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DOE OSTI2012

Tuning of crystal phase and luminescence properties of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} phosphors

Graphical abstract: The optical properties of Dy{sup 3+} were found to be sensitive to the crystal phase of the as-synthesized Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} phosphors, especially the distinct features of the charge transfer (CT) transition. The mechanism involved was discussed in detail based on the experiments and theoretic calculations. Highlights: ► The crystal phase of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} was tuned by changing the pH value of the solution in hydrothermal system. ► The optical properties of Dy{sup 3+} were found to be sensitive to the crystal phase of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+}. ► The mechanisms of different crystal phases affected on the luminescence properties of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} were discussed. -- Abstract: The orthorhombic and monoclinic Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd{sub 2}(MoO{sub 4}){sub 3}:Dy{sup 3+} were discussed. The electric dipole–dipole interaction between Dy{sup 3+} ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd{sub 1.84}(MoO{sub 4}){sub 3}:Dy{sub 0.16}{sup 3+} can be considered as a suitable candidate for white light emitting diodes (W-LEDs).

36 MATERIALS SCIENCE↗

DOE OSTI2012

Effect of cerium on structure modifications of a hybrid sol–gel coating, its mechanical properties and anti-corrosion behavior

Highlights: ► New sol–gel routes to replace chromates for corrosion protection of aluminum. ► Effect of cerium concentration on the microstructure of xerogel. ► Electrochemical and mechanical performances of hybrid coating with different cerium contents. ► Good correlation between the different results with an optimal cerium content of 0.01 M. -- Abstract: An organic–inorganic hybrid coating was developed to improve the corrosion resistance of the aluminum alloy AA 2024-T3. Organic and inorganic coatings derived from glycidoxypropyl-trimethoxysilane (GPTMS) and aluminum tri-sec-butoxide Al(O{sup s}Bu){sub 3}, with different cerium contents, were deposited onto aluminum by dip-coating process. Corrosion resistance and mechanical properties were investigated by electrochemical impedance measurements and nano-indentation respectively. An optimal cerium concentration of 0.01 M was evidenced. To correlate and explain the hybrid coating performances in relation to the cerium content, NMR experiments were performed. It has been shown that when the cerium concentration in the hybrid is higher than 0.01 M there are important modifications in the hybrid structure that account for the mechanical properties and anti-corrosion behavior of the sol–gel coating.

36 MATERIALS SCIENCE↗

DOE OSTI2013

A novel red emitting phosphor of Eu{sup 3+} doped TTB-type niobate NaSr{sub 2}Nb{sub 5}O{sub 15} for white LEDs

Highlights: ► A novel red phosphor NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} was synthesized and investigated firstly. ► Crystal structure and characteristic luminescence properties are discussed. ► The charge compensation mechanism is also investigated. ► The intensity of NSN:0.03Eu{sup 3+}, 0.03Li{sup +} is 64.5% of the commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. ► It has good color saturation, the CIE is closed to that of commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. - Abstract: Eu{sup 3+} doped NaSr{sub 2}Nb{sub 5}O{sub 15} series were firstly synthesized by solid-state reaction method. Crystal structure, characteristic luminescence properties as well as charge compensation mechanism are investigated detailedly by X-ray diffraction refinement and photoluminescence spectra measurement. NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} exhibits strong absorption in near ultraviolet-blue region and intense red emission with CIE chromaticity coordinates (0.638, 0.355) after adding the charge compensation agent upon 398 nm excitation. The integral intensity of NSN:0.03Eu{sup 3+}, 0.03Li{sup +} is 64.5% of the commercial Y{sub 2}O{sub 3}:Eu{sup 3+} and the quantum efficiency is calculated to be 41.5%. The results show that NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} can be a promising red-emitting phosphor for white LEDs.

