,nEu3+ (SGN:mTb3+,nEu3+) have been synthesized via the high-temperature solid-state reaction method. Triple energy transfer processes from Gd3+ in the host to both Tb3+ and Eu3+, as well as from Tb3+ to Eu3+ have been verified by the photoluminescence spectra. Under the excitation of UV light, both green line from the transitions of Tb3+ and red line origin from the transitions of Eu3+ have been simultaneously observed in a single phase phosphor, which makes a promise for tunable color emissions from yellowish-green through yellow and ultimately to reddish-orange by simply adjusting the Eu3+ content (n) in SGN:0.20Tb3+,nEu3+ phosphors. Additionally, the energy transfer from the Tb3+ to the Eu3+ ions has been demonstrated to be a resonant type via a quadrupole–quadrupole mechanism based on the Dexter's theoretical model, and the energy transfer efficiency increases with an increase in Eu3+ concentration.

Luminescence properties of emission tunable single-phased phosphor La7O6(BO3)(PO4)2: Ce3+, Tb3+, Eu3+

Abstract Emission color tunable single-phased phosphors La 7 O 6 (BO 3 )(PO 4 ) 2 : Ce 3+ , Tb 3+ , Eu 3+ were prepared by a solid state reaction method. The crystal structure, luminescence properties, energy transfer, and co-excitation behavior were investigated in detail. The La 7 O 6 (BO 3 )(PO 4 ) 2 : x Ce 3+ phosphors emit blue light under the excitation at 228 nm, corresponding to the broad 4f-5d transition of Ce 3+ . Concentration quenching phenomenon was observed when the Ce 3+ ion was x = 0.01. By co-doping the Eu 3+ and Tb 3+ ions into La 7 O 6 (BO 3 )(PO 4 ) 2 : Ce 3+ phosphors, the emission color can be tunable from blue to reddish, and then to white. The energy transfer from Ce 3+ to Eu 3+ and the co-excitation of Ce 3+ and Tb 3+ have been investigated and discussed. The color coordinate for the La 7 O 6 (BO 3 )(PO 4 ) 2 : 0.01Ce 3+ , 0.05Tb 3+ , 0.05Eu 3+ phosphor is calculated to be (0.3008, 0.3381).

Experimental study and thermodynamic calculation of Lu2O3-SiO2 binary system

Abstract As a binary system of BaO-Lu 2 O 3 -SiO 2 ternary system, Lu 2 O 3 -SiO 2 system was optimized and calculated by CALPHAD approach based on available phase diagram and relevant thermodynamic data of RE 2 O 3 -SiO 2 (RE=Lu, Yb, Y) binary systems as well as our experimental data of Lu 2 O 3 -SiO 2 system obtained by quenching experiment. The Gibbs free energy of high temperature solution was described by an ionic two-sublattice model as (Lu 3+ ) P (O 2– , SiO 2 0 ) Q . The calculated phase diagram below 1873 K was in good agreement with experimental data at 1573, 1773 and 1873 K. The calculated Gibbs energies of two intermediate phases Lu 2 SiO 5 and Lu 2 Si 2 O 7 , the activity of Lu 2 O 3 and SiO 2 and specific heat capacities of intermediate phases agreed well with experimental results of Y 2 O 3 -SiO 2 system. This tentative study will offer help for the research of single-phase phosphor and related metallurgical slags, refractories, high-temperature superconductivity material systems.

Color tunable and white light emitting via energy transfer in single-phase BiOCl:Er3+,Sm3+ phosphors for WLEDs

Abstract BiOCl crystal shows potential as efficient optical host due to its special layered structure. Here, the luminescence properties of the Er3+/Sm3+ co-doped BiOCl phosphors as single-phase phosphors were reported. Upon near ultraviolet excitation (NUV, 380 nm corresponding the 4I15/2 → 4G11/2 transition of Er3+ ions), the phosphors exhibit the efficient characteristic emissions of Er3+ and Sm3+ ions simultaneously. The energy transfer (ET) from Er3+ to Sm3+ ions in the layered crystals has been validated by the variation of emission intensities and decay lifetimes respectively, which is ascribed to be a dipole–dipole interaction. By virtue of the ET behavior and increasing Sm3+ ion concentration, the enhancing emission intensity of Sm3+ and the tunability of emission color from yellowish-green (0.318, 0.420) to white (0.343, 0.347) are realized. The results of our work indicate that the Er3+/Sm3+ co-doped BiOCl phosphor has a promising application serving as single component white emitting phosphors for NUV excited WLEDs.

