Sr2ZnWO6:Eu3+,Bi3+,Li+: a potential white‐emitting phosphor for near‐ultraviolet white light‐emitting diodes

A series of Sr₂ZnWO₆ phosphors co‐doped with Eu³⁺, Bi³⁺ and Li⁺ were prepared using the Pechini method. The samples were tested using X‐ray diffraction and luminescence spectroscopy. The results show that the samples can be effectively excited by near‐ultraviolet (UV) and UV light. The introduction of Bi³⁺ and Li⁺ significantly enhances the fluorescence emission of Sr₂ZnWO₆:Eu³⁺ and changes the light emitted by the phosphors from bluish‐green to white. When excited at 371 nm, Sr_2–x–zZn_1–yWO₆:xEu³⁺,yBi³⁺,zLi⁺ (x = 0.05, y = 0.05, z = 0.05, 0.1 and 0.15) samples emit high‐performance white light. Intense red–orange emission is also observed when excited by UV light. The obtained phosphor is a potential white‐emitting phosphor that could meet the needs of excitation sources with near‐UV chips. In addition, this phosphor might have promising application as a red–orange emitting phosphor for white light‐emitting diodes based on UV light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence behavior of Li2Sr1‐3x/2EuxSiO4 red phosphors for LED applications

Red‐emitting Li₂Sr_1‐3x/2Eu_xSiO₄ 0≤x≤0.5) phosphors were synthesized at 900°C in air by a solid‐state reaction. The synthesized phosphors were characterized by X‐ray powder diffraction, photoluminescence (PL) excitation (PLE) and PL spectra. The results from the PLE spectra suggest that the strong 394 nm excitation peak associated with the ⁵L₆ state of Eu³⁺ ions is of significance for near ultraviolet pumped white light‐emitting diodes and solid‐state lighting. It is also noted that the position of the charge transfer state of Eu³⁺ ions shifts towards the higher energy side (blue shift) by increasing the content of Eu³⁺ ions. The predominant emissions of Eu³⁺ ions under 394 nm excitation are observed at 580, 593, 614, 656 and 708 nm, which are attributed to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4), respectively. The PL results reveal that the optimal content of the red‐emitting Li₂Sr_1‐3x/2Eu_xSiO₄ phosphors is x = 0.475. Simulation of the white light excited by 394 nm near ultraviolet light has also been carried out for its potential white light‐emitting diode applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Co‐precipitation synthesis and luminescence properties of K2TiF6:Mn4+ red phosphors for warm white light‐emitting diodes

K₂TiF₆:Mn⁴⁺ red phosphors with different Mn⁴⁺ doping concentrations were obtained using the co‐precipitation method. X‐Ray diffraction, scanning electron microscopy, Raman spectra, Fourier transform infrared spectroscopy, photoluminescence excitation and emission spectra and decay curves were used to characterize the properties of K₂TiF₆:Mn⁴⁺ phosphors. Under excitation at 470 nm, an intense red emission peak around 631 nm corresponding to the ²E_g–⁴A₂ transition of Mn⁴⁺ was observed for 2.48 mol% K₂TiF₆:Mn⁴⁺ phosphors and was used as the optimum doping concentration. The excellent luminescent properties of K₂TiF₆:Mn⁴⁺ suggest that this material might be a promising red phosphor for generating warm white light in phosphor‐converted white light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

White‐ and blue‐light‐emitting dysprosium(III) and terbium(III)‐doped gadolinium titanate phosphors

Here we report the synthesis and structural, morphological, and photoluminescence analysis of white‐ and blue‐light‐emitting Dy³⁺‐ and Tm³⁺‐doped Gd₂Ti₂O₇ nanophosphors. Single‐phase cubic Gd₂Ti₂O₇ nanopowders consist of compact, dense aggregates of nanoparticles with an average size of ~25 nm for Dy³⁺‐doped and ~50 nm for Tm³⁺‐doped samples. The photoluminescence results indicated that ultraviolet (UV) light excitation of the Dy³⁺‐doped sample resulted in direct generation of white light, while a dominant yellow emission was obtained under blue‐light excitation. Intense blue light was obtained for Tm³⁺‐doped Gd₂Ti₂O₇ under UV excitation suggesting that this material could be used as a blue phosphor.     