36 MATERIALS SCIENCE↗

DOE OSTI2013

The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction

Graphical abstract: This paper describes: The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction. The emission intensity of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux is enhanced as the sintering temperature was increased from 800 °C to 1000 °C and reveals the maximum value at 1000 °C. Photoluminescence emission spectra of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature for 3 h via solid state reaction method (λ{sub ex} = 270 nm). Highlights: ► NH{sub 4}Cl flux is helpful for enhancing the crystallization degree and decreasing surface defects. ► A single phase of NaCaPO{sub 4}:Eu{sup 3+} phosphor was observed as the sintering temperature was increased from 800 °C to 1000 °C. ► The intensity of the excitation peaks displays a maximum value at 1000 °C. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect the morphology. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect fluorescent properties. - Abstract: NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature (800, 900, 1000, 1100 °C) for 3 h under air atmosphere were synthesized successfully via solid state reaction method. It is found that the addition of NH{sub 4}Cl flux and different sintering temperatures can affect the morphology and fluorescent properties of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphor. The X-ray diffractions show a single phase and the microstructure observations show uniform morphologies for NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors sintered at the range from 900 °C to 1000 °C, indicating that addition of 2 wt.% NH{sub 4}Cl flux is helpful for enhancing the crystallization, thus improving the luminescence intensity of the charge transfer transition. The intensity of the excitation peaks displayed a maximum value at 1000 °C. The chromaticity (x, y) is in the orange-red region (0.54, 0.39) and the lifetime value is about 2.1 ms, suitable for the remote phosphor packages.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Spectral investigations of Sm{sup 3+}-doped oxyfluorosilicate glasses

Graphical abstract: The figure shows the emission spectra of Sm{sup 3+} doped KNSZL glass for different concentrations. Among the four emission transitions {sup 4}G{sub 5/2} → {sup 6}H{sub 5/2}, {sup 4}G{sub 5/2} → {sup 6}H{sub 7/2}, {sup 4}G{sub 5/2} → {sup 6}H{sub 9/2} and {sup 4}G{sub 5/2} → {sup 6}H{sub 11/2}, the {sup 4}G{sub 5/2} → {sup 6}H{sub 7/2} transition of KNSZLSm10 glass is more intense compared with all the transitions. The insert figure shows, the color coordinates (0.59, 0.41) of KNSZLSm10 glass is located on the perimeter of the chromaticity diagram at 592 nm which appears to be closest to the orange color. From these results the KNSZLSm10 glass could be useful for optical amplifiers, waveguides, telecommunications and orange LEDs. - Highlights: • From the DTA, the undoped KNSZL glass more precisely in fiberdrawing. • The XRD pattern confirmed the KNbO{sub 3} nanocrystallites of undoped KNSZL glass. • FTIR and Raman data of KNSZLSm10 glass revealed structural properties. • Judd–Ofelt analysis and decay measurements were carried out. • The optical gain parameter of the investigated glass is 18.13 × 10{sup −25} cm{sup 2} s. - Abstract: Sm{sub 2}O{sub 3}-doped oxyfluorosilicate glasses were prepared by melt-quenching method. The differential thermal analysis and X-ray diffraction were carried out to investigate the glass transition temperature and structure of precursor glass. Infrared spectroscopy, Raman, optical absorption, photoluminescence and decay measurements were carried out for Sm{sup 3+}-doped oxyfluorosilicate glasses. From the absorption spectrum, the Judd–Ofelt intensity parameters have been evaluated to predict the radiative properties for the emission levels of Sm{sup 3+} ions. The lifetimes of {sup 4}G{sub 5/2} level are found to decrease from 1.17 to 0.93 ms due to the energy transfer, when the concentration of Sm{sup 3+} ions increases from 0.1 to 2.0 mol%. The optical gain parameter (18.13 × 10{sup −25} cm{sup 2} s) of the investigated glass is found to be higher than the other Sm{sub 2}O{sub 3}-doped glass systems.