Facile ultrasound route for the fabrication of green emitting Ba2SiO4:Eu2+ nanophosphors for display and dosimetric applications

Abstract A series of Eu 2+ (1–5 mol%) activated Ba 2 SiO 4 nanophosphors were prepared by ecofriendly ultrasound assisted sonochemical route using Epigallocatechin gallate (EGCG) extract as bio-surfactant. The obtained nanophosphors were well characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) etc. The average crystallite size was estimated using Debye–Scherer's formula and Williamson–Hall (W–H) plots and were found to be in the range 20–32 nm. The photoluminescence excitation spectrum exhibited two broad bands around 330 and 370 nm ascribed to the transitions of Eu 2+ from 4f-ground state to 5d-excited state. The emission spectra showed broad band around 505 nm wavelength ascribed to 5d → 4f allowed transition of Eu 2+ ions. Thermoluminescence (TL) of Eu 2+ doped Ba 2 SiO 4 nanophosphors were investigated using γ-irradiation in the dose range1–6 kGy at a warming rate of 5 °C min −1 . The phosphors show a well resolved single glow peak at ∼175 °C. The TL intensity of 155 °C glow peak increase linearly with γ-dose and room temperature fading was ∼76% which was highly useful in radiation dosimetry. The kinetic parameters ( E , s ) were estimated and the results were discussed. The chromaticity co-ordinates of all the prepared phosphors were located in green region, as a result Eu 2+ activated Ba 2 SiO 4 was a promising single phased phosphor for WLEDs.

Enhanced photoluminescence property and broad color emission of ZnGa2O4 phosphor due to the synergistic role of Eu3+ and carbon dots

Abstract ZnGa 2 O 4 phosphors co-composited with nanoscale carbon dots (CDs) and Eu 3+ were presented for the tunable color emission. Novel single phase CDs or/and Eu 3+ composited ZnGa 2 O 4 phosphors were synthesized by microwave hydrothermal method and their optical properties were investigated. The ZnGa 2 O 4 phosphors composited with CDs exhibited an intense broad blue light emission at 421 nm and a more enhanced photoluminescence intensity than those without CDs. The Eu 3+ composited ZnGa 2 O 4 phosphors gave an ideal red color emission. The CDs/Eu 3+ co-composited ZnGa 2 O 4 phosphors exhibited a wide emission band peak at 450 nm and narrow emission peak at 618 nm. Furthermore, the tunable color emissions of CDs/Eu 3+ co-composited ZnGa 2 O 4 phosphors from blue to the white light region, and then to red were obtained with the increasing Eu 3+ concentration, which can be a promising single phased phosphor candidate in light emitting diodes. Broadly tunable emission single phased phosphor is tuned firstly through the synergistic role of the non-metal element and the rare earth metal ions.

Effect of crystal structures on energy transfer behavior from Bi3+ to Eu3+ in alkaline earth metalstannates

Abstract A single phased color-tunable phosphor via energy transfer has drawn much attention, whereas it is still a question that how to choose a suitable host to realize an efficient energy transfer. In this work, novel single Bi 3+ or Eu 3+ doped and Bi 3+ , Eu 3+ co-activated Ca 2 SnO 4 (CSO) and Sr 2 SnO 4 (SSO) phosphors have been prepared through a high temperature solid state reaction. The energy transfer happening from hosts to Eu 3+ has been confirmed. By co-doping of Bi 3+ , a brighter red light is realized which is attributed to the much more efficient energy transfer from Bi 3+ to Eu 3+ . After comparison, the energy transfer efficiency from Bi 3+ to Eu 3+ is much higher in CSO:Bi 3+ , Eu 3+ than that in SSO:Bi 3+ , Eu 3+ . Furthermore, the experiment reveals that the single-phased color-tunable phosphors exhibit excellent resistance against thermal quenching, suggesting that they can be potential candidates in UV-pumped white light emitting diodes (LEDs).

