Optical characterization and the energy level scheme for Ce3+‐doped BaY2Si3O10 blue‐emitting phosphor

A series of Ce³⁺‐activated blue‐emitting phosphors BaY₂Si₃O₁₀ (BYSO) was designed and synthesized by a conventional solid‐state method. Upon ultraviolet light (250–370 nm) excitation, the obtained phosphors showed an intense blue emission band centered at 400–427 nm depending on doping concentration, and corresponding to the 5d→4f transition of Ce³⁺. The effects of doping concentration on crystal structure, emitting color, photoluminescence and photoluminescence excitation spectra, as well as the concentration quenching mechanism were studied in detail. The optimal doping concentration of Ce³⁺ in this phosphor was demonstrated to be about 0.75% and the concentration quenching mechanism can be ascribed to electric dipole–dipole interactions with a critical distance of ~38 Å. These fine luminescence properties indicate that BYSO:Ce³⁺ may be a potential blue phosphor for full‐color ultra‐violet (UV) white light emitting diodes (WLEDs).     

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.     

Cation‐tunable blue phosphor Ca2PO4Cl:Eu2+: enhancive emission and site occupancy

A series of blue phosphors Ca_1.98–xM_xPO₄Cl:0.02Eu²⁺ (M = Mg and Sr) with different values of x were synthesized using a high‐temperature solid‐state reaction. X‐Ray diffraction and photoluminescence measurements were used to study the phase structure and luminescence properties. Ca₂PO₄Cl:0.02Eu²⁺ exhibits a tunable emission intensity and color due to the incorporation of Sr²⁺ or Mg²⁺. The incorporation of Sr²⁺ reduces the luminescence intensity and results in a slight red shift in the emission band. The incorporation of Mg²⁺ results in enhanced emission and a clear blue shift in the emission band along with a tunable chromatic coordination. Under excitation at λ = 334 nm, the emission intensity of the Mg²⁺‐doped Ca₂PO₄Cl:0.02Eu²⁺ is found to be 250% that of Ca₂PO₄Cl:0.02Eu²⁺. The luminescence behaviors of the as‐synthesized phosphors are discussed according to the host crystal structure and site occupancy of Eu²⁺. The results indicate that Mg²⁺‐doped Ca₂PO₄Cl:Eu²⁺ is more applicable as a near‐UV‐convertible blue phosphor for white light‐emitting diodes. 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.     

Synthesis and luminescence characterization of Y2BaZnO5:RE (RE = Eu3+, Tb3+, Pr3+ and Sm3+) phosphors

Modified synthesis and luminescence of Y₂BaZnO₅ phosphors activated with the rare earths (RE) Eu³⁺, Tb³⁺, Pr³⁺ and Sm³⁺ are reported. RE₂BaZnO₅ phosphors have attracted attention because of their interesting magnetic and optical properties; and are usually prepared using a two‐step solid‐state reaction. In the first step, carbonates or similar precursors are thoroughly mixed and heated at 900°C to decompose them to oxides. To eliminate the unwanted phases like BaRE₂O₄, the resulting powders are reheated at 1100°C for a long time. We prepared Y₂BaZnO₅ phosphors activated with various activators by replacing the first step with combustion synthesis. The photoluminescence results are presented. The photoluminescence results for Eu³⁺, Tb³⁺ and Pr³⁺ are in good agreement with the literature. However, photoluminescence emission from Sm³⁺ has not been documented previously. The excitation spectrum of Eu³⁺ is dominated by a charge transfer band around 261 nm, and an additional band around 238 nm is always present, irrespective of the type of activator. The presence of this band for all these different types of activators was interpreted as host absorption.     

Sol‐gel synthesis and luminescent properties of red‐emitting Y(P,V)O4:Eu3+ phosphors

Eu³⁺‐activated Y(P,V)O₄ phosphors were prepared by the EDTA sol‐gel method, and the corresponding morphologies and luminescent properties were investigated. The sample particles were relatively spheroid with size of 2–3 µm and had a smooth surface. The excitation spectra for Y(P,V)O₄:Eu³⁺ consisted of three strong excitation bands in the 200–350 nm range, which were attributed to a Eu³⁺‐ O^2? charge‐transfer band and ¹A₁?¹ T₁/¹ T₂ transitions in VO₄^3?. The as‐synthesized phosphors exhibited a highly efficient red luminescence at 613 nm due to the Eu^{3+ 5}D₀?⁷ F₂ electric dipole transition. With the increase in the V⁵⁺/P⁵⁺ ratio, the luminescence intensity of the red phosphor under UV excitation was greatly improved due to enhanced VO₄^3? → Eu³⁺ energy transfer. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence of EuII in barium zinc orthosilicate: a novel green color emitting phosphor for white‐LEDs