36 MATERIALS SCIENCE↗

DOE OSTI2013

A novel red phosphor Ca{sub 12}Al{sub 14}O{sub 32}Cl{sub 2}:Eu{sup 3+} for near UV white light-emitting diodes

Graphical abstract: - Highlights: • Novel red phosphor Ca{sub 12}Al{sub 14}O{sub 32}Cl{sub 2}:Eu{sup 3+} was prepared by solid-state reaction. • Excitation spectra suggested an obvious absorption in near-ultraviolet region. • Under 392 nm excitation, the phosphors exhibited a red emission at 614 nm. • Ca{sub 12}Al{sub 14}O{sub 32}Cl{sub 2}:Eu{sup 3+} could be potentially applied in near UV white LEDs. - Abstract: A novel red phosphor Ca{sub 12}Al{sub 14}O{sub 32}Cl{sub 2}:Eu{sup 3+} was synthesized using a solid-state reaction method, and its luminescence characteristics and charge compensators effect (Li{sup +}, Na{sup +}, K{sup +}) were investigated. The excitation spectra showed a obvious absorption in near-ultraviolet region. Under 392 nm excitation, the phosphors exhibited an intense red emission at 614 nm. The Commission Internationale de l’Eclairage (CIE) chromaticity coordinates and quantum efficiency (QE) were (0.65, 0.35) and 62.3%, respectively. The good color saturation, high quantum efficiency and small thermal-quenching properties indicate that Ca{sub 12}Al{sub 14}O{sub 32}Cl{sub 2}:Eu{sup 3+} could be potentially applied in near UV white light-emitting diodes.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Temperature dependence of the luminescence of calcium-magnesium phosphate Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+}, a blue-emitting material for white light-emitting diodes

Graphical abstract: - Highlights: • Emission spectrum at 20 K confirms that Eu{sup 2+} ions occupy three sites. • Decay curves of three types of Eu{sup 2+} reflect the characteristics of energy transfer. • The Eu(I) emission is thermally quenched at 323 K. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} has good thermal stability. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} is a promising phosphor for near UV excited white LEDs. - Abstract: A blue-emitting phosphor Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} peaking at 450 nm was synthesized by a solid state reaction. The XRD patterns, luminescence properties, decay curves of samples as well as their thermal quenching and comparing the luminescence properties with that of commercial material were investigated. At 20 K, the emission spectrum exhibiting two distinct bands peaking at 437 and 473 nm with a shoulder peak at 510 nm can be attributed to the overlap of Eu(I), Eu(II) and Eu(III) emission bands. At 423 K the PL intensity decreases to 80% of the value at room temperature, and the emission wavelength shifts toward high energy. The derived activation energy indicates that the lowest energy level of the Eu{sup 2+} 4f{sup 6}5d{sup 1} state is well isolated from the host lattice conduction band. The PL spectra and chromaticity coordinates are close to those of BAM. Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} could be a potential candidate for near-UV excited white LEDs.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Comparison of structural and luminescence properties of Dy{sub 2}O{sub 3} nanopowders synthesized by co-precipitation and green combustion routes

