Solid‐state synthesis and luminescent properties of yellow‐emitting phosphor NaY(MoO4)2:Dy3+ for white light‐emitting diodes

A yellow‐emitting phosphor NaY(MoO₄)₂:Dy³⁺ was synthesized using a solid‐state reaction at 550 °C for 4 h, and its luminescent properties were investigated. Its phase formation was studied using X‐ray powder diffraction analysis, and there were no crystalline phases other than NaY(MoO₄)₂. NaY(MoO₄)₂:Dy³⁺ produced yellow emission under 386 or 453 nm excitation, and the prominent luminescence was yellow (575 nm) due to the ⁴ F_9/2→⁶H_13/2 transition of Dy³⁺. For the 575 nm emission, the excitation spectrum had one broad band and some narrow peaks; the peaks were located at 290, 351, 365, 386, 426, 453 and 474 nm. Emission intensities were influenced by the Dy³⁺ doping content and a concentration quenching effect was observed; the phenomenon was also proved by the decay curves. Moreover, the Commission International de I'Eclairage chromaticity coordinates of NaY(MoO₄)₂:Dy³⁺ showed similar values at different Dy³⁺ concentrations, and were located in the yellow region. Copyright © 2015 John Wiley & Sons, Ltd.     

Insights into the discrepant luminescence for BaSiO3:Eu2+ phosphors prepared by solid‐state reaction and precipitation reaction methods

Two synthesis routes, solid‐state reaction and precipitation reaction, were employed to prepare BaSiO₃:Eu²⁺ phosphors in this study. Discrepancies in the luminescence green emission at 505 nm for the solid‐state reaction method sample and in the yellow emission at 570 nm for the sample prepared by the precipitation reaction method, were observed respectively. A detail investigation about the discrepant luminescence of BaSiO₃:Eu²⁺ phosphors was performed by evaluation of X‐ray diffraction (XRD), photoluminescence (PL)/photoluminescence excitation (PLE), decay time and thermal quenching properties. The results showed that the yellow emission was generated from the BaSiO₃:Eu²⁺ phosphor, while the green emission was ascribed to a small amount of Ba₂SiO₄:Eu²⁺ compound that was present in the solid‐state reaction sample. This work clarifies the luminescence properties of Eu²⁺ ions in BaSiO₃ and Ba₂SiO₄ hosts.     

Photoluminescence properties of a novel phosphor CaB2O4:Eu3+ under NUV excitation

The new borate phosphor CaB₂O₄:Eu³⁺ was synthesized by solid‐state method and their photoluminescence properties were investigated. The results show that the pure phase of CaB₂O₄ could be available at 900°C, CaB₂O₄:Eu³⁺ phosphor could be effectively excited by the near ultraviolet light (NUV) (392 nm), and the luminescent intensity of CaB₂O₄:Eu³⁺ phosphor reached to the highest when the doped‐Eu³⁺ content was 4 mol%. The emission spectra of CaB₂O₄:Eu³⁺ phosphor could exhibit red emission at 612 nm and orange emission at 588 nm, which are ascribed to the ⁵D₀–⁷F₂ and ⁵D₀–⁷F₁ transitions of Eu³⁺ ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermoluminescence characterization of Dy3+‐activated Mg5(BO3)3F low Zeff phosphor

Thermoluminescence characteristics of Dy³⁺‐activated Mg₅(BO₃)₃F low Z_eff phosphor are described. The Mg₅(BO₃)₃F phosphor doped with Dy³⁺ as activator was prepared by the modified solid‐state reaction. Formation of the compound was confirmed by use of X‐ray powder diffraction. The X‐ray powder diffraction pattern of the as‐prepared compound shows a good match with the available JCPDS data. The γ‐irradiated Mg₅(BO₃)₃F:Dy³⁺ phosphor shows a simple glow curve peaking at about 148°C indicating that only one type of trap is being activated within a particular temperature range. The kinetic parameters, including activation energy and frequency factor were determined using Chen's method. The activation energy and frequency factors were 0.75 eV and 4.508 × 10⁹/s respectively. The Z_eff of Mg₅(BO₃)₃F:Dy³⁺ phosphor was 9.84. Copyright © 2012 John Wiley & Sons, Ltd.     