Tunable white light emission from single‐phased Li2SrSiO4:Dy3+ phosphors by co‐doping with Eu3+

A series of single‐phase full‐color emitting Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors were synthesized by solid‐state reaction and characterized by X‐ray diffraction and photoluminescence analyses. The samples showed emission peaks at 488 nm (blue), 572 nm (yellow), 592 nm (orange) and 617 nm (red) under 393 nm excitation. The photoluminescence excitation spectra, comprising the Eu–O charge transfer band and 4f–4f transition bands of Dy³⁺ and Eu³⁺, range from 200 to 500 nm. The Commission Internationale de I'Eclairage chromaticity coordinates for Li₂Sr_0.98−xSiO₄:0.02Dy³⁺,xEu³⁺ phosphors were simulated. By manipulating Eu³⁺ and Dy³⁺ concentrations, the color points of Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ were tuned from the greenish‐white region to white light and eventually to reddish‐white region, demonstrating that a tunable white light can be obtained by Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors. Li₂Sr_0.98−xSiO₄:0.02Dy³⁺, xEu³⁺ can serve as a white‐light‐emitting phosphor for phosphor‐converted light‐emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.     

Optical properties and energy transfer of Eu2+/Ce3+ co‐activated Na3Ca6(PO4)5 phosphor

Ce³⁺/Eu²⁺ co‐doped Na₃Ca₆(PO₄)₅ phosphors were prepared using a combustion‐assisted synthesis method. X‐Ray powder diffraction (XRD) analysis confirmed the formation of a Na₃Ca₆(PO₄)₅ crystal phase. Na₃Ca₆(PO₄)₅:Eu²⁺ phosphors have an efficient bluish‐green emission band that peaks at 489 nm, whereas Ce³⁺‐doped Na₃Ca₆(PO₄)₅ showed a bright emission band at 391 nm. Analysis of the experimental results suggests that enhancement of the Eu²⁺ emission intensity in co‐doped Na₃Ca₆(PO₄)₅:Eu²⁺,Ce³⁺ phosphors is due to a resonance‐type energy transfer from Ce³⁺ to Eu²⁺ ions, which is predominantly governed by an exchange interaction mechanism. These results indicate that Ce³⁺/Eu²⁺ co‐doped Na₃Ca₆(PO₄)₅ is potentially useful as a highly efficient, bluish‐green emitting, UV‐convertible phosphor for white‐light‐emitting diodes. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence properties of red‐emission Mg4Nb2O9:Eu3+ phosphor

Red‐emitting Mg₄Nb₂O₉:Eu³⁺ phosphor is synthesized via a solid‐state reaction method in air, and its crystal structure and luminescence are investigated. The phosphor can be excited efficiently by ~ 395 nm light, coupled well with a ~ 395 nm near‐ultraviolet chip and emits red light at ~ 613 nm with sharp spectra due to ⁵D₀ → ⁷ F₂ transition of the Eu³⁺ ion. Mg₄Nb₂O₉:Eu³⁺ phosphor sintered at 1350 ºC shows Commission international de I'Eclairage (CIE) chromaticity coordinates of x = 0.6354, y = 0.3592, and is a potential red‐emitting phosphor candidate for white light‐emitting diodes (W‐LEDs) under ~ 395 nm near‐ultraviolet LED chip excitation. Copyright © 2014 John Wiley & Sons, Ltd.     

Eu3+‐activated Y2MoO6: a narrow band red‐emitting phosphor with strong near‐UV absorption

Near‐UV excited narrow line red‐emitting phosphors, Eu³⁺‐activated Y₂MoO₆ systems, were synthesized using a simple molten salt reaction. The structure and photoluminescence characteristics were investigated using X‐ray powder diffraction, UV–Vis absorption and fluorescent spectrophotometry. The excitation spectra show strong broad‐band absorptions in the near‐UV to blue light regions which match the radiation of near‐UV light‐emitting diode chips well. Under excitation of either near‐UV or blue light, intense red emission with a main peak of 611 nm is observed, ascribed to the ⁵D₀–⁷F₂ transition of Eu³⁺ ions; the optimal doping concentration is 20 mol%. The chromaticity coordinates (x = 0.65, y = 0.34) of the as‐obtained phosphor are very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that this material is a promising red‐emitting phosphor candidate for white‐LEDs based on near‐UV LED chips. Copyright © 2012 John Wiley & Sons, Ltd.     