Tunable-emission single-phase phosphors Ba3Ca2(PO4)3F:M (M=Ce3+, Eu2+, Mn2+): Crystal structure, luminescence and energy transfer

Abstract A series of single-phase phosphors Ba3Ca2(PO4)3F:M (M = Ce3+, Eu2+, Mn2+) are prepared through a high temperature solid state method, and the luminescence properties and the energy transfer mechanisms from Ce3+ to Eu2+, Ce3+ to Mn2+, and Eu2+ to Mn2+ are investigated in detail. Ce3+, Eu2+ or Mn2+ single doped Ba3Ca2(PO4)3F can produce blue, green and orange-red emission, respectively. An effective energy transfer from Ce3+ to Eu2+ and from Ce3+/Eu2+ to Mn2+ occurs in Ba3Ca2(PO4)3F, and the emission color can change from blue to green, blue to red, green to yellow, and red to yellow in Ce3+/Eu2+, Ce3+/Mn2+, Eu2+/Mn2+ and Ce3+/Eu2+/Mn2+ doped Ba3Ca2(PO4)3F, respectively. Moreover, for Ba3Ca2(PO4)3F: Eu2+, Eu2+ ions prefer to occupy the M2 sites at low concentration, and then partially occupy the M1 sites with the concentration increasing, and the energy transfer from Eu2 (M2) to Eu1 (M1) sites are conformed. For Ba3Ca2(PO4)3F:0.03Eu2+, zMn2+, Eu2+ ions tend to be Eu3+ with increasing Mn2+ concentration due to the energy transfer from Eu2+ to Mn2+.

Single phase GdPO4: Dy3+ microspheres blue, yellow and white light emitting phosphor

Abstract Luminescent microspheres, Gd (1−x) Dy x PO 4 have been synthesized using simple combustion method for the first time. SEM images show that the obtained powders are formed by dispersed microscaled spheres with diameter ranging from 0.5 to 1 μm. The X-ray diffraction, FTIR and Raman spectroscopy studies reveal that the microparticles annealed at 800 °C crystallized in a monoclinic phase with space group P2 1 /n. Under host Gd 3+ sensitization, Gd (1−x) Dy x PO 4 emission spectra of Dy 3+ show a broad blue band attributed to transitions 4 I 15/2 + 4 I 13/2 + 4 I 11/2 + 4 F 9/2 → 6 H 15/2 , a sharp yellow band due to 4 F 9/2 → 6 H 13/2 transition, and the little red band of 4 F 9/2 → 6 H 11/2 transition. Blue and white emissions have been obtained at low and high Dy 3+ concentration, respectively due the energy transfer from Gd 3+ to Dy 3+ . Under direct 4f–4f excitation of Dy 3+ in GdDPO 4 , three bands attributed to 4 F 9/2 → 6 H 15/2 , 6 H 13/2 , 6 H 11/2 transitions have been observed resulting in a yellow light emission. The emission bands intensity are discussed as function of GdPO 4 structure. They are in well agreement with crystal structure of the host lattice GdPO 4 in contrast to reported works. The decay rates for the 4 F 9/2 level are found to be deviated from exponential to non-exponential nature with increase of Dy 3+ concentration. A promising white-light emission for white LED operating under UV excitation is investigated from single-phased phosphor. The obtained results suggest a potential application of GdPO 4 :Dy 3+ microspheres as alternatives to replace bulk materials for many application fields, including light display systems and optoelectronic devices.