Ca3(PO4)2:Eu3+ phosphor preparation with different morphologies and their fluorescence properties

Ca₃(PO₄)₂:Eu³⁺ phosphor was prepared using a facile chemistry method in the presence of surfactants. The effects of surfactants on the morphology and photoluminescence properties of Ca₃(PO₄)₂:Eu³⁺ phosphor were investigated. The morphology of the phosphor was significantly influenced by the surfactants employed. When nonionic surfactant glyceryl monostearate and anionic surfactant sodium dodecylbenzene sulfonate were employed, the phospor powders are composed of a large number of homogeneous spherical particles with sizes of 0.3–0.6 µm and 2–3 µm, respectively. By contrast, when cationic surfactant cetyltrimethylammonium bromide was used, the morphology of the phosphor is completely different. The product is an excellent cuboid, and the phosphor prepared with 2.5 mmol cetyltrimethylammonium bromide showed higher luminescent intensity than phosphors prepared with the other two types of surfactants. Copyright © 2013 John Wiley & Sons, Ltd.     

Eu3+-activated red phosphor Ca3YAl3B4O15 with low thermal quenching behaviour

This paper reports a sequence of a Ca₃YAl₃B₄O₁₅:xEu³⁺ red phosphor prepared using a high-temperature solid-state reaction. At the excitation of 396 nm, the samples emitted intense red emission centred at ~623 nm, which could be attributed to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ion. The results showed that the optimum Eu³⁺ doping concentration of Ca₃YAl₃B₄O₁₅:Eu³⁺ phosphor was x = 80 mol%, and the concentration quenching mechanism of Ca₃YAl₃B₄O₁₅:Eu³⁺ red phosphor belonged to the exchange coupling between Eu³⁺ ions. The Commission Internationale de l'éclairage (CIE) coordinates and colour purity of Ca₃Y_0.2Al₃B₄O₁₅:0.8Eu³⁺ were calculated as (0.6375, 0.3476) and 95.5%, respectively. Moreover, the red emission of the obtained phosphor Ca₃YAl₃B₄O₁₅:0.8Eu³⁺ exhibited a low thermal quenching behaviour with an intensity retention rate of 92.85% at 150°C. The above results manifest that the Eu³⁺-activated Ca₃YAl₃B₄O₁₅ phosphor is predicted to be a promising red luminescent component for white light-emitting diodes.     

A novel red phosphor Ca2YNbO6:Eu3+ for WLEDs

Due to the advantages of good physicochemical properties, thermal stability, and optical properties, double perovskite compounds have received extensive attention. On this basis, a new type of red phosphor, Ca₂YNbO₆:xEu³⁺, was synthesized using a high-temperature solid-phase method. Its phase purity, morphology, elemental composition, absorption spectrum, photoluminescence, thermal stability, and Commission Internationale de l'éclairage (CIE) chromaticity coordinates were thoroughly investigated. The results display that there is no impurity phase in the samples and the convergence factor R_wp = 14.2%; the microscopic particles are uniform and full, and the distribution of each element is uniform. The energy band gap ΔE is between 3.71 eV and 3.65 eV. The luminescence intensity is the best when the doped Eu³⁺ concentration x reaches 0.4, and emits 612 nm red light (⁵D₀→⁷F₂) under 465 nm excitation, and the concentration quenching is attributed to a d–d interaction. The luminescence intensity at 425 K was still 75% of the room temperature luminescence intensity, which indicates that the thermal stability is extremely superior. The CIE chromaticity coordinates (0.6534, 0.3455) of the Ca2YNbO6:0.4Eu³⁺ phosphors are very close to National Television Standards Committee (0.670, 0.330), and the samples have low correlated colour temperature (2656 K) and high colour purity (99.90%). All findings suggest that Ca₂YNbO₆:Eu³⁺ can serve as a substitute for red phosphor in WLEDs.     

Combustion synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+, Tb3+ phosphor.

Eu(2+), Dy(3+) and Tb(3+) co-doped strontium aluminate phosphor with high brightness and long afterglow was synthesized by a combustion method, using urea as a reducer. The properties of SrAl(2)O(4):Eu(2+),Dy(3+),Tb(3+) phosphor with a series of initiating combustion temperatures, urea concentrations and boric acid molar fractions were investigated. The sample at initiating combustion temperature of 600 degrees C exhibited an intense emission peak at 513 nm, in which the phosphor existed as a single-phase monoclinic structure. The experimental results showed that the optimum ratio of urea is 2.0 times higher than theoretical quantities and that the suitable molar fraction of H(3)BO(3) is 0.08. The average particle size of the phosphor was 50-80 nm and its luminescence properties were studied systematically. Compared with SrAl(2)O(4):Eu(2+),Dy(3+) phosphor, the initial luminescence brightness improved from 2.50 candela (cd)/m(2) to 3.55 cd/m(2) and the long afterglow time was prolonged from 1290 s to 2743 s.     