Luminescence studies on Ba2ZnSi2O7 : Eu2+ phosphors crystals

A novel blue green‐emitting phosphor Ba₂ZnSi₂O₇ : Eu²⁺ was prepared by combustion synthesis method and an efficient bluish green emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 503 nm, which corresponds to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light‐emitting diodes (UV‐LEDs). The effect of doped Eu²⁺ concentration on the emission intensity of Ba₂ZnSi₂O₇ : Eu²⁺ was also investigated. The result indicates that Ba₂ZnSi₂O₇ : Eu²⁺ can be potentially useful as a UV radiation‐converting phosphor for white light‐emitting diodes. Copyright © 2009 John Wiley & Sons, Ltd.     

Tunable multicolor and white‐light upconversion luminescence in Yb3+/Tm3+/Ho3+ tri‐doped NaYF4 micro‐crystals

NaYF₄ micro‐crystals with various concentrations of Yb³⁺/Tm³⁺/Ho³⁺ were prepared successfully via a simple and reproducible hydrothermal route using EDTA as the chelating agent. Their phase structure and surface morphology were studied using powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns revealed that all the samples were pure hexagonal phase NaYF₄. SEM images showed that Yb³⁺/Tm³⁺/Ho³⁺ tri‐doped NaYF₄ were hexagonal micro‐prisms. Upconversion photoluminescence spectra of Yb³⁺/Tm³⁺/Ho³⁺ tri‐doped NaYF₄ micro‐crystals with various dopant concentrations under 980 nm excitation with a 665 mW pump power were studied. Tunable multicolor (purple, purplish blue, yellowish green, green) and white light were achieved by simply adjusting the Ho³⁺ concentration in 20%Yb³⁺/1%Tm³⁺/xHo³⁺ tri‐doped NaYF₄ micro‐crystals. Furthermore, white‐light emissions could be obtained using different pump powers in 20%Yb³⁺/1%Tm³⁺/1%Ho³⁺ tri‐doped NaYF₄ micro‐crystals at 980 nm excitation. The pump power‐dependent intensity relationship was studied and relevant energy transfer processes were discussed in detail. The results suggest that Yb³⁺/Tm³⁺/Ho³⁺ tri‐doped NaYF₄ micro‐crystals have potential applications in optoelectronic devices such as photovoltaic, plasma display panel and white‐light‐emitting diodes. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescent properties of single‐phase Ba2‐x‐1.5y‐1.5zP2O7:xEu2+,yCe3+, zTb3+ phosphors for white light‐emitting diode

A series of Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors was synthesized via a co‐precipitation method, then their crystal structure, quantum efficiency and luminescent properties were analyzed by XRD and FL, respectively. The results showed that these phosphors not only presented the excitation characteristics of Ba₂P₂O₇:xEu²⁺,zTb³⁺, but also exhibited that of the Ba₂P₂O₇:yCe³⁺,zTb³⁺ phosphor. Meanwhile, the tri‐doped phosphor showed a stronger absorption around 320 nm in contrast with the Eu²⁺/Ce³⁺:Tb³⁺ co‐doped phosphor. Not only can energy transfer from Ce³⁺→Eu²⁺ be observed; the energy transfer mechanism from Eu²⁺ to Tb³⁺ is discussed in the tri‐doped system. Ce³⁺ affects the luminescence properties of Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors just as the sensitizer whereas Eu²⁺ is considered both as the sensitizer and the activator. The chromaticity coordinates of tri‐doped phosphors excited at 320 nm stayed steadily in the bluish‐white light region,and the emitted color and color temperature (CCT) of these phosphors could be tuned by adjusting the relative contents of Eu²⁺, Ce³⁺ and Tb³⁺. Hence, the single phase Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors may be considered as potential candidates for white light‐emitting diodes.     

Enhanced luminescence and white light emission from Eu3+‐co‐doped K3Ca2(SO4)3Cl:Dy3+ phosphor with near visible ultraviolet excitation for white LEDs

The luminescent properties of europium (Eu)‐ and dysprosium (Dy)‐co‐doped K₃Ca₂(SO₄)₃Cl halosulfate phosphors were analyzed. This paper reports the photoluminescence (PL) properties of K₃Ca₂(SO₄)₃Cl microphosphor doped with Eu and Dy and synthesized using a cost‐effective wet chemical method. The phosphors were characterized by X‐ray diffraction and scanning electron microscopy. The CIE coordinates were calculated to display the color of the phosphor. PL emission of the prepared samples show peaks at 484 nm (blue), 575 nm (yellow), 594 nm (orange) and 617 nm (red). The emission color of the Eu,Dy‐co‐doped K₃Ca₂(SO₄)₃Cl halophosphor depends on the doping concentration and excitation wavelength. The addition of Eu in K₃Ca₂(SO₄)₃Cl:Dy greatly enhances the intensity of the blue and yellow peaks, which corresponds to the ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions (under 351 nm excitation). The Eu³⁺/Dy³⁺ co‐doping also produces white light emission for 1 mol% of Eu³⁺, 1 mol% of Dy³⁺ in the K₃Ca₂(SO₄)₃Cl lattice under 396 nm excitation, for which the calculated chromaticity coordinates are (0.35, 0.31). Thus, K₃Ca₂(SO₄)₃Cl co‐doped with Eu/Dy is a suitable candidate for NUV based white light‐emitting phosphors technology. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancement of the luminescence properties of Sr3(PO4)2:Dy3+,Li+ white‐light‐emitting phosphors by charge compensator Li+ co‐doping