Highlights: • Dy{sub 2}O{sub 3} nanopowders were prepared by co-precipitation and eco-friendly green combustion route using plant latex. • Both the products show excellent chromaticity coordinates in the white region, which were quite useful for white LED’s. • Thermoluminescence response of the Dy{sub 2}O{sub 3} product prepared by green synthesis was higher when compared to co-precipitation route. • Structural parameters of Dy{sub 2}O{sub 3} were estimated using Rietveld refinement. • The development of nanosize materials using eco-friendly resources was an attractive non-hazardous chemical route. - Abstract: Dysprosium oxide (Dy{sub 2}O{sub 3}) nanopowders were prepared by co-precipitation (CP) and eco-friendly green combustion (GC) routes. SEM micrographs prepared by CP route show smooth rods with various lengths and diameters while, GC route show porous, agglomerated particles. The results were further confirmed by TEM. Thermoluminescence (TL) responses of the nanopowder prepared by both the routes were studied using γ-rays. A well resolved glow peak at 353 °C along with less intense peak at 183 °C was observed in GC route while, in CP a single glow peak at 364 °C was observed. The kinetic parameters were estimated using Chen’s glow peak route. Photoluminescence (PL) of Dy{sub 2}O{sub 3} shows peaks at 481, 577, 666 and 756 nm which were attributed to Dy{sup 3+} transitions of {sup 4}F{sub 9/2}⟶{sup 6}H{sub 15/2}, {sup 6}H{sub 13/2}, {sup 6}H{sub 11/2} and {sup 6}H{sub 9/2}, respectively. Color co-ordinate values were located in the white region as a result the product may be useful for the fabrication of WLED’S.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Synthesis and photoluminescence properties of Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} red phosphor for white light emitting diodes

Highlights: • A novel red phosphor Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} was synthesized and investigated firstly. • The structure and characteristic luminescence properties are discussed. • The excellent thermal stability was found and investigated. • It has good color saturation, the CIE is close to that of commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. - Abstract: A series of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} red phosphors were successfully synthesized. X-ray diffraction analysis indicates that all the samples are single phased. The luminescence property is investigated in detail by measuring their photoluminescence excitation and emission spectra. Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors show strong absorption in 400–410 nm region, which is suitable for application in LEDs. When excited at 403 nm, Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphor can emit red emission with CIE chromaticity coordinates (0.615, 0.384). The optimal doping concentration of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} is measured to be 0.02. The thermal quenching property is also measured and compared with the commercial red phosphor Y{sub 2}O{sub 3}:Eu{sup 3+} (Topstar, TXC-RIA). The results indicate Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors have potential to serve as a red phosphor for white LEDs.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Luminescence properties of ZrW{sub 2}O{sub 8}:Eu{sup 3+} nanophosphors for white light emitting diodes

Highlights: • Eu{sup 3+} ions occupy C{sub 1} point group of the Zr{sup 4+} site in ZrW{sub 2}O{sub 8} crystals. • The optimum doping concentration of Eu{sup 3+} was determined for the red emission. • ZrW{sub 2}O{sub 8}:Eu possess high quantum efficiency and suitable chromaticity coordinates. - Abstract: ZrW{sub 2}O{sub 8}:Eu{sup 3+} nanophosphors (ca. 60 nm) with different Eu{sup 3+} doping concentrations were obtained using hydrothermal syntheses. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence excitation and emission spectra as well as decay curve measurements were used for the characterization. Under 466 nm excitation, strong red emission at 616 nm corresponding to {sup 5}D{sub 0}–{sup 7}F{sub 2} transition of Eu{sup 3+} was observed for ZrW{sub 2}O{sub 8}:Eu{sup 3+} (9 mol%) phosphors. The values of intensity parameter Ω{sub 2} and Ω{sub 4} are 17.82 × 10{sup −20} cm{sup 2} and 1.092 × 10{sup −20} cm{sup 2}, respectively. The high quantum efficiency of 83.5% of the ZrW{sub 2}O{sub 8}:Eu{sup 3+} (9 mol%) suggests this material could be promising red phosphor for generating white light in phosphor-converted white light-emitting diodes (LED)

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2015

Optical property investigations of polystyrene capped Ca{sub 2}P{sub 2}O{sub 7}:Dy{sup 3+} persistent phosphor

