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.     

Synthesis,characterization and luminescent properties of europium complexes with 2,4,6‐tris‐(2‐pyridyl)‐s‐triazine as highly efficient sensitizers

Using 2,4,6‐tris‐(2‐pyridyl)‐s‐triazine (TPTZ) as a neutral ligand, and p‐hydroxybenzoic acid, terephthalic acid and nitrate as anion ligands, five novel europium complexes have been synthesized. These complexes were characterized using elemental analysis, rare earth coordination titrations, UV/vis absorption spectroscopy and infrared spectroscopy. Luminescence spectra, luminescence lifetime and quantum efficiency were investigated and the mechanism discussed in depth. The results show that the complexes have excellent emission intensities, long emission lifetimes and high quantum efficiencies. The superior luminescent properties of the complexes may be because the triplet energy level of the ligands matches well with the lowest excitation state energy level of Eu³⁺. Moreover, changing the ratio of the ligands and metal ions leads to different luminescent properties. Among the complexes, Eu₂(TPTZ)₂(C₈H₄O₄)(NO₃)₄(C₂H₅OH)·H₂O shows the strongest luminescence intensity, longest emission lifetime and highest quantum efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

Circularly polarized luminescence of Sm (III) and Eu (III) complexes with chiral ligand (R/S)‐BINAPO

Luminescent lanthanide (III) ions have been exploited for circularly polarized luminescence (CPL) for decades. However, very few of these studies have involved chiral samarium (III) complexes. Complexes are prepared by mixing axial chiral ligands (R/S))‐2,2’‐bis(diphenylphosphoryl)‐1,1′‐binaphthyl (BINAPO) with europium and samarium Tris (trifluoromethane sulfonate) (Eu (OTf)₃ and Sm (OTf)₃). Luminescence‐based titration shows that the complex formed is Ln((R/S)‐BINAPO)₂(OTf)₃, where Ln = Eu or Sm. The CPL spectra are reported for Eu((R/S)‐BINAPO)₂(OTf)₃ and Sm((R/S)‐BINAPO)₂(OTf)₃. The sign of the dissymmetry factors, g_em, was dependent upon the chirality of the BINAPO ligand, and the magnitudes were relatively large. Of all of the complexes in this study, Sm((S)‐BINAPO)₂(OTf)₃ has the largest g_em = 0.272, which is one of the largest recorded for a chiral Sm³⁺ complex. A theoretical three‐dimensional structural model of the complex that is consistent with the experimental observations is developed and refined. This report also shows that (R/S)‐BINAPO are the only reported ligands where g_em (Sm³⁺) > g_em (Eu³⁺).     

Synthesis and characterization of Y(1‐x)Eu(x)(TTA)3(Phen) organic luminescent thin films

Yttrium is stoichiometrically doped into europium by mole percentage, during the synthesis of Y_(1‐x)Eu_(x)(TTA)₃(Phen), using solution techniques (where x = 0.2, 0.4, 0.5, 0.6 and 0.8, TTA = thenoyltrifluoroacetone and Phen = 1,10‐phenanthroline).These complexes were characterized using different techniques such as X‐ray diffraction, thermogravimetric/differential thermal analysis, optical absorption and emission spectra. Thin films of the doped Eu–Y complexes were prepared on a glass substrate under a high vacuum of 10^‐6 Torr. The photoluminescence spectra of these thin films were recorded by exciting the sample at a wavelength of 360 nm. The emission peak for all the synthesized complexes centered at 611 nm; maximum emission intensity was obtained from Y_0.6Eu_0.4 (TTA)₃(Phen). The results proved that these doped complexes are more economical than pure Eu(TTA)₃(Phen) and are best suited as red emissive material for energy‐efficient and eco‐friendly organic light‐emitting diodes and displays. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of amlodipine using terbium‐sensitized luminescence in the presence of europium(III) as a co‐luminescence reagent

