Synthesis and characterization of novel europium β‐diketonate organic complexes for solid‐state lighting

Volatile Eu complexes, namely Eu(TTA)₃Phen, Eu_(x)Y_(1‐x)(TTA)₃ Phen; Eu_(x)Tb_(1‐x)(TTA)₃Phen; Eu, europium; Y, yttrium; Tb, Terbium; TTA, thenoyltrifluoroacetone; and Phen, 1,10 phenanthroline were synthesized by maintaining stichiometric ratio. Various characterization techniques such as X‐ray diffraction (XRD), photoluminescence (PL) and thermo gravimetric analysis/differential thermal analysis (TGA/DTA) were carried out for the synthesized complexes. Diffractograms of all the synthesized complexes showed well‐resolved peaks, which revealed that pure and doped organic Eu³⁺ complexes were crystalline in nature. Of all the synthesized complexes, Eu_0.5 Tb_0.5(TTA)₃Phen showed maximum peak intensity, while the angle of maximum peak intensity for all complexes was almost the same with slightly different d‐values. A prominent sharp red emission line was observed at 611 nm when excited with light at 370 nm. It was observed that the intensity of red emissions increased for doped europium complexes Eu_(x)Y_(1‐x)(TTA)₃Phen and Eu_(x)Tb_(1‐x)(TTA)₃ Phen, when compared with Eu complexes. Emission intensity increased in the following order: Eu(TTA)₃Phen > Eu_0.5 Tb_0.5(TTA)₃Phen > Eu_0.4 Tb_0.6(TTA)₃Phen > Eu_0.5Y_0.5(TTA)₃Phen > Eu_0.4Y_0.6(TTA)₃Phen, proving their potential application in organic light‐emitting diodes (OLEDs). TGA showed that Eu complexes doped in Y³⁺ and Tb³⁺ have better thermal stability than pure Eu complex. DTA analysis showed that the melting temperature of Eu(TTA)₃ Phen was lower than doped Eu complexes. These measurements infer that all complexes were highly stable and could be used as emissive materials for the fabrication of OLEDs. Copyright © 2012 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.     

Luminescence of Eu and Ce in K3Ca2(SO4)3F fluoride material

A new halophosphor K₃Ca₂(SO₄)₃ F activated by Eu or Ce and K₃Ca₂(SO₄)₃ F:Ce,Eu co‐doped halosulfate phosphor has been synthesized by the co‐precipitation method and characterized for its photoluminescence (PL). The PL emission spectra of the K₃Ca₂(SO₄)₃ F :Ce phosphor show emission at 334 nm when excited at 278 nm due to 5d → 4f transition of Ce³⁺ ions. In the K₃Ca₂(SO₄)₃ F:Eu lattice, Eu²⁺ (440 nm) as well as Eu³⁺ (596 nm and 615 nm) emissions have been observed showing ⁵D₀ → ⁷ F₁ and ⁵D₀ → ⁷ F₂ transition of the Eu³⁺ ion, which is in the blue and red region of the visible spectrum respectively. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems owing to its non‐degenerate emitting ⁵D₀ state. K₃Ca₂(SO₄)₃ F:Ce,Eu is suitable for Ce³⁺ → Eu²⁺ → Eu³⁺ energy transfer in which Ce³⁺and Eu²⁺ play the role of sensitizers and Eu²⁺ and Eu³⁺ act as the activators. The observations presented in this paper are relevant for lamp phosphors. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of different temperatures to remove reduction gas on the photoluminescence properties of Eu‐doped Li2(Ba1‐xSrx)SiO4 phosphors

