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.     

Luminescence properties of a novel red phosphor 6LaPO4–3La3PO7–2La7P3O18:Eu3+

Eu³⁺‐doped 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈ red luminescent phosphors were synthesized by co‐deposition and high‐temperature solid‐state methods and its polyphase state was confirmed by X‐ray diffraction analysis. Transmission electron microscopy showed the grain morphology as a mixture of rods and spheres. Luminescence properties of the phosphor were investigated and its red emission parameters were evaluated as a function of Eu³⁺ concentration (3.00–6.00 mol%). Excitation spectra of 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈:Eu³⁺ showed strong absorption bands at 280, 395, and 466 nm, while the luminescence spectra exhibited prominent red emission peak centred at 615 nm (⁵D₀→⁷F₂) in the red region. CIE chromaticity coordinates of the 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈:5%Eu³⁺ phosphor were (0.668, 0.313) in the red region, and defined its potential application as a 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.     

Eu3+–Eu2+‐doped xAl2O3–ySiO2 and xAl2O3–zMgO composites phosphors

In this paper, the Eu³⁺–Eu²⁺ (4%, molar ratio)‐doped xAl₂O₃–ySiO₂ (x = 0–2.5, y = 1–5) and xAl₂O₃–zMgO (x = 0–1.5, z = 0–3) composites phosphors with different Al₂O₃ to SiO₂ (A/S) and Al₂O₃ to MgO (A/M) ratios were prepared using a high‐temperature solid‐state reaction under air atmosphere. The effects of the A/S and A/M on luminescence properties, crystal structure, electron spin resonance, and Commission Internationale de l’Eclairage chromaticity coordinates of the samples were systematically analyzed. These results indicated that the different A/S and A/M ratios in the matrix effectively affected the crystal phase, degrees of self‐reduction of Eu³⁺, and led the relative emission intensity of Eu²⁺/Eu³⁺ to change and adjust.     

Photoluminescence properties of Ca2Al2O5:RE3+ (RE = Eu,Dy and Tb) phosphors for solid state lighting

Ca₂Al₂O₅:Eu³⁺, Ca₂Al₂O₅:Dy³⁺ and Ca₂Al₂O₅:Tb³⁺ phosphors were synthesized using a combustion synthesis method. The prepared phosphors were characterized by X‐ray powder diffraction for phase purity, by scanning electron microscopy for morphology, and by photoluminescence for emission and excitation measurements. The Ca₂Al₂O₅:Eu³⁺ phosphors could be efficiently excited at 396 nm and showed red emission at 594 nm and 616 nm due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions. Dy³⁺‐doped phosphors showed blue emission at 482 nm and yellow emission at 573 nm. Ca₂Al₂O₅:Tb³⁺ phosphors showed emission at 545 nm when excited at 352 nm. Concentration quenching occurred in both Eu³⁺ and Dy³⁺phosphors at 0.5 mol%. Photoluminescence results suggested that the aluminate‐based phosphor could be a potential candidate for application in environmentally friendly based lighting technologies.     

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.     

Mechanoluminescence properties of SrAl2O4:Eu2+ phosphor by combustion synthesis

In this paper, europium‐doped strontium aluminate (SrAl₂O₄:Eu²⁺) phosphors were synthesized using a combustion method with urea as a fuel at 600°C. The phase structure, particle size, surface morphology and elemental analysis were studied using X‐ray diffractometry (XRD), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectra. The EDX and FTIR spectra confirm the elements present in the SrAl₂O₄:Eu²⁺ phosphor. The optical properties of SrAl₂O₄:Eu²⁺ phosphors were investigated by photoluminescence (PL) and mechanoluminescence (ML). The excitation and emission spectra showed a broad band with peaks at 337 and 515 nm, respectively. The ML intensities of SrAl₂O₄:Eu²⁺ phosphor increased proportionally with the increase in the height of the mechanical load, which suggests that this phosphor could be used in stress sensors. The CIE colour chromaticity diagram and ML spectra confirm that the SrAl₂O₄:Eu²⁺ phosphor emitted green coloured light. Copyright © 2015 John Wiley & Sons, Ltd.     