A sensitive time‐resolved luminescence method for the determination of amlodipine (AM) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of terbium (Tb³⁺) by formation of a ternary complex with AM in the presence of tri‐n‐octylphosphine oxide (TOPO) as co‐ligand, dodecylbenzenesulfate as surfactant and europium ion as a co‐luminescence reagent. The signal for Tb–AM–TOPO is monitored at λ_ex = 242 nm and λ_em = 550 nm. Optimum conditions for the formation of the complex in aqueous system were 0.015 m Tris (hydroxylmethyl) amino methane buffer, pH 9.0, TOPO (1.0 × 10^–4 m ), Eu³⁺ (2.0 × 10^–7 m ), dodecylbenzenesulfate (0.14%) and 6.0 × 10^–5 m of Tb³⁺, which allows the determination of 10–50 ppb of AM with a limit of detection of 1.2 ppb. The relative standard deviations of the method range between 0.1 and 0.2% indicated excellent reproducibility of the method. The proposed method was successfully applied for the assay of AM in pharmaceutical formulations and in plasma samples. Average recoveries of 98.5 ± 0.2% and 95.2 ± 0.2% were obtained for AM in tablet and plasma samples respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of asymmetrical europium(III) complexes involving carbazole, phenanthroline and bathophenanthroline units

Three novel europium complexes, Eu(CCHPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H- carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](1,10-phenanthroline) europium(III), Eu(CCHPD)₃Bath = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](bathophenanthroline) europium(III) and Eu(CPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione](1,10-phenanthroline) europium(III), have been synthesized and characterized (Scheme 1). Involved ligands consist of different chelating and non-chelating units: appended carbazole (Br-Carb), phenanthroline (Phen), bathophenanthroline (Bath) and 1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione (CPD). The luminescence properties show that the carbazole moiety is a better sensitizer for the metal centred (MC) emitting states relative to Phen and Bath. Moreover, its charge-transporting properties make such complexes appealing for their application in electroluminescent devices.     

Photoluminescent properties of Eu3+‐Eu2+ activated MAl2SixO2x + 4 (M = Mg,Ca, Sr,Ba) phosphors prepared in air

In this paper, MAl₂Si_xO_2x+4:Eu²⁺/Eu³⁺ (Eu²⁺ + Eu³⁺ = 2%, molar ratio; M = Mg, Ca, Sr, Ba; x = 0, 0.5, 1, 1.5, 2) phosphors with different SiO₂ concentrations (the ratio of SiO₂ to MAl₂O₄ is n%, n = 0, 50, 100, 150, 200, respectively) were prepared by high‐temperature solid‐state reaction under atmospheric air conditions. Their structures and photoluminescent properties were systematically researched. The results indicate that Eu³⁺ ions have been reduced and Eu²⁺ ions are obtained in air through the self‐reduction mechanism. The alkaline earth metal ions and doping SiO₂ strongly affect the crystalline phase and photoluminescent properties of samples, including microstructures, relative intensity of Eu²⁺ to Eu³⁺, location of emission lines/bands. It is interesting and important that the emission color and intensities of europium‐doped various phosphors which consist of aluminosilicate matrices prepared under atmospheric air conditions could be modulated by changing the kinds of alkaline earth metal and the content of SiO₂.     

Synthesis and optical properties of Eu3+‐substituted glaserite‐type orthovanadates CsK2Y[VO4]2

A new Eu³⁺‐substituted CsK₂Y[VO₄]₂ glaserite‐type orthovanadate phosphor was synthesized by the conventional high temperature solid‐state reaction method. The phase purity was confirmed by powder X‐ray diffraction study and it reveals that all the compositions crystallize in the hexagonal structure. The morphology and elemental composition were measured by FE‐SEM with Energy Dispersive Analysis Of X Rays (EDAX). The band gap is determined by diffuse reflectance spectra. The self‐activated luminescence of the host and Eu³⁺‐substituted luminescence behaviours were studied in detail by photoluminescence spectra. The host CsK₂Y[VO₄]₂ shows green emission, whereas the Eu³⁺‐substituted compositions show red emission. Effect of Eu³⁺ concentrations on the photoluminescence behaviour were also been studied. The Eu³⁺‐doped samples show not only several sharp emission lines but also a broad emission band due to presence of the [VO₄]^3? in the host, which clearly indicates that there is incomplete energy transfer from (VO₄) charge transfer band to Eu³⁺_. The life time of the phosphors also been studied. The Commission Internationale de l'Eclairage (CIE) chromaticity colour coordinates were calculated and it is very much closer to the National Television Standard Committee (NTSC) standards. These investigations evidently reveal that the self‐activated and Eu³⁺‐activated phosphors show a great potential applications as a red phosphor for solid‐state lighting includes white light‐emitting diodes (wLEDs).     

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.     