In this study, Eu‐doped Li₂(Ba_1‐xSr_x)SiO₄ powders (x = 0, 0.2, 0.4, and 0.6) were synthesized at 850°C in a reduction atmosphere (5% H₂ + 95% N₂) for a duration of 1 h using a solid‐state reaction method. The reduction atmosphere was infused as the synthesis temperature reached 850°C, and was removed as the temperature dropped to 800–500°C. Li₂(Ba_1‐xSr_x)SiO₄ (or Li₂BaSiO₄), (Ba,Sr)₂SiO₄ (or BaSiO₄), and Li₄SiO₄ phases co‐existed in the synthesized Eu‐doped Li₂(Ba_1‐xSr_x)SiO₄ powders. A new finding was that the reduction atmosphere removing (RAR) temperature of the Li₂(Ba_1‐xSr_x)SiO₄ phosphors had a large effect on their photoluminescence excitation (PLE) and PL properties. Except for the 800°C‐RAR‐treated Li₂BaSiO₄ phosphor, PLE spectra of all other Li₂(Ba_1‐xSr_x)SiO₄ phosphors had one broad emission band with two emission peaks centred at ~242 and ~283 nm; these PL spectra had one broad emission band with one emission peak centred at 502–514 nm. We showed that the 800°C‐RAR‐treated Li₂BaSiO₄ phosphor emitted a red light and all other Li₂(Ba_1‐xSr_x)SiO₄ phosphors emitted a green light. Reasons for these results are discussed thoroughly.     

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.     

Synthesis,photophysics, electrochemistry,thermal stability and electroluminescent performances of a new europium complex with bis(β‐diketone) ligand containing carbazole group

We synthesized a new europium complex [Eu(ecbpd)₃(Phen)] with bis(β‐diketone) ligand containing a carbazole group, in which ecbpd and Phen are dehydro‐3,3′‐(9‐ethyl‐9H‐carbazole‐3,6‐diyl)bis(1‐phenylpropane‐1,3‐dione) and 1,10‐phenanthroline, respectively. Its UV/vis and photoluminescent spectra, quantum yield, luminescence lifetime, electrochemistry, thermal stability and electroluminescent performances were studied. This europium complex showed low efficiency luminescence, which is probably due to the mismatching energy levels of its ligand and Eu³⁺, as well as the double Eu³⁺ core resonance.     

Synthesis and luminescence properties of a blue-emitting Sr(3.5) Y(6.5) O(2) (PO(4) )(1.5) (SiO(4) )(4.5) :Eu(2+) phosphor

A novel blue‐emitting Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:Eu²⁺ phosphor was synthesized via a solid‐state reaction. Powder X‐ray diffraction (XRD) analysis demonstrated that the Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5 host had a hexagonal crystal structure in the space group P6₃/m and unit cell parameters a = 9.418 Å, c = 6.900 Å. The as‐prepared phosphor showed a blue emission and all the main emission peaks were located at around 466 nm for different excitation wavelengths of 297, 333 and 391 nm. The temperature dependence of the photoluminescence property was investigated in the range 20–250 °C, and the emission intensity decreased to 71% of the initial value at room temperature on increasing the temperature to 150 °C. According to the classical theory of fluorescent thermal quenching, the activation energy (ΔE) for the thermal quenching luminescence of the as‐prepared Sr_3.45Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:0.05Eu²⁺ phosphor was determined to be 0.20 eV. Copyright © 2011 John Wiley & Sons, Ltd.     

Luminescent properties of sol–gel processed red‐emitting phosphor Ca0.6Sr0.4–1.5x‐0.5yMo0.4 W0.6O4:EuxLiy

A series of red‐emitting phosphors Ca_0.6Sr_{0.4–1.5x‐0.5y}Mo_0.4 W_0.6O₄:Eu_xLi_y (x = 0.02–0.12, y = 0–0.12) has been synthesized by a sol‐gel method. The effects of calcining temperature, concentrations of Li⁺ and Eu³⁺, and compensation ions on the luminescent properties were investigated. X‐ray diffraction and scanning electron microscopic results showed that as‐prepared phosphors were of single phase with several microns. The Li⁺ compensated compositions showed remarkably intense red emission at 619 nm. The emission intensity of the series reached maximum for compositions at x = 0.08 and y = 0.08 when the calcining temperature was 900 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

A dinuclear europium(III) complex with thenoyltrifluoroacetonato and 1-(2-pyridylzao)-2-naphtholato ligands and its optical properties