Sr₃(PO₄)₂:Dy³⁺,Li⁺ phosphors were prepared using a simple high temperature solid method for luminescence enhancement. The structures of the as‐prepared samples agreed well with the standard phase of Sr₃(PO₄)₂, even when Dy³⁺ and Li⁺ were introduced. Under ultraviolet excitation at 350 nm, the Sr₃(PO₄)₂:Dy³⁺ sample exhibited two emission peaks at 483 nm and 580 nm, which were due to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, respectively. A white light was fabricated using these two emissions from the Sr₃(PO₄)₂:Dy³⁺ phosphors. The luminescence properties of Sr₃(PO₄)₂:Dy³⁺,Li⁺ phosphors, including emission intensity and decay time, were improved remarkably with the addition of Li⁺ as the charge compensator, which would promote their application in near‐ultraviolet excited white‐light‐emitting diodes.     

Photoluminescence in K3Ca2(SO4)3Cl‐doped Eu3+ phosphor

In this article we report Eu³⁺ luminescence in novel K₃Ca₂(SO₄)₃Cl phosphors prepared by wet chemical methods. The Eu³⁺ emission was observed at 594 nm and 615 nm, keeping the excitation wavelength constant at 396 nm nearer to light‐emitting diode excitation, Furthermore, phosphors were characterized by X‐ray diffraction for the confirmation of crystallinity. The variation of the photoluminescence intensity with impurity concentration has also been discussed. Thus, prominent emission in the red region makes prepared phosphors more applicable for white light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence characteristics of Sm3+‐doped Bi4Si3O12 red‐emitting phosphor

A series of novel red‐emitting Sm³⁺‐doped bismuth silicate phosphors, Bi₄Si₃O₁₂:xSm³⁺ (0.01 ≤ x ≤ 0.06), were prepared via the sol–gel route. The phase of the synthesized samples calcinated at 800 °C is isostructural with Bi₄Si₃O₁₂ according to X‐ray diffraction results. Under excitation with 405 nm light, some typical peaks of Sm³⁺ ions centered at 566, 609, 655 and 715 nm are found in the emission spectra of the Sm³⁺‐doped Bi₄Si₃O₁₂ phosphors. The strongest peak located at 609 nm is due to ⁴G_5/2–⁶H_7/2 transition of Sm³⁺. The luminescence intensity reaches its maximum value when the Sm³⁺ ion content is 4 mol%. The results suggest that Bi₄Si₃O₁₂:Sm³⁺ may be a potential red phosphor for white light‐emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.     

Luminescent properties of Ca3SiO4Cl2 co‐doped with Ce3+ and Eu2+ for near‐ultraviolet light‐emitting diodes

Ca₃SiO₄Cl₂ co‐doped with Ce³⁺,Eu²⁺ was prepared by high temperature reaction. The structure, luminescent properties and the energy transfer process of Ca₃SiO₄Cl₂: Ce³⁺,Eu²⁺ were investigated. Eu²⁺ ions can give enhanced green emission through Ce³⁺ → Eu²⁺ energy transfer in these phosphors. The green phosphor Ca_2.9775SiO₄Cl₂:0.0045Ce³⁺,0.018Eu²⁺ showed intense green emission with broader excitation in the near‐ultraviolet light range. A green light‐emitting diode (LED) based on this phosphor was made, and bright green light from this green LED could be observed by the naked eye under 20 mA current excitation. Hence it is considered to be a good candidate for the green component of a three‐band white LED. Copyright © 2015 John Wiley & Sons, Ltd.     