A series of Eu²⁺‐activated barium orthosilicates (BaZnSiO₄) were synthesized using a high‐temperature solid‐state reaction. A photoluminescence excitation study of Eu²⁺ shows a broad absorption band in the range of 270–450 nm, with multiple absorption peak maxima (310, 350 and 400 nm) due to 4f–5d electronic transition. The emission spectra of all the compositions show green color emission (in the spectral region 450–550 nm with a peak maximum at 502 nm and a shoulder at ~ 490 nm) with appropriate Comission Internationale de l'Eclairage (CIE) color coordinates. The two emission peaks are due to the presence of Eu²⁺ in two different Ba sites in the BaZnSiO₄ host lattice. The energy transfers between the Eu²⁺ ions in BaZnSiO₄ host are elucidated from the critical concentration quenching data based on the electronic multipolar interaction. All Eu²⁺‐activated BaZnSiO₄ phosphor materials can be efficiently excited in the ultraviolet (UV) to near UV‐region (270–420 nm), making them attractive candidate as a green phosphor for solid state lighting–white light‐emitting diodes.     

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.     

Novel blue‐emitting SrMg2Al16O27:Eu2+ phosphor for solid‐state lighting

Eu²⁺‐activated SrMg₂Al₁₆O₂₇ novel phosphor was synthesized by a combustion method (550°C furnace). The prepared phosphor was first characterized by X‐ray diffraction (XRD) for confirmation of phase purity. SEM analysis showed the morphology of the phosphor. The photoluminescence characteristics showed broad‐band excitation at 324 nm, which was monitored at 465 nm emission wavelength. The SrMg₂Al₁₆O₂₇:Eu²⁺ phosphor shows broad blue emission centred at 465 nm, emitting a blue light corresponding to 4f⁶5d¹ → 4f⁷ transition. Here we report the photoluminescence characteristics of the prepared phosphor and compare it with commercial BAM:Eu²⁺ phosphor. Copyright © 2011 John Wiley & Sons, Ltd.     

Luminescent properties of MAl(SO4)2Br:Eu3+ (M = Sr or Mg) red phosphors for near‐UV light‐emitting diodes

Eu³⁺‐activated MAl(SO₄)₂Br phosphors (where M = Mg or Sr) are successfully prepared using a wet chemical reaction technique. The samples are characterized by X‐ray diffraction (XRD) and photoluminescence (PL) spectroscopies. The XRD pattern revealed that both the samples are microcrystalline in nature. PL of Eu³⁺‐doped SrAl(SO₄)₂Br and MgAl(SO₄)₂Br phosphors exhibited characteristic red emission coming from the ⁵D₀ → ⁷F₂ (616 nm) electron transition, when excited by 396 nm wavelength of light. The maximum intensity of luminescence was observed at a concentration of 1 mol% Eu³⁺. The intensity of the electric dipole transition at 616 nm is greater than that of the magnetic dipole transition at 594 nm. The results showed that MAl(SO₄)₂Br:Eu³⁺, (M = Mg, Sr) phosphors have potential application in near‐UV light‐emitting diodes as efficient red‐emitting phosphor. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal quenching of luminescence of LiSr4(BO3)3:Eu2+ orange‐emitting phosphor

An orange‐emitting phosphor, Eu²⁺‐activated LiSr₄(BO₃)₃, was synthesized using the conventional solid‐state reaction. The photoluminescence excitation and emission spectra, and temperature dependence of the luminescence intensity of the phosphor were investigated. The results showed that LiSr₄(BO₃)₃:Eu²⁺ could be efficiently excited by incident light of 250–450 nm, and emits a strong orange light. With increasing temperature, the emission bands of LiSr₄(BO₃)₃:Eu²⁺ show an abnormal blue‐shift with broadening bandwidth and decreasing emission intensity. Copyright © 2013 John Wiley & Sons, Ltd.     