Dinuclear lanthanide complexes of the general for Ln₂(TTA)₄(PAN)₂ (Ln = Eu, Gd, Tb, Yb; TTA and monodeprotonated thenoyltrifluoroacetone and PAN 1-(2-pyridylazo)-2-naphthol, respectively) were prepared and structurally characterized. These novel complexes, representing the first examples of crystallographically characterized lanthanide-PAN complexes, each feature a dinuclear core with the metal atoms bridged by the phenolato O atoms of the chelating-bridging PAN ligands. Electronic spectroscopic and photoluminescence studies were carried out for the Eu(III) complex, and the results are consistent with ligand-mediated energy transfer and ligand-sensitized luminescence characteristic of Eu(III). The Eu(III) complex doped into a polymeric film was shown to effectively limit a nanosecond 523-nm laser pulse, and the limiting effect is rationalized in terms of reverse saturable absorption due to the strong absorption of the metal’s excited triplet states that are populated by intersystem crossing.     

Structural and optical properties of europium‐ and titanium‐doped Y2O3 nanoparticles

Luminescent nanoparticles of Y₂O₃ doped with europium (Eu) and/or titanium (Ti) were synthesized using modified sol–gel routes. The crystalline cubic phase was confirmed using X‐ray powder diffraction (XRD). Particle morphology and size were evaluated using scanning and transmission electron microscopy. High‐resolution transmission electron microscopy showed that the synthesis method affected the average particle size and the Fourier transform of the images showed the lattice plane distances, indicating that the samples presented high crystallinity degree in accordance with the XRD pattern. The Ti valence was investigated using X‐ray absorption near edge spectroscopy and the tetravalent form was the dominant oxidizing state in the samples, mainly in Eu and Ti co‐doped Y₂O₃. Optical behaviour was investigated through X‐ray excited optical luminescence and photoluminescence under ultraviolet–visible (UV–vis) and vacuum ultraviolet (VUV) excitation. Results indicated that Eu³⁺ is the emitting centre in samples doped with only Eu and with both Eu and Ti with the ⁵D₀→⁷F₂ transition as the most intense, indicating Eu³⁺ in a noncentrosymmetric site. Finally, in the Eu,Ti‐doped Y₂O₃ system, Ti³⁺ (or Ti^IV) excitation was observed but no Ti emission was present, indicating a very efficient energy transfer process from Ti to Eu³⁺. These results can aid the development of efficient nanomaterials, activated using UV, VUV, or X‐rays.     

Eu2+‐induced enhancement of defect luminescence of ZnS

The Eu²⁺‐induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460 nm and 520 nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λ_ex > 337 nm (the bandgap energy 3.68 eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365 nm and 410 nm. Compared with ZnS nanophosphors, the 520 nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460 nm and 520 nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu²⁺ intra‐ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520 nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu²⁺ acceptor‐bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non‐radiative electronic relaxation and thus increases the intensity of the 460 nm and 520 nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu²⁺‐doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.     

Structural and luminescence properties of Y2‐xGeMoO8:REx (RE = Eu,Tb) phosphors

Y_2‐xGeMoO₈:RE_x (RE = Eu, Tb) phosphors were synthesized using a facile sol–gel method. The morphology and structure of the phosphors were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD); while their luminescent properties were investigated by photoluminescence (PL) spectrometry. Our results reveal that all of these Y_2‐xGeMoO₈:RE_x (RE = Eu, Tb) phosphors adopted the tetragonal phase, belonging to Scheelite (CaWO₄) structure. The obtained YGeMoO₈:Eu phosphors exhibit a strong emission in the red light range which can be assigned to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ when it is excited at 459 nm. Under 392 and 489 nm excitation, the YGeMoO₈:Tb phosphors present predominant green emission (⁵D₄ → ⁷F₅) at 540 nm. The highest emission of the phosphors can be achieved by adjusting the doping concentration to be 0.25 for Eu³⁺ and 0.15 for Tb³⁺, respectively. The promising luminescence properties of these materials indicate that they can be potentially applied to white‐light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and luminescence of Eu3+‐doped in triple phosphate Ca8MgBi(PO4)7 with whitlockite structure