Zn‐doped CaTiO3:Eu3+ red phosphors for enhanced photoluminescence in white LEDs by solid‐state reaction

Zn‐doped CaTiO₃:Eu³⁺ red phosphors for enhanced photoluminescence in white light‐emitting diodes (LEDs) were synthesized by a solid‐state method. The structure and morphology of the obtained phosphor samples were observed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), and the impact of Ca, Zn and Eu content on their photoluminescence properties was studied. The results indicated that Zn not only participates in the formation of defects in suitable lattice matrices but also has a role in flux in the transformation from ZnO to Zn₂TiO₄, which is beneficial for the enhancement of photoluminescence properties. Photoluminescence test data showed that the Zn‐doped phosphor is excited efficiently by near‐ultraviolet (NUV) light at wavelengths around 398 nm and emits an intense red light with a broad peak around 616 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺. The intensity of this phosphor emission is three times stronger than that without Zn‐doping. Furthermore, this phosphor has very good thermal stability, high color purity and a low sintered temperature, all of which suggest its potential as a promising red phosphor for white LEDs. Copyright © 2015 John Wiley & Sons, Ltd.     

Size‐tailored synthesis and luminescent properties of three‐dimensional BaMoO4, BaMoO4:Eu3+ micron‐octahedrons and micron‐flowers via sonochemical route

Almost monodisperse three‐dimensional (3D) BaMoO_4, BaMoO₄:Eu³⁺ micron‐octahedrons and micron‐flowers were successfully prepared via a large‐scale and facile sonochemical route without using any catalysts or templates. X‐Ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy dispersion X‐ray (EDS), Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopy were employed to characterize the as‐obtained products. It was found that size modulation could be easily realized by changing the concentrations of reactants and the pH value of precursors. The formation mechanism for micron‐octahedrons and micron‐flowers was proposed on the basis of time‐dependent experiments. Using excitation wavelengths of 396 or 466 nm for BaMoO₄:Eu³⁺ phosphors, an intense emission line at 614 nm was observed. These phosphors might be promising components with possible application in the fields of near UV‐ and blue‐excited white light‐emitting diodes. Simultaneously, this novel and efficient pathway could open new opportunities for further investigating the properties of molybdate materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluorescence enhancement of europium (III) perchlorate by 1,10‐phenanthroline on the 1‐(naphthalen‐2‐yl)‐2‐(phenylsulthio)ethanone complex and luminescence mechanism

A novel ligand, 1‐(naphthalen‐2‐yl)‐2‐(phenylsulthio)ethanone was synthesized using a new method and its two europium (Eu) (III) complexes were synthesized. The compounds were characterized by elemental analysis, coordination titration analysis, molar conductivity, infrared, thermo gravimetric analyzer‐differential scanning calorimetry (TGA‐DSC), ¹H NMR and UV spectra. The composition was suggested as EuL₅ · (ClO₄)₃ · 2H₂O and EuL₄ · phen(ClO₄)₃ · 2H₂O (L = C₁₀H₇COCH₂SOC₆H₅). The fluorescence spectra showed that the Eu(III) displayed strong characteristic metal‐centered fluorescence in the solid state. The ternary rare earth complex showed stronger fluorescence intensity than the binary rare earth complex in such material. The strongest characteristic fluorescence emission intensity of the ternary system was 1.49 times as strong as that of the binary system. The phosphorescence spectra were also discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

1T′‐ReS2 Confined in 2D‐Honeycombed Carbon Nanosheets as New Anode Materials for High‐Performance Sodium‐Ion Batteries

ReS₂ (rhenium disulfide) is a new transition‐metal dichalcogenide that exhibits 1T′ phase and extremely weak interlayer van der Waals interactions. This makes it promising as an anode material for sodium‐ion batteries. However, achieving both a high‐rate capability and a long‐life has remained a major research challenge. Here, a new composite is reported, in which both are realized for the first time. 1T′‐ReS₂ is confined through strong interfacial interaction in a 2D‐honeycombed carbon nanosheets that comprise an rGO inter‐layer and a N‐doped carbon coating‐layer (rGO@ReS₂@N‐C). The strong interfacial interaction between carbon and ReS₂ increases overall conductivity and decreases Na⁺ diffusion resistance, whilst the intended 2D‐honeycombed carbon protective layer maintains structural morphology and electrochemical activity during long‐term cycling. These findings are confirmed by advanced characterization techniques, electrochemical measurement, and density functional theory calculation. The new rGO@ReS₂@N‐C exhibits the greatest rate performance reported so far for ReS₂ of 231 mAh g^?1 at 10 A g^?1. Significantly, this is together with ultra‐stable long‐term cycling of 192 mAh g^?1 at 2 A g^?1 after 4000 cycles.