Combustion synthesis of blue‐emitting submicron CaAl4O7:Eu2+, Dy3+ persistence phosphor

Long persistence phosphor CaAl₄O₇: Eu²⁺, Dy³⁺ were prepared by a combustion method. The phosphors were characterized by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), decay time measurement techniques and photoluminescence spectra (PL). The CaAl₄O₇: Eu²⁺, Dy³⁺ phosphor showed a broad blue emission, peaking at 445 nm when excited at 341 nm. Such a blue emission can be attributed to the intrinsic 4f → 5d transitions of Eu²⁺ in the host lattices. The lifetime decay curve of the Dy³⁺ co‐doped CaAl₄O₇: Eu²⁺ phosphor contains a fast decay component and another slow decay one. Surface morphology also has been studied by SEM. The calculated CIE colour chromaticity coordinates was (0.227, 043). We have also discussed a possible long‐persistent mechanism of CaAl₄O₇:Eu²⁺, Dy³⁺ phosphor. All the results indicate that this phosphor has promising potential for practical applications in the field of long‐lasting phosphors for the purposes of sign boards and defence. Copyright © 2011 John Wiley & Sons, Ltd.     

A promising RVO4:Eu3+,Li+@SiO2 (R = Gd,Y and Gd/Y) red‐emitting phosphor with improved luminescence (cd/m2) and colour purity for optical display applications

Red emission intensity was optimized in three stages, by investigating the effects of: (i) host composition (Gd, Y and Gd/Y), (ii) codoping Li⁺ as a sensitizer and, finally, (iii) with a SiO₂ shell coating as a protecting layer. Lanthanide vanadate powder phosphors were synthesized using a modified colloidal precipitation technique. The effects of SiO₂ coating on phosphor particles were characterized using scanning electron microscopy (SEM)‐EDAX, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and photoluminescence (PL) measurements. An improvement in the PL intensity on Li codoping was due to improved crystallinity, which led to higher oscillating strengths for the optical transitions, and also a lowering of the inversion symmetry of Eu³⁺ ions. Red emission intensity due to ⁵D₀ → ⁵D₂ transition of the phosphor Y_0.94VO₄:Eu³⁺_0.05,Li⁺_0.01 was enhanced by 22.28% compared with Y_0.95VO₄:Eu³⁺_0.05, and was further improved by 58.73% with SiO₂ coating. The luminescence intensity (I) and colour coordinates (x, y) of the optimized phosphor Y_0.94VO₄:Eu³⁺_0.05,Li⁺_0.01@SiO₂, where I = 13.07 cd/m² and (x = 0.6721, y = 0.3240), were compared with values for a commercial red phosphor (Y₂O₂S:Eu³⁺), where I = 27 cd/m² and (x = 0.6522, y = 0.3437). The measured colour coordinates are superior to those of the commercial red phosphor, and moreover, match well with standard NTSC values (x = 0.67, y = 0.33). Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation on luminescence properties of Eu2+‐doped Ba3Al2O5Cl2 phosphor for near‐UV‐excited white LEDs

Ba₃Al₂O₅Cl₂:Eu²⁺ phosphor was prepared by combustion synthesis (CS). The prepared phosphor was excited at 329 nm; the phosphors shows an efficient bluish‐green wide‐band emission centred at 490 nm, which originates from the 4f⁶d¹ → 4f⁷ transition of Eu²⁺ ions. The excitation spectra of the phosphors have a band centred at 329 nm. It was also characterized by XRD, FT–IR for confirmation of phase purity, and FT–IR analysis indicated the vibrations of metal–oxygen (M–O) groups. SEM shows the morphology of the phosphor at the submicron scale. The results indicate that Ba₃Al₂O₅Cl₂:Eu²⁺ phosphor may be applicable for solid‐state lighting purposes. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Design,synthesis and luminescence properties of Ba2YB2O6Cl‐ and Ba2YB2O6F‐based phosphors

Using a high‐temperature solid‐state reaction, the chlorine in Ba₂YB₂O₆Cl is gradually replaced by F, and a new compound with the nominal chemical formula Ba₂YB₂O₆F and two phosphors doped with Ce³⁺ and Eu³⁺, respectively, are obtained. X‐Ray diffraction and photoluminescence spectroscopy are used to characterize the as‐synthesized samples. The as‐synthesized Ba₂YB₂O₆Cl exhibits bright blue emission in the spectral range ~ 330–410 nm with a maximum around 363 nm under X‐ray or UV excitation. Ba₂YB₂O₆F:0.01Ce³⁺ exhibits blue emission in the range ~ 340–570 nm with a maximum around 383 nm. Ba₂YB₂O₆F:0.01Eu³⁺ exhibits a predominantly ⁵D₀–⁷ F₂ emission (~610 nm) and the relative intensities of the ⁵D₀–⁷ F_0,1,2 emissions are tunable under different wavelength UV excitation. The luminescence behaviors of the two phosphors are explained simply in terms of the host composition and site occupancy probability of Ce³⁺ and Eu³⁺, respectively. The results indicate that these phosphors have potential application as a blue phosphor or as a red phosphor. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of red emitting phosphor La2–xEuxLi0.5Al0.5O4 [x = 0.2–2] with K2NiF4 structure