Highlights: • Synthesis of polymer capped pyrophosphate phosphors by citrate gel method. • Radiative lifetime is calculated from parameters of Judd-Ofelt theory and ICP-AES. • Reaction mechanism is discussed leading to high photoluminescence efficiency. • PL emission spectrum reveals broad band emission suitable for solid state lighting. - Abstract: By virtue of enhanced photosensivity, good optical response and better thermal stability, organic–inorganic hybrid materials are contemplated as one of the alternatives for designing advanced optoelectronic devices and innovative photonic applications. A novel inorganic organic hybrid Ca{sub 2}P{sub 2}O{sub 7}:Dy{sup 3+} phosphor has been fabricated by Pechini method. The optical property of synthesized phosphor is successfully altered by the in corporation of polystyrene sulfonic acid as capping agent in the colloidal solution. The phase purity and the average particle size of the prepared phosphor were calculated from X-ray diffraction (XRD) employing Debye Scherrer method. The morphological and chemical investigations were carried out through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. The radiative transitions are explained on the basis of Judd-Ofelt theory and on the basis of derived parameters, the radiative lifetime of persistent hybrid Ca{sub 2}P{sub 2}O{sub 7}:Dy{sup 3+} phosphor is calculated as 5.33 ms. This paper explores the mechanism leading to high photoluminescence efficiency using organic capping additives. The photoluminescence (PL) graphs reveal broad band emission at 482 nm (blue) and 573 nm (yellow) corresponding to {sup 4}F{sub 9/2}-{sup 6}H{sub 15/2} and {sup 4}F{sub 9/2}-{sup 6}H{sub 13/2} transitions of Dy{sup 3+}, respectively. The Commission International De I-Eclairage (CIE) chromaticity co-ordinates were calculated from emission spectra and the values (x, y) were approaching to standard value of white emission. The synthesized pyrophosphate phosphors can thereby account in multiple potential applications including white light emitting diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

White light emission and effect of annealing on the Ho{sup 3+}–Yb{sup 3+} codoped BaCa{sub 2}Al{sub 8}O{sub 15} phosphor

Graphical abstract: The upconversion emission spectra of the Ho{sup 3+}/Yb{sup 3+} doped/codoped BaCa{sub 2}Al{sub 8}O{sub 15} phosphors with different doping concentrations of Ho{sup 3+}/Yb{sup 3+} ions along with UC emission spectrum of the white light emitting phosphor annealed at 800 °C. - Highlights: • BaCa{sub 2}Al{sub 8}O{sub 15} phosphors codoped with Ho{sup 3+}–Yb{sup 3+} have been prepared by combustion method. • Phosphor annealed at 800 °C, illuminate an intense white light upon NIR excitation. • The sample annealed at higher temperatures emits in the pure green region. • The colour emitted persists in the white region even at high pump power density. • Developed phosphor is suitable for making upconverters and WLEDs. - Abstract: The BaCa{sub 2}Al{sub 8}O{sub 15} (BCAO) phosphors codoped with suitable Ho{sup 3+}–Yb{sup 3+} dopant concentration prepared by combustion method illuminate an intense white light upon near infrared diode laser excitation. The structural analysis of the phosphors and the detection of impurity contents have been performed by using the X-Ray Diffraction, FESEM and FTIR analysis. The purity of white light emitted from the sample has been confirmed by the CIE chromaticity diagram. Also, the white light emitted from the sample persists with the variation of pump power density. The phosphors emit upconversion (UC) emission bands in the blue, green and red region (three primary colours required for white light emission) along with one more band in the near infrared region of the electromagnetic spectrum. On annealing the white light emitting sample at higher temperatures, the sample starts to emit green colour and also the intensity of green and red UC emission bands get enhanced largely.