Triple whitlockite‐type structure‐based red phosphors Ca₈MgBi_1?x(PO₄)₇:xEu³⁺ (x = 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 1.00) were synthesized by a conventional solid‐state reaction route and characterized by their X‐ray crystal structures. The X‐ray diffraction (XRD) patterns, Fourier transform infrared spectra, morphologies, photoluminescence spectra, UV/Vis reflectance spectra, decay times and the International Commission on Illumination (CIE) chromaticity coordinates of Ca₈MgBi_1?x(PO₄)₇:xEu³⁺ were analyzed. Eu‐doped Ca₈MgBi(PO₄)₇ phosphors exhibited strong red luminescence with peaks at 616 nm due to the ⁵D₀ → ⁷ F₂ electric dipole transition of Eu³⁺ ions after excitation at 396 nm. The UV/Vis spectra indicated that the band gap of Ca₈MgBi_0.30(PO₄)₇:0.70Eu³⁺ is larger than that of Ca₈MgBi(PO₄)₇. The phosphor developed in this study has great potential as a red‐light‐emitting phosphor for UV light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence characteristics of (Y,Gd)BO3:RE (RE = Eu3+, Ce3+, Dy3+ and Tb3+) phosphors for blue chip and near‐UV white LEDs

A series of Eu³⁺‐, Ce³⁺‐, Dy³⁺‐ and Tb³⁺‐doped (Y,Gd)BO₃ phosphors was synthesized by a solid‐state diffusion method. X‐Ray diffraction confirmed their hexagonal structure and the scanning electron microscopy results showed crystalline particles. The excitation spectra revealed that (Y,Gd)BO₃ phosphors doped with Eu³⁺, Ce³⁺ , Dy³⁺ and Tb³⁺ are effectively excited with near UV‐light of 395 nm/blue light, 364, 351 and 314 nm, respectively. Photoluminescence spectra of Eu³⁺‐, Ce³⁺‐ and Tb³⁺/Dy³⁺‐doped phosphor showed intense emission of reddish orange, blue and white light, respectively. The phosphor Y_0.60Gd_0.38BO₃:Ce_0.02 showed CIE 1931 color coordinates of (0.158, 0.031) and better color purity compared with commercially available blue BAM:Eu²⁺ phosphor. The phosphor (Y,Gd)BO₃ doped with Eu³⁺, Dy³⁺ and Tb³⁺ showed CIE 1931 color coordinates of (0.667, 0.332), (0.251, 0.299) and (0.333, 0.391) respectively. Significant photoluminescence characteristics of the prepared phosphors indicate that they might serve as potential candidates for blue chip and near‐UV white light‐emitting diode applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhancing the luminescence of Eu3+/Eu2+ ion‐doped hydroxyapatite by fluoridation and thermal annealing

This paper reports a novel way for the synthesis of a europium (Eu)‐doped fluor‐hydroxyapatite (FHA) nanostructure to control the luminescence of hydroxyapatite nanophosphor, particularly, by applying optimum fluorine concentrations, annealed temperatures and pH value. The Eu‐doped FHA was made using the co‐precipitation method followed by thermal annealing in air and reducing in a H₂ atmosphere to control the visible light emission center of the nanophosphors. The intensities of the OH^? group decreased with the increasing fluorine concentrations. For the specimens annealed in air, the light emission center of the nanophosphor was 615 nm, which was emission from the Eu³⁺ ion. However, when they were annealed in reduced gas (Ar + 5% H₂), a 448 nm light emission center from the Eu²⁺ ion of FHA was observed. The presence of fluorine in Eu‐doped FHA resulted in a significant enhancement of nanophosphor luminescence, which has potential application in light emission and nanomedicine.     