Luminescence properties of silicate apatite phosphors M2La8Si6O26:Eu (M = Mg, Ca, Sr)

Abstract Europium ions doped M2La8Si6O26 (M = Mg, Ca, Sr) silicate apatite phosphors have been synthesized by using solid-state reaction method, post-treated in a reducing atmosphere and studied by optical spectroscopy techniques. It has been revealed that the emission spectra from all the synthesized samples contain a set of spectral lines due to the 4f – 4f transitions of Eu3+ ions, which predominantly occupy the A2 sites of Cs symmetry in the apatite structure. Efficient conversion of Eu3+ to Eu2+ has been achieved in a reducing H2/Ar atmosphere for the Mg2La8(SiO4)6O2 apatite due to the charge compensation mechanism by oxygen vacancies. This apatite possesses broadband yellow emission with the band maximum at 560 nm and the luminescence decay time τ

Versatile host-sensitized white light emission in a single-component K3ZnB5O10:Dy3+ phosphor for ultraviolet converted light-emitting diodes

Abstract A single-phase white-light-emitting phosphor, K3ZnB5O10:Dy3+, has been synthesized by a conventional solid-state reaction method. X-ray diffraction (XRD) analysis was used to determine the monoclinic crystal structure of phosphors. The surface states, B 1s, O 1s, K 2p, Zn 2p, and Dy 3d of the phosphor was quantified by X-ray photoelectron spectroscopy (XPS). Diffuse reflectance spectroscopy (DRS) revealed double absorption edges at 3.27 and 5.46 eV for K3ZnB5O10 matrix. The formation of defect-levels, zinc interstitials ( Z n i ) , zinc vacancies ( V Z n ) , oxygen antisites ( O Z n ) and oxygen vacancies ( V O ) in K3ZnB5O10:Dy3+ phosphors were identified by photoluminescent (PL) spectroscopy. The emissions at 405 nm (violet-I), 434 nm (violet-II), and 467 nm (blue) are due to intra-band transitions of ( F X → V Z n ) , ( Z n i → V Z n ) and ( Z n i → O Z n ) of the host, respectively. Similarly, the emission at 517 nm (green) corresponds to the transition from free excitons to the oxygen vacancies in the host ( F X → V O ) . The emissions at 575 and 665 nm are assigned to the f-f transitions of Dy3+ ions within the host matrix. An energy level diagram is proposed to describe the host emission and possible energy transfer from the host to dopant ions in the single-phase phosphor. The phosphor shows good thermal stability with activation energy of 0.52 eV. The combined emissions in the blue, green, yellow, and red regions resulted in white light emission with CIE coordinates of (0.256, 0.258) on the CIE diagram.

Emission color tuning through manipulating the energy transfer from VO43− to Eu3+ in single-phased LuVO4:Eu3+ phosphors

Recently, rare earth (RE) ion doped single-phased phosphors, which can emit tunable colors upon single wavelength excitation, have received a great deal of attention, but most of them involve multiple dopants as luminescence centers.

Luminescence and energy transfer of color-tunable Na6Ca3Si6O18:Ce3+,Tb3+ phosphors for WLED

Abstract A series of Ce 3+ , Tb 3+ co-doped Na 6 Ca 3 Si 6 O 18 phosphors have been synthesized by traditional solid state reaction. The emission spectra of the Na 6 Ca 3 Si 6 O 18 :Ce 3+ ,Tb 3+ phosphors show a blue broad band at 450 nm of the Ce 3+ and a green line peaking at 550 nm. Energy transfer from Ce 3+ to Tb 3+ ions has been investigated. Results indicate that the color of these phosphors changes from blue to green by adjusting the ratio of Ce 3+ to Tb 3+ . In addition, the mechanism of the energy transfer from the Ce 3+ to Tb 3+ ions is demonstrated to be a dipole-quadrupole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. By optimizing the Tb 3+ concentration, the absolute PL quantum yield as high as 43% can be achieved. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.

Luminescence characterization of Dy and Eu doped Na6 Mg(SO4 )4 phosphors.