36 MATERIALS SCIENCE↗

DOE OSTI2015

A novel blue luminescent material Sr{sub 6}Ca{sub 4}(PO{sub 4}){sub 6}F{sub 2}:Eu{sup 2+}

Graphical abstract: - Highlights: • Novel Eu{sup 2+} doped Sr{sub 6}Ca{sub 4}(PO{sub 4}){sub 6}F{sub 2} phosphors was synthesized for the first time. • The Sr{sub 6}Ca{sub 4}(PO{sub 4}){sub 6}F{sub 2}:Eu{sup 2+} phosphors produced blue light when irradiated at 368 nm. • The emission band of the sample could be decomposed into two Gaussian profiles. - Abstract: For the first time, a series of novel blue light-emitting phosphors Sr{sub 6}Ca{sub 4}(PO{sub 4}){sub 6}F{sub 2}:Eu{sup 2+} were synthesized by a traditional solid-state reaction. The phosphors exhibited a broad and intense excitation band that could be pumped by near ultraviolet to exhibit a broad photoluminescence band ranging from 400 nm to 530 nm peaking at 452 nm. Quenching concentration was 0.05 mol. Furthermore, the mechanism of concentration quenching involving SCPF:Eu{sup 2+} was demonstrated to be a dipole–dipole interaction with critical distance of 27.95 Å. Decay time curves were also measured to validate energy transfer, and quantum efficiency is investigated. The chromaticity diagram of Commission Internationale de l’Eclairage indicated that SCPF:Eu{sup 2+} may be used as a blue-emitting component for white light-emitting diode applications.

36 MATERIALS SCIENCE↗

DOE OSTI2016

A novel single-phase white phosphor NaBaBO{sub 3}:Dy{sup 3+},K{sup +} for near-UV white light-emitting diodes

Highlights: • A white phosphor NaBaBO{sub 3}:Dy{sup 3+},K{sup +} with CIE coordinate (0.301, 0.308) was synthesized. • The optimum doping concentration of Dy{sup 3+} ions was found. • The effect and mechanism of K{sup +} ion as a charge compensator were discussed. • Temperature-dependent PL property of NaBaBO{sub 3}:Dy{sup 3+},K{sup +} was studied. • PL decay and quantum efficiency behaviors of the samples were investigated. - Abstract: A novel Dy{sup 3+}-doped NaBaBO{sub 3} white-emitting phosphor has been prepared by high temperature solid-state reaction method. The phase structure and luminescence properties of NaBaBO{sub 3}:Dy{sup 3+},K{sup +} samples were investigated. Photoluminescence results show that the as-prepared samples could be effectively excited by near-ultraviolet (NUV) light and generate white light emission due to the {sup 4}F{sub 9/2} → {sup 6}H{sub 15/2} (blue) transition and {sup 4}F{sub 9/2} → {sup 6}H{sub 13/2} (yellow) transition of Dy{sup 3+} ions, respectively. The optimum doping concentration of Dy{sup 3+} ions in the NaBaBO{sub 3} host was determined to be 5.0 mol% and the CIE chromaticity of the sample was determined to be (0.301, 0.308). Moreover, the mechanism of K{sup +} ion as a charge compensator on the improvement of photoluminescence property and the effect of temperature on the photoluminescence property of NaBaBO{sub 3}:Dy{sup 3+},K{sup +} were investigated. Furthermore, photoluminescence decay and quantum efficiency behaviors of NaBaBO{sub 3}:Dy{sup 3+},K{sup +} were also studied. The present work demonstrates that the NaBaBO{sub 3}:Dy{sup 3+},K{sup +} phosphor is a potential candidate for NUV white light emitting diodes.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Enhanced red emission induced by Tb{sup 3+} doping in europium-based molybdate phosphors