Photoluminescence properties of LiBaPO4:M3+ phosphor for near‐UV light‐emitting diode (M = Eu and Dy)

A novel phosphor LiBaPO₄ doped with rare earths Eu and Dy prepared by high temperature solid‐state reaction method is reported. The phosphors were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The emission and excitation spectra of these materials were measured at room temperature with a spectrofluorophotometer. The excitation spectra of LiBaPO₄:Eu³⁺ phosphor can be efficiently excited by 394 nm, which is matched well with the emission wavelength of near‐UV light‐emitting diode (LED) chip. PL properties of Eu³⁺‐doped LiBaPO₄ exhibited the characteristic red emission coming from ⁵D₀ → ⁷ F₁ (593 nm) and ⁵D₀ → ⁷ F₂ (617 nm) electronic transitions with color co‐ordinations of (0.680, 0.315). The results demonstrated that LiBaPO₄:Eu³⁺ is a potential red‐emitting phosphor for near‐UV LEDs. Emission spectra of LiBaPO₄:Dy³⁺ phosphors showed efficient blue (481 nm) and yellow (574 nm) bands, which originated from ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions of the Dy³⁺ ion, respectively. The 574 nm line is more intense than the 481 nm lines, which indicates that the site Dy³⁺ is located with low symmetry. This article summarizes fundamentals and possible applications of optically useful inorganic phosphates with visible photoluminescence of Eu³⁺ and Dy³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

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.     

Photoluminescence properties of LiTi2 − xEux(PO4)3 phosphor

A solid‐state reaction route‐based LiTi_{2 ? x}Eu_x(PO₄)₃ was phosphor synthesized for the first time to evaluate its luminescence performance by excitation, emission and lifetime (τ) measurements. The LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor was excited at λ_exci. = 397 nm to give an intense orange–red (597 nm) emission attributed to the ⁵D₀ → ⁷F₁ magnetic dipole (ΔJ = ±1) transition and red (616 nm) emission (⁵D₀ → ⁷F₂), which is an electric dipole (ΔJ = ±2) transition of the Eu³⁺ ion. Beside this, excitation and emission spectra of host LiTi₂(PO₄)₃ powder were also reported. The effect of Eu³⁺ concentration on luminescence characteristics was explained from emission and lifetime profiles. Concentration quenching in the LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor was studied from the Dexter's model. Dipole–quadrupole interaction is found to be responsible for energy transfer among Eu³⁺ ions in the host lattice. The LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor displayed a reddish‐orange colour realized from a CIE chromaticity diagram. We therefore suggest that this new phosphor could be used as an optical material of technological importance in the field of display devices. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel red colour emitting Ca0.995Mg2(SO4)3:0.5Eu2+ phosphor under ultraviolet,blue, and green excitation for plant growth LEDs

In the recent few years, Eu²⁺- and Mn⁴⁺-activated phosphors are widely used as potential colour converters for indoor plant cultivation lighting application due to their marvellous luminescence characteristics as well as low cost. In this investigation, we synthesized novel red colour-emitting Ca_(2−x)Mg₂(SO₄)₃:xmol% Eu²⁺ (x = 0–1.0 mol%) phosphors via a solid-state reaction method in a reducing atmosphere. The photoluminescence (PL) excitation spectra of synthesized phosphors exhibited a broad excitation band with three excitation bands peaking at 349 nm, 494 nm, and 554 nm. Under these excitations, emission spectra exhibited a broad band in the red colour region at ~634 nm. The PL emission intensity was measured for different concentrations of Eu²⁺. The maximum Eu²⁺ doping concentration in the Ca₂Mg₂(SO₄)₃ host was observed for 0.5 mol%. According to Dexter theory, it was determined that dipole–dipole interaction was responsible for the concentration quenching. The luminous red colour emission of the sample was confirmed using Commission international de l'eclairage colour coordinates. The results of PL excitation and emission spectra of the prepared phosphors were well matched with excitation and emission wavelengths of phytochrome P_R. Therefore, from the entire investigation and obtained results it was concluded that the synthesized Ca_0.995Mg₂(SO₄)₃:0.5mol%Eu²⁺ phosphor has huge potential for plant cultivation application.