A series of single-phase phosphors based on Na6 Mg(SO4 )4 (Zeff =11.70) doped with Dy and Eu was prepared by the wet chemical method. The photoluminescence (PL) and thermoluminescence (TL) properties of Dy3+ - and Eu3+ -activated Na6 Mg(SO4 )4 phosphors were investigated. The characteristic emissions of Dy3+ and Eu3+ were observed in the Na6 Mg(SO4 )4 host. The TL glow curve of the Na6 Mg(SO4 )4 :Dy phosphor consisted of a prominent peak at 234°C and a very small hump at 158°C. The TL sensitivity of the Na6 Mg(SO4 )4 :Dy phosphor was found to be four times less than the commercialized CaSO4 :Dy phosphor. The TL dose-response of the Na6 Mg(SO4 )4 :Dy phosphor was studied from a dose range of 5-10kGy and the linear dose-response was observed up to 1kGy which is good for a microcrystalline phosphor. Trapping parameters for both the samples were calculated using the Initial Rise and Chen's peak shape methods.

Monodispersed spherical YAG:Ce3+ phosphor particles by one-pot synthesis

Monodispersed spherical Ce3+-doped yttrium aluminum garnet phosphors were prepared by novel one-pot synthetic method designed. The morphology and size of phosphor particles were controlled by changing the solvent composition and the concentration of metal ion components. Single-phased phosphors with spherical shape and good dispersity could be achieved by firing the precursors at relatively low temperature. From the photoluminescence spectra, it was confirmed that the synthesized YAG:Ce3+ phosphor emits typical yellow-green light peaked at around 540 nm under an excitation of 468 nm-wavelength. For white emission, on the other hand, the pc-WLED using the synthesized YAG:Ce3+ phosphor and blue LED chip was fabricated and its electroluminescent property was evaluated.

Warm white light generation from single phase Sr3Y(PO4)3:Dy3+, Eu3+ phosphors with near ultraviolet excitation

Abstract Novel Sr3Y(PO4)3:Dy3+, Eu3+ (SYP:Dy3+, Eu3+) phosphors were synthesized by a standard solid-state reaction under an ambient air atmosphere and their structural and optical properties were investigated. XRD and diffuse reflectance spectra (DRS) were used to explore structural properties. The former showed that single phase phosphors were obtained and that the rare earth ions entered into the cubic host by substituting the smaller Y3+ ions and thereby enlarging the unit cell. The DRS indicated that the host has a direct bandgap of 4.5 eV. Under 393 nm excitation, a strong and stable warm white light emission with high color purity was achieved in SY0.92P:0.06Dy3+, 0.04Eu3+. The energy transfer from Dy3+ to Eu3+ ions was investigated and the related mechanism was discussed based on the optical spectra and emission decay curves. The thermal quenching of emission is similar to that of YAG:0.06Ce3+. The results show the single phase phosphor is potential in warm white LED.

Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs).

Preparation and luminescence properties of color-tunable single-phased LaPO4:Eu3+/Tb3+ phosphors

A novel series of color-tunable single-phased phosphors La1–x–yPO4:xEu3+/yTb3+(x=0, 0.01, 0.02, 0.03, 0.04, 0.05; y=0, 0.05, 0.10, 0.15, 0.20) was synthesized via co-precipitation method with diammonium hydrogen phosphate as precipitant. The morphology, crystal structure and photoluminescence properties of the as-prepared samples were characterized by means of X-ray diffraction(XRD), scanning electron microscopy(SEM) and fluorescence spectrophotometer. The results reveal that the as-synthesized samples calcined at 1100 °C display spherical morphology with uniform distribution. Upon excitation with 350 nm ultraviolet radiation, the LaPO4:Eu3+/Tb3+ phosphors showed a green light peaking at 543 nm assigned to the characteristic 5D4-7F5 emission of Tb3+ and a red light peaking at 591 nm corresponding to the characteristic 5D0-7F1 emission of Eu3+ simultaneously. For the Eu3+/Tb3+ co-activated phosphors, Tb3+ acts as an efficient sensitizer to enhance the emission intensity of Eu3+ ions. The energy transfer mechanism and the emission color tunability of LaPO4:Eu3+/Tb3+ have been studied. The results indicate that a color-tunable luminescence(from green to white to red) can be achieved by adjusting the Eu3+/Tb3+ doping ratio in the LaPO4 host matrix.

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