Graphical abstract: The introduction of Tb3+ significantly enhances the red emission of Eu3+ in europium-based molybdate phosphors. The enhanced red emission intensity is discussed by the relaxation of parity-forbidden selection rules of Eu3+ ions, whereas the contribution of Tb3+ → Eu3+ energy transfer is little in our case. - Highlights: • The introduction of Tb{sup 3+} significantly enhances the red emission of Eu{sup 3+} in europium-based molybdate phosphors. • At x = 0.02, the red-emitting intensity of LiEuMo{sub 2}O{sub 8} is enhanced by 30% under excitation at ultraviolet light 395 nm. • The enhanced red emission intensity is discussed by the relaxation of parity-forbidden selection rules of Eu{sup 3+} ions, whereas the contribution of Tb{sup 3+} → Eu{sup 3+} energy transfer is little in our case. - Abstract: A series of Tb{sup 3+}-doped europium-based molybdate red-emitting phosphors (LiEuMo{sub 2}O{sub 8}) were prepared by solid-state reaction method, their crystal structure and luminescence properties have been investigated by X-ray diffraction, micro-Raman spectra, diffuse reflectance spectra, photoluminescence and photoluminescence excitation spectra. Partial substitution of Li{sup +} by Tb{sup 3+} slightly distorts the host lattice, red-shifts the absorption edge of host and improves Eu{sup 3+} red-emitting intensity in LiEuMo{sub 2}O{sub 8} compound. The red-emitting intensity of LiEuMo{sub 2}O{sub 8} powder is enhanced by 30% at the doping level of 0.02 under excitation at 395 nm. In present study, we found that the contribution of Tb{sup 3+} → Eu{sup 3+} energy transfer to the enhanced Eu{sup 3+} emission is little since the Tb{sup 3+} ions are not responsive to the near ultraviolet (∼395 nm), the enhanced red emission is tentatively ascribed to the relaxation of parity-forbidden selection rules of Eu{sup 3+} ions. White light-emitting diodes are fabricated by using near ultraviolet light-emitting diode chips (∼395 nm) and the blends of the commercial blue, green and as-prepared red Li{sub 0.98}Tb{sub 0.02}EuMo{sub 2}O{sub 8} phosphor, the resulting white light-emitting diode shows a color-rendering index of 93.5, luminous efficacy of 14 lm/W and chromaticity coordinates of (0.292, 0.329).

36 MATERIALS SCIENCE↗

DOE OSTI2017

Citrate-based sol-gel synthesis of blue- and green-emitting BaLa{sub 2}WO{sub 7}:Tm{sup 3+} or Er{sup 3+} phosphors and their luminescence properties

Highlights: • The BLWO:Tm{sup 3+} or Er{sup 3+} phosphors were prepared by a citrate-based sol-gel method. • The BLWO:Tm{sup 3+} or Er{sup 3+} phosphors exhibited blue and green emissions under UV or NUV excitations. • The blue- and green-emitting BLWO:Tm{sup 3+} or Er{sup 3+} phosphors exhibited good thermal properties. - Abstract: BaLa{sub 2}WO{sub 7}:Tm{sup 3+} or Er{sup 3+} (BLWO:Tm{sup 3+} or Er{sup 3+}) single doped phosphors were prepared by a citrate-based sol-gel method. The crystalline properties of the prepared blue- and green-emitting phosphor materials were analyzed by X-ray diffraction (XRD) after annealing at 1350 °C. The XRD patterns of the both phosphors revealed monoclinic structure with a space group of P21/b. The morphological properties and elemental mappings of the BLWO:0.02Tm{sup 3+} and BLWO:0.01Er{sup 3+} phosphors were measured by field-emission scanning electron microscope images and energy dispersive X-ray spectrum, respectively. The photoluminescence (PL) spectra of BLWO:Tm{sup 3+} phosphors showed characteristic emission peaks of Tm{sup 3+} ions from the visible blue to near-infrared regions with the dominant emission at 799 nm ({sup 3}H{sub 4} → {sup 3}H{sub 6}) under ultraviolet (UV) and near-UV excitation wavelengths. Similarly, Er{sup 3+} ions activated BLWO phosphors exhibited intense green emissions at 548 nm ({sup 4}S{sub 3/2} → {sup 4}I{sub 15/2}) under the characteristic excitation wavelength of 381 nm. Furthermore, the temperature-dependent PL emission spectra and the luminescence decay curves were measured for the optimized BLWO:0.02Tm{sup 3+} and BLWO:0.01Er{sup 3+} phosphors. The chromaticity coordinates for the optimized blue- and green-emitting phosphors were calculated.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Low temperature synthesized SrMoO4:Eu3+ nanophosphors functionalized with ethylene glycol: A comparative study of synthesize route, morphology, luminescence and annealing