Luminescence properties of green‐emitting Ca2MgSi2O7:Eu2+ phosphor by a solid‐state reaction method

A europium (Eu)‐doped di‐calcium magnesium di‐silicate phosphor, Ca₂MgSi₂O₇:Eu²⁺, was prepared using a solid‐state reaction method. The phase structure, particle size, surface morphology, elemental analysis, different stretching mode and luminescence properties were analyzed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) with energy dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and mechanoluminescence (ML). The phase structure of Ca₂MgSi₂O₇:Eu²⁺ was an akermanite‐type structure, which belongs to the tetragonal crystallography with space group P4?2₁m; this structure is a member of the melilite group and forms a layered compound. The surface of the prepared phosphor was not found to be uniform and particle distribution was in the nanometer range. EDX and FTIR confirm the components of Eu²⁺‐doped Ca₂MgSi₂O₇ phosphor. Under UV excitation, the main emission peak appeared at 530 nm, belonging to the broad emission ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The ML intensity of the prepared phosphor increased linearly with increasing impact velocity. A CIE color chromaticity diagram and ML spectrum confirmed that the prepared Ca₂MgSi₂O₇:Eu²⁺ phosphor would emit green color and the ML spectrum was similar to that of PL, which indicated that ML is emitted from the same center of Eu²⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence study of Eu3+doped Li6Y(BO3)3 phosphor for solid‐state lighting

In this study, Li₆Y_1–xEu_x(BO₃)₃ phosphor was successfully synthesized using a modified solid‐state diffusion method. The Eu³⁺ ion concentration was varied at 0.05, 0.1, 0.2, 0.5 and 1 mol%. The phosphor was characterized for phase purity, morphology, luminescent properties and molecular transmission at room temperature. The XRD pattern suggests a result closely matching the standard JCPDS file (#80‐0843). The emission and excitation spectra were followed to discover the luminescence traits. The excitation spectra indicate that the current phosphor can be efficiently excited at 395 nm and at 466 nm (blue light) to give emission at 595 and 614 nm due to the ⁵D₀ → ⁷F_j transition of Eu³⁺ ions. Concentration quenching was observed at 0.5 mol% Eu³⁺ in the Li₆Y_1–xEu_x(BO₃)₃ host lattice. Strong red emission with CIE chromaticity coordinates of phosphor is x = 0.63 and y = 0.36 achieved with dominant red emission at 614 nm the ⁵D₀ → ⁷ F₂ electric dipole transition of Eu³⁺ ions. The novel Li₆Y_1–xEu_x(BO₃)₃ phosphor may be a suitable red‐emitting component for solid‐state lighting using double‐excited wavelengths, i.e. near‐UV at 395 nm and blue light at 466 nm. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural characterization and optical properties of Ca2MgSi2O7:Eu2+,Dy3+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was prepared by the solid‐state reaction method under a weak reducing atmosphere. The obtained phosphor was characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared (FT‐IR) techniques. The phase structure of the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was akermanite type, which is a member of the melilite group. The surface morphology of the sintered phosphor was not uniform and phosphors aggregated tightly. EDX and FT‐IR spectra confirm the elements present in the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor. Under UV excitation, a broadband emission spectrum was found. The emission spectra observed in the green region centered at 535 nm, which is due to the 4f–5d transition. The mechanoluminescence (ML) intensity of the prepared phosphor increased linearly with increases in the mechanical load. The ML spectra were similar to the photoluminescence (PL), which indicates that ML is emitted from the same emitting center of Eu²⁺ ions as PL. Copyright © 2014 John Wiley & Sons, Ltd.     