Effects of slight structural distortion on the luminescence performance in (Ca1‐xEux)WO4 luminescent materials

(Ca_1‐xEu_x)WO₄ (x = 0–21 mol%) phosphors were prepared using the classical solid‐state reaction method. The influence of Eu³⁺ ion doping on lattice structure was observed using powder X‐ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO₄ lattice with a scheelite structure in the form of a Eu³⁺ ion, which introduced a slight lattice distortion into the CaWO₄ matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f–f excitation transitions of Eu³⁺ activators. When the Eu³⁺ concentration was increased to 21 mol%, a local luminescence centre of [WO₄]^2? groups was detected in the matrix and manifested as the decay curves of [WO₄]^2? groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu³⁺ between different energy levels (such as ⁷F₀→⁵L₆, ⁷F₀→⁵D₂) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO₄]^2?→Eu³⁺ was efficient and incomplete.     

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.     

Eu3+‐tetrakis β‐diketonate complexes for solid‐state lighting application

Eu³⁺–β‐diketonate complexes are used, for example, in solid‐state lighting (SSL) or light‐converting molecular devices. However, their low emission quantum efficiency due to water molecules coordinated to Eu³⁺ and low photostability are still problems to be addressed. To overcome such challenges, we synthesized Eu³⁺ tetrakis complexes based on [Q][Eu(tfaa)₄] and [Q][Eu(dbm)₄] (Q1 = C₂₆H₅₆N⁺, Q2 = C₁₉H₄₂N⁺, and Q3 = C₁₇H₃₈N⁺), replacing the water molecules in the tris stoichiometry. The tetrakis β‐diketonates showed desirable thermal stability for SSL and, under excitation at 390 nm, they displayed the characteristic Eu³⁺ emission in the red spectral region. The quantum efficiencies of the dbm complexes achieved values as high as 51%, while the tfaa complexes exhibited lower quantum efficiencies (28–33%), but which were superior to those reported for the tris complexes. The structures were evaluated using the Sparkle/PM7 model and comparing the theoretical and the experimental Judd–Ofelt parameters. [Q1][Eu(dbm)₄] was used to coat a near‐UV light‐emitting diode (LED), producing a red‐emitting LED prototype that featured the characteristic emission spectrum of [Q1][Eu(dbm)₄]. The emission intensity of this prototype decreased only 7% after 30 h, confirming its high photostability, which is a notable result considering Eu³⁺ complexes, making it a potential candidate for SSL.     

Crystal structure and fluorescence of a europium (III) complex: EuCl3(2,2′-bipyridine N,N dioxide) · 2CH3OH

We report the synthesis and characterization of a seven coordinate europium complex, [EuCl₃(C₁₀H₈N₂O₂) ·  2CH₃OH]. The growing interest in developing efficient light conversion molecular devices (LCMDs) necessitates the need for new fluorescent materials. Ideal physicochemical properties of the materials include ligand absorption, efficient metal to ligand transfer, and strong luminescence with a relatively long decay time. The design of such material requires distinct absorbing (ligand) and emitting (metal ion) components. While Eu³⁺ cation has a non-degenerate emitting level, 2,2′-bipyridine N,N dioxide is a heterocyclic ligand known to exhibit strong luminescence. Additional characterization is also described, including single crystal X-ray diffraction, IR and UV-Vis spectroscopies and elemental analysis.     

Rapid determination of gatifloxacin in biological samples and pharmaceutical products using europium‐sensitized fluorescence spectrophotometry

A europium‐sensitized fluorescence spectrophotometry method using an anionic surfactant, sodium dodecyl benzene sulphonate (SDBS), was developed for the determination of gatifloxacin (GFLX). The GFLX–Eu³⁺–SDBS system was studied and it was found that SDBS significantly enhanced the fluorescence intensity of the GFLX–Eu³⁺ complex (about 25‐fold). The optimal experimental conditions were determined as follows: excitation and emission wavelengths of 338 and 617 nm, pH 7.5, 3.0 × 10^–6 mol/L europium(III), and 5.0 × 10^–5 mol/L SDBS. The enhanced fluorescence intensity of the system (ΔI_f) showed a good linear relationship with the concentration of GFLX over the range 1.0 × 10^–8–8.0 × 10^–7 mol/L with a correlation coefficient of 0.9990. The detection limit (S:N = 3) was determined as 1.0 × 10^–9 mol/L. This method has been successfully applied for the determination of GFLX in pharmaceuticals and human urine/serum samples. Compared with most other methods reported, the rapid and simple procedure proposed here offered higher sensitivity, wider linear range and good stability. The luminescence mechanism of the system is also discussed in detail. Copyright © 2008 John Wiley & Sons, Ltd.     