Highlights: • Tetragonal SrMoO{sub 4}:Eu{sup 3+} downconverting phosphors functionalized with ethylene glycol have been synthesized via three different preparation techniques (urea hydrolysis, ammonia hydrolysis and hydrothermal methods). • For the first time, a comparative study of synthesized route, morphology, luminescence and annealing has been given in detail. • Mechanism involved in the luminescence has been discussed with the help of schematic representation, energy level diagram and chromaticity diagram. • The prepared phosphors are suitable for biological labeling due to their dispersible capacity in different liquids (ethanol, phosphate buffered saline and water). - Abstract: Tetragonal SrMoO{sub 4}:Eu{sup 3+} downconverting phosphors functionalized with ethylene glycol have been synthesized via three different preparation techniques (urea hydrolysis, ammonia hydrolysis and hydrothermal methods). The developed phosphor shows strong red photoluminescence emission via electric dipole {sup 5}D{sub 0} → {sup 7}F{sub 2} transition and other weak transitions ({sup 5}D{sub 1} → {sup 7}F{sub 1}, {sup 5}D{sub 0} → {sup 7}F{sub 1}, {sup 5}D{sub 0} → {sup 7}F{sub 3} and {sup 5}D{sub 0} → {sup 7}F{sub 4}) by using three excitation wavelengths of 260, 395 and 464 nm. For the first time, a comprehensive discussion have been given for indirect and direct excitation for as-prepared phosphor prepared by the three different techniques. The needle imbedded spherical particles, elliptical shaped particles and orange carpels shaped particles have been obtained from the urea, ammonia and hydrothermal methods, respectively. The calculated quantum yields are found to be 7.5, 6.1 and 9.3% for urea, ammonia and hydrothermal based synthesized phosphors, respectively. The prepared phosphors are suitable for biological labeling due to their dispersible ability in different liquids (ethanol, phosphate buffered saline and water).

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Simple coating synthesis and enhanced luminescence behaviour of LiLa(MoO4)2:Eu3+@NaF

Highlights: • LiLa(MoO{sub 4}){sub 2}:Eu{sup 3+}{sub 0.06} @ (NaF){sub y wt} were synthesized with a simple coating method. • PL intensity can be enhanced as high as 4.80 times by coating NaF. • Enhancement PL intensity is a major effect, and increasing R is a minor effect. • LiLa(MoO{sub 4}){sub 2}:Eu{sup 3+}{sub 0.06} @ (NaF){sub 0.025 wt} was a phosphor with high R values (R = 5.89). - Abstract: A series of LiLa(MoO{sub 4}){sub 2}:Eu{sup 3+}@ (NaF){sub y wt} were prepared with a simple coating method. XRD results confirm that NaF coating will cause the slight expand of the lattice volume for the sample. Strongly enhanced emission effect inducing by NaF coating is observed. The emission spectra (PL) intensity of the optimal sample, LiLa(MoO{sub 4}){sub 2}:Eu{sup 3+}{sub 0.06} @ (NaF){sub 0.025wt} is as high as 4.8 times of that of LiLa(MoO{sub 4}){sub 2}:Eu{sup 3+}{sub 0.06}. Furthermore, dual emission properties inducing by NaF coating are observed. Enhancement emission of Eu{sup 3+} is a major effect, and increasing R is a minor effect. The optimal coating content of NaF is 2.5 wt%, which the corresponding chromaticity coordinates excited at 465 nm is x = 0.6650, y = 0.3347, which is nearly as same as the NTSC (National Television Standard Committee) standard values for red (x = 0.67, y = 0.33). So, it is a potential red-emitting phosphor with high R values (R = 5.89) for blue light-based white LED.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