Intense green‐, red‐emitting Tb3+, Tb3+/Bi3+‐doped and Sm3+, Sm3+/La3+‐doped Ca2Al2SiO7 phosphors

This paper focuses on an optical study of a Tb³⁺/Bi³⁺‐doped and Sm³⁺/La³⁺‐ doped Ca₂Al₂SiO₇ phosphor synthesized using combustion methods. Here, Ca₂Al₂SiO₇:Sm³⁺ showed a red emission band under visible light excitation but, when it co‐doped with La³⁺ ions, the emission intensity was further enhanced. Ca₂Al₂SiO₇:Tb³⁺ shows the characteristic green emission band under near‐ultraviolet light excitation wavelengths, co‐doping with Bi³⁺ ions produced enhanced photoluminescence intensity with better colour tunable properties. The phosphor exhibited better phase purity and crystallinity, confirmed by X‐ray diffraction. Binding energies of Ca(2p), Al(2p), Si(2p), O(1s) were studied using X‐ray photoelectron spectroscopy. The reported phosphor may be a promising visible light excited red phosphor for light‐emitting diodes and energy conversion devices.     

Study on luminescence properties of Ce3+ and Eu3+ ions in a nanocrystalline hexagonal Zn4Al22O37 novel system

The present communication is strongly focused on the investigation of synthesis, structural and luminescence properties of cerium (Ce³⁺)- and europium (Eu³⁺)-activated Zn₄Al₂₂O₃₇ phosphors. Ce³⁺- and Eu³⁺-doped Zn₄Al₂₂O₃₇ novel phosphors were prepared using a solution combustion synthesis route. Structural properties were studied using powder X-ray diffraction and high-resolution transverse electron microscopy. The optical properties were studied using ultraviolet–visible light spectroscopy and Fourier transform infrared spectroscopy; luminescence properties were studied using a photoluminescence (PL) technique. The crystal structure of the prepared Zn₄Al₂₂O₃₇ host and Ce³⁺- and Eu³⁺-activated Zn₄Al₂₂O₃₇ phosphors was investigated and was found to have a hexagonal structure. The measured PL emission spectrum of the Ce³⁺-doped Zn₄Al₂₂O₃₇ phosphor showed an intense and broad emission band centred at 421 nm under a 298 nm excitation wavelength. By contrast, the Eu³⁺-doped Zn₄Al₂₂O₃₇ phosphor exhibited two strong and intense emission bands at approximately 594 nm (orange) and 614 nm (red), which were monitored under 395 nm excitation. The Commission Internationale de l’Eclairage (CIE) colour coordinates of the Ce³⁺-doped Zn₄Al₂₂O₃₇ were investigated and found to be x = 0.1567, y = 0.0637 (blue) at 421 nm and for Eu³⁺-doped Zn₄Al₂₂O₃₇ were x = 0.6018, y = 0.3976 (orange) at 594 nm and x = 0.6779, y = 0.3219 (red) at 614 nm emission. The luminescence behaviour of the synthesized phosphors suggested that these phosphors may be used in lighting applications.     

Synthesis and photoluminescence properties of Eu3+‐activated Ba2Mg(PO4)2 phosphor

In this paper, we have reported the photoluminescence (PL) properties of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor synthesized using a wet chemical method. The preliminary scanning electron microscopy (SEM) investigation of the sample revealed irregular surface morphology with particle sizes in the 10–50 μm range. The strongest PL excitation peak was observed at 396 nm. The emission spectra indicated that this phosphor can be effectively excited by the 396 nm wavelength. Upon 396 nm excitation, the emission spectrum showed characteristics peaks located at 592 nm and 615 nm. These intense orange‐red emission peaks were obtained due to f→f transitions of Eu³⁺ ions. The emission peak at 592 nm is referred to as the magnetic dipole ⁵D₀→⁷F₁ transition and the emission peak at 615 nm corresponded to the electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺. The Commission Internationale de l’Eclairage (CIE) coordinates of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor were found to be (0.586, 0.412) for wavelength 592 nm and (0.680, 0.319) for wavelength 615 nm situated at the edge of the CIE diagram, indicating high colour purity of phosphors. Due to the high emission intensity and a good excitation profile, Eu³⁺‐doped Ba₂Mg(PO₄)₂ phosphor may be a promising orange‐red phosphor candidate for solid‐state lighting applications.     

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.     