Persistent luminescence of CaMgSi2O6:Eu2+,Dy3+ and CaMgSi2O6:Eu2+,Ce3+ phosphors prepared using the solid‐state reaction method

CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were synthesized using the solid‐state reaction method. X‐Ray diffraction (XRD) and photoluminescence (PL) analyses were used to characterize the phosphors. The XRD results revealed that the synthesized CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were crystalline and are assigned to the monoclinic structure with a space group C2/c. The calculated crystal sizes of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors with a main (221) diffraction peak were 44.87 and 53.51 nm, respectively. Energy‐dispersive X‐ray spectroscopy (EDX) confirmed the proper preparation of the sample. The PL emission spectra of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors have a broad band peak at 444.5 and 466 nm, respectively, which is due to electronic transition from 4f⁶5d¹ to 4f⁷. The afterglow results indicate that the CaMgSi₂O₆:Eu²⁺,Dy³⁺ phosphor has better persistence luminescence than the CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation,characterization and luminescence properties of BiPO4:Eu nanophosphors

A facile chemical method was employed to prepare fine BiPO₄:Eu³⁺ phosphor particles calcined at the same temperature. Introducing lithium greatly affected the morphology of the samples and further affected the luminescence intensity. The samples were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. The XRD patterns of BiPO₄:Eu³⁺ indicated a monoclinic phase. From the fluorescence spectra, the emission transition ⁵D₀ → ⁷F₁ is more prominent than the normal red emission transition ⁵D₀ → ⁷F₂. Based on the intensity ratios of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ in the emission spectra, it can be concluded that introducing Li⁺ can improve the symmetry of the crystal lattice and modify the emission intensity. Sharp lines at 395 nm are the strongest of the f–f transitions and match well with near‐UV LED chips. Copyright © 2012 John Wiley & Sons, Ltd.     

Microwave‐assisted sintering synthesis of greenish‐yellow emitting Sr2SiO4:Eu2+ phosphors

Europium ion (Eu²⁺) doped Sr₂SiO₄ phosphors with greenish‐yellow emission were synthesized using microwave‐assisted sintering. The phase structure and photoluminescence (PL) properties of the obtained phosphor samples were investigated. The PL excitation spectra of the Sr₂SiO₄:Eu²⁺ phosphors exhibited a broad band in the range of 260 nm to 485 nm with a maximum at 361 nm attributed to the 5f‐4d allowed transition of the Eu²⁺ ions. Under an excitation at 361 nm, the Sr₂SiO₄:Eu²⁺ phosphor exhibited a greenish‐yellow emission peak at 541 nm with an International‐Commission‐on‐Illumination (CIE) chromaticity of (0.3064, 0.4772). The results suggest that the microwave‐assisted sintering method is promising for the synthesis of phosphors owing to the decreased sintering time without the use of additional reductive agents.     

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.     

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.     

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.     

Luminescence enhancement of (Sr1–xMx)2SiO4:Eu2+ phosphors with M (Ca2+/Zn2+) partial substitution for white light‐emitting diodes

Eu²⁺‐doped Sr₂SiO₄ phosphor with Ca²⁺/Zn²⁺ substitution, (Sr_1–xM_x)₂SiO₄:Eu²⁺ (M = Ca, Zn), was prepared using a high‐temperature solid‐state reaction method. The structure and luminescence properties of Ca²⁺/Zn²⁺ partially substituted Sr₂SiO₄:Eu²⁺ phosphors were investigated in detail. With Ca²⁺ or Zn²⁺ added to the silicate host, the crystal phase could be transformed between the α‐form and the β‐form of the Sr₂SiO₄ structure. Under UV excitation at 367 nm, all samples exhibit a broad band emission from 420 to 680 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. The broad emission band consists of two peaks at 482 and 547 nm, which correspond to Eu²⁺ ions occupying the ten‐fold oxygen‐coordinated Sr.(I) site and the nine‐fold oxygen‐coordinated Sr.(II) site, respectively. The luminescence properties, including the intensity and lifetime of Sr₂SiO₄:Eu²⁺ phosphors, improved remarkably on Ca²⁺/Zn²⁺ addition, and promote its application in white light‐emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.     

Luminescent properties of novel red‐emitting M7Sn(PO4)6:Eu3+ (M = Sr,Ba) for light‐emitting diodes

Novel red‐emitting phosphors, Eu³⁺‐activated M₇Sn(PO₄)₆ (M = Sr, Ba), were synthesized at 1200°C by conventional solid‐state reaction method. The luminescent properties of M₇Sn(PO₄)₆:Eu³⁺ (M = Sr, Ba) phosphors were investigated, and the critical concentration of the activator (Eu³⁺) concentration were found to be 0.175 mol and 0.21 mol per formula unit for Sr_7‐xSn(PO₄)₆:xEu³⁺ and Ba_7‐xSn(PO₄)₆:xEu³⁺, respectively. These phosphors presented red luminescence under the excitation of 395 or 465 nm, perfectly matching with the emissions wavelength of near‐ultraviolet (UV) light‐emitting diodes (LEDs) and InGaN blue LED.     

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.