Europium (Eu)³⁺‐substituted La₂Li_0.5Al_0.5O₄ red emitting phosphors were prepared by a conventional high‐temperature solid‐state reaction method. Powder X‐ray diffraction, diffuse reflectance spectra and spectrofluorometry were used as vital characterizing tools for the phosphors. The Eu concentration dependence luminescence properties and Judd–Ofelt intensity parameters were investigated and calculated, respectively. All compositions showed an orange red emission (due to the magnetic and electric dipole transitions of the Eu³⁺ ion) with the appropriate Commission Internationale de l'Eclairage (CIE) colour gamut under near ultraviolet or blue ray light excitation. The calculated critical distance showed that the energy transfer occured between Eu to Eu via an exchange mechanism. The Eu_1.4La_0.6Li_0.5Al_0.5O₄ composition showed the highest red emission intensity with CIE colour saturation compared with that of the commercial Eu‐activated yttrium oxysulfide red phosphor.     

Luminescence in Li3Al2(PO4)3:Eu2+

A series of efficient Li₃Al₂(PO₄)₃:Eu²⁺ novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li₃Al₂(PO₄)₃ phosphor were also investigated. The phosphors were characterized by X‐ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near‐ultraviolet excitation under 310 nm. The emission was observed for Li₃Al₂(PO₄)₃:Eu²⁺ phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu²⁺ was observed in Li₃Al₂(PO₄)₃:Eu²⁺ when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu²⁺ ion by Hg‐free excitation at 310 nm (i.e., solid‐state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Photoluminescence and thermoluminescence properties of Eu2+ doped and Eu2+,Dy3+ co‐doped Ba2MgSi2O7 phosphors

In this work, we report the preparation, characterization, comparison and luminescence mechanisms of Eu²⁺‐doped and Eu²⁺,Dy³⁺‐co‐doped Ba₂MgSi₂O₇ (BMSO) phosphors. Prepared phosphors were synthesized via a high temperature solid‐state reaction method. All prepared phosphors appeared white. The phase structure, particle size, and elemental analysis were analyzed using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and energy‐dispersive X‐ray (EDX) analysis. The luminescence properties of the phosphors were investigated by thermoluminescence (TL) and photoluminescence (PL). The PL excitation and emission spectra of Ba₂MgSi₂O₇:Eu²⁺ showed the peak to be around 381 nm and 490 nm respectively. The PL excitation spectrum of Ba₂MgSi₂O₇:Eu²⁺Dy³⁺ showed the peak to be around 341 nm and 388 nm, and the emission spectrum had a broad band around 488 nm. These emissions originated from the 4f⁶ 5d¹ to 4f⁷ transition of Eu²⁺. TL analysis revealed that the maximum TL intensity was found at 5 mol% of Eu²⁺ doping in Ba₂MgSi₂O₇ phosphors after 15 min of ultraviolet (UV) light exposure. TL intensity was increased when Dy³⁺ ions were co‐doped in Ba₂MgSi₂O₇:Eu²⁺ and maximum TL intensity was observed for 2 mol% of Dy³⁺. TL emission spectra of Ba_1.95MgSi₂O₇:0.05Eu²⁺ and Ba_1.93MgSi₂O₇:0.05Eu²⁺,0.02Dy³⁺ phosphors were found at 500 nm. TL intensity increased with UV exposure time up to 15 min, then decreased for the higher UV radiation dose for both Eu doping and Eu,Dy co‐doping. The trap depths were calculated to be 0.54 eV for Ba_1.95MgSi₂O₇:0.05Eu²⁺ and 0.54 eV and 0.75 eV for Ba_1.93MgSi₂O₇:0.05Eu²⁺,0.02Dy³⁺ phosphors. It was observed that co‐doping with small amounts of Dy³⁺ enhanced the thermoluminescence properties of Ba₂MgSi₂O₇ phosphor. Copyright © 2016 John Wiley & Sons, Ltd. [Correction added on 5 April 2016, after first online publication: The following parts of the abstract have been edited for consistency. '4f65d1' has been corrected to '4f⁶ 5d¹', '4f7' has been corrected to '4f⁷', 'Ba1.95' has been corrected to 'Ba_1.95' and 'Ba1.93' has been corrected to 'Ba_1.93' respectively.]