The luminescent properties and crystal structure of Sr(1.5‐x)‐(1.5y)Mg0.5SiO4:xEu2+,yCe3+ blue phosphor synthesized by co‐precipitation method

In order to improve the luminescent performance of silicate blue phosphors, Sr_{(1.5‐x)‐(1.5y)}Mg_0.5SiO₄:xEu²⁺,yCe³⁺ phosphors were synthesized using one‐step calcination of a precursor prepared by chemical co‐precipitation. The crystal structure and luminescent properties of the phosphors were analyzed using X‐ray diffraction and fluorescence spectrophotometry, respectively. Because the activated ions (Eu²⁺) can occupy two different types of sites (Sr₁ and Sr₂), the emission spectrum of Eu²⁺ excited at 350 nm contains two single bands (EM₁ and EM₂) in the wavelength range 400–550 nm, centered at 463 nm, and the emission intensity first increases and then decreases with increasing concentrations of Eu²⁺ ions. Co‐doping of Ce³⁺ ions can greatly enhance the emission intensity of Eu²⁺ by transferring its excitation energy to Eu²⁺. Because of concentration quenching, a higher substitution concentration of Ce³⁺ can lead to a decrease in the intensity. Meanwhile, the quantum efficiency of the phosphor is improved after doping with Ce³⁺, and a blue shift phenomenon is observed in the CIE chromaticity diagram. The results indicate that Sr_{(1.5‐x)‐(1.5y)}Mg_0.5SiO₄:xEu²⁺,yCe³⁺ can be used as a potential new blue phosphor for white light‐emitting diodes.     

Synthesis,density functional theory calculations and luminescence of lanthanide complexes with 2,6‐bis[(3‐methoxybenzylidene)hydrazinocarbonyl] pyridine Schiff base ligand

A pyridine‐diacylhydrazone Schiff base ligand, L = 2,6‐bis[(3‐methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X‐ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO₃)₂]NO₃.xH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra‐red (FT‐IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO₃)₂]⁺ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT‐IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.     

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.     

Efficient solution‐processed double‐layer red OLEDs based on a new europium complex with a carbazole group

A new europium complex EuL₃(Phen) was used as guest dopant, and a blend of Polyvinylcarbazole and 2‐(biphenyl‐4‐yl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (PVK and PBD) as host matrix. Efficient red organic light‐emitting devices (OLEDs) with double‐layer structures were manufactured via a solution‐processed technique. The guest‐doped levels were 1, 3 and 5 wt% relative to the blend mass, respectively. For the 1 wt% doping‐level device, the luminous efficiency and luminance were up to 2.96 cd/A and 635.78 cd/m² with emissions from both EuL₃(Phen) and from the host; for the 3 wt% doping‐level device, the maximum luminous efficiency and luminance were 1.01 cd/A and 370.91 cd/m² for the single emission from EuL₃(Phen) only. Copyright © 2014 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.     

Spectral investigations on Eu3+,Sm3+‐doped and Sm3+/Eu3+ co‐doped potassium‐fluoro‐phosphate glass emitting intense orange‐red for lighting applications

Potassium fluoro‐phosphate (KFP) glass singly doped with different concentrations of europium (Eu³⁺) or samarium (Sm³⁺) or co‐doped (Sm³⁺/Eu³⁺) was prepared, and their luminescence spectra were investigated. The phase composition of the product was verified by X‐ray diffraction analysis. Optical transition properties of Eu³⁺ in the studied potassium phosphate glass were evaluated in the framework of the Judd–Ofelt theory. The radiative transition rates (A_R), fluorescence branching ratios (β), stimulated emission cross‐sections (σ_e) and lifetimes (τ_exp) for certain transitions or levels were evaluated. Red emission of Eu³⁺ was exhibited mainly by the ⁵D₀→⁷F₂ transition located at 612 nm. Concentration quenching and energy transfer were observed from fluorescence spectra and decay curves, respectively. It was found that the lifetimes of the ⁵D₀ level increased with increase in concentration and then decreased. By co‐doping with Sm³⁺, energy transfer from Sm³⁺ to Eu³⁺ occurred and contributed to the enhancement in emission intensity. Intense orange‐red light emission was obtained upon sensitizing with Sm³⁺ in KFP glass. This approach shows significant promise for use in reddish‐orange lighting applications. The optimized properties of the Sm³⁺/Eu³⁺ co‐doped potassium phosphate glass might be promising for optical materials.