Luminescence studies on Al4B2O9:Eu2+ phosphor crystals

A novel blue‐emitting phosphor, Eu²⁺‐doping Al₄B₂O₉, was prepared via a modified solid‐state reaction. Al₄B₂O₉:Eu²⁺ nanoparticles with diameters varying in a range from 20 to 50 nm were obtained using urea as an auxiliary reagent at the optimum temperature of 850°C. The crystallization and particle sizes of Al₄B₂O₉:Eu²⁺ were investigated using powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence (PL) results showed that Al₄B₂O₉:Eu²⁺ phosphor could be efficiently excited by the ultraviolet region from 240 to 410 nm, exhibiting bright blue emission. Further investigation on concentration‐dependent emission spectra indicated that the Al_3.997B₂O₉:Eu²⁺_0.003 phosphor exhibited the strongest luminescent, and the relative PL intensity decreased with increasing Eu²⁺ concentration due to concentration quenching. In addition, the concentration quenching for the one‐Eu‐site emission centers was caused by the electric multipole–multipole interaction. Copyright © 2010 John Wiley & Sons, Ltd.     

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 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 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).     

Sol–gel synthesis and luminescence property of Sr4Al2O7:Re3+,R+ (Re = Eu and Dy; R = Li,Na and K) phosphors for white LEDs

Sr₄Al₂O₇:Eu³⁺ and Sr₄Al₂O₇:Dy³⁺ phosphors with alkali metal substitution were prepared using a sol–gel method. The effects of a charge compensator R on the structure and luminescence of Sr₄Al₂O₇:Re³⁺,R⁺ (Re = Eu and Dy; R = Li, Na and K) phosphors were investigated in detail. Upon heating to 1400°C, the structure of the prepared samples was that of the standard phase of Sr₄Al₂O₇. Under ultraviolet excitation, all Sr₄Al₂O₇:Eu³⁺,R⁺ samples exhibited several narrow emission peaks ranging from 550 to 700 nm due to the 4f → 4f transition of Eu³⁺ ions. All Sr₄Al₂O₇:Dy³⁺,R⁺ phosphors showed two emission peaks at 492 and 582 nm, due to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, respectively. The luminescence intensity of Sr₄Al₂O₇:Re³⁺,R⁺ (Re = Eu and Dy; R = Li, Na and K) phosphors improved markedly upon the addition of charge compensators, promoting their application in white light‐emitting diodes with a near‐ultraviolet chip.     

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.     

Sol–gel preparation and luminescent properties of red‐emitting phosphor Sr‐Ba‐Mo‐W‐O‐(Eu3+,Sm3+)

Two series of red‐emitting phosphors Sr‐Ba‐Mo‐W‐O:Eu,Sm and Sr‐Ba‐Mo‐W‐O:Eu have been synthesized by a sol–gel method. The effects of the chemical composition, concentrations of Sm³⁺ and Eu³⁺, the Sr²⁺/Ba²⁺ ratio, and the W⁶⁺/Mo⁶⁺ ratio on the luminescent properties were investigated. The as‐prepared phosphors were characterized by X‐ray diffraction and Raman spectra. Results showed that single phases of the two series were prepared. The compositions of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 had the strongest luminescent intensity. The excitation spectra of Sm³⁺, Eu³⁺ co‐doped phosphors were broader and the strongest peak moved to 404 nm when compared with that of Eu³⁺ single‐doped phosphors. The luminescent intensity of the Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 at 618 nm were 2.8 times greater than that of Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10. The luminescent intensity of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 at 150 °C decreased to 56.8% and 50.3% of the initial value at room temperature, respectively. Copyright © 2015 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.     

Influence of Tl+ activator ions on the luminescence characteristics of KCl0.5Br0.5:Eu2+ powder phosphors

Photoluminescence (PL) of thallium co‐doped with KCl_0.5Br_0.5:Eu²⁺ powder phosphors display emission bands at 320 and 370 nm attributable to centres involving Tl⁺ ions in addition to characteristic Eu²⁺ emission around 420 nm. Additional PL excitation and emission bandS observed around 260 and 380 nm, respectively, were observed in the double‐doped KCl_0.5Br_0.5:Eu²⁺, Tl⁺ powder phosphors and are attributed to complex centres involving Tl⁺ and Eu²⁺ ions. The enhancement observed in the intensity of Eu²⁺ emission around 420 nm with the addition of TlBr in KCl_0.5Br_0.5:Eu²⁺ powder phosphors is attributed to the energy transfer from Tl⁺ → Eu²⁺ ions. Photostimulated luminescence (PSL) studies of γ‐irradiated KCl_0.5Br_0.5:Eu²⁺, Tl⁺ mixed phosphors are reported and a tentative PSL mechanism in the phosphors has been suggested. Copyright © 2009 John Wiley & Sons, Ltd.