Preparation and photoluminescence properties of the Sr1.56Ba0.4SiO4:0.04Eu2+ phosphor

The Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ phosphors were prepared via a combustion reaction and following the calcination method at low temperature. The influences of the amount of the uncommonly used SrCl₂ flux, different calcination temperatures and time on the structure and the photoluminescence (PL) properties of the phosphors were investigated. Under the excitation of 450 nm blue light, the phosphor shows the intense broad emission band from 490 nm to 650 nm, and the emission peak is centered at 553 nm. The luminescence intensity of Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ was very sensitive to the crystallinity and morphology characteristics of the phosphor. The phosphor calcined at 950 °C for 3 h in 20%H₂/80%Ar atmosphere exhibits improved PL properties due to its high crystallinity and excellent morphology characteristics. The use of the SrCl₂ flux provides a novel way to improve the crystallinity of the silicates phosphors at low preparation temperature.     

Novel EGCG assisted ultrasound synthesis of self-assembled Ca2SiO4:Eu3+ hierarchical superstructures: Photometric characteristics and LED applications

This paper reports for the first time ultrasound, EGCG assisted synthesis of pure and Eu³⁺ (1–5 mol%) activated Ca₂SiO₄ nanophosphors having self-assembled superstructures with high purity. The shape, size and morphology of the product were tuned by controlling influential parameters. It was found that morphology was highly dependent on EGCG concentration, sonication time, pH and sonication power. The probable formation mechanism for various hierarchical superstructures was proposed. The PL studies of Ca₂SiO₄:Eu³⁺ phosphors can be effectively excited by the near ultraviolet (UV) (396 nm) light and exhibited strong red emission around 613 nm, which was attributed to the Eu³⁺ (⁵D₀ → ⁷F₂) transition. The concentration quenching phenomenon was explained based on energy transfer between defect and Eu³⁺ ions, electron–phonon coupling and Eu³⁺–Eu³⁺ interaction. The Judd–Ofelt intensity parameters and radiative properties were estimated by using PL emission spectra. The photometric studies indicate that the obtained phosphors could be a promising red component for possible applications in the field of white light emitting diodes.     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.     

Encapsulating MAl2O4:Eu2+, Dy3+ (M = Sr,Ca, Ba) phosphors with triethanolamine to enhance water resistance

Traditional aluminates phosphors with persistent luminescence are chemically unstable to water or moisture. Thus, how to improve the water-resistance of these phosphors is becoming a key issue in their practical applications. In this work, a series of alkaline earth aluminate phosphors including MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca, Ba) have been prepared by a co-precipitation synthesis and postannealing approach, using 8-hydroxyquinoline and sodium oxalate as precipitants. The samples before and after encapsulation were well characterized by means of XRPD, FESEM, FT-IR, TGA-DTG and PL techniques as well as water resistance measurements. The precipitants involved can react with Al³⁺ and Sr²⁺ (or Ca²⁺, Ba²⁺) to form complex compounds in aqueous solution, which further convert into porous phosphors by postannealing method under reducing atmosphere. Next, triethanolamine encapsulation at room temperature was conducted onto their surfaces to improve the water resistance. The results reveal that the encapsulation of aluminate phosphors with triethanolamine can effectively enhance the water resistance, and minimally affect on persistent phosphorescence.     

The influence of some processing conditions on host crystal structure and phosphorescence properties of SrAl2O4:Eu2+, Dy3+ nanoparticle pigments synthesized by combustion technique

The spectroscopic and host phase properties of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors with a series of different initiating combustion temperature, urea concentration as a fuel and critical pH of precursor solution are investigated. The SrAl₂O₄:Eu²⁺, Dy³⁺ nanoparticle pigments were obtained by exothermic combustion process within less than 5 min. The sample that ignited at initiating combustion temperature of 600 °C exhibits highest intensity emission peak at 517 nm in which the SrAl₂O₄ host phase has the maximum fraction of monoclinic SrAl₂O₄ phase. The excitation spectra consist of 240 and 254 nm broad peaks. The experimental results show that the optimum ratio of urea is 2.5 times higher than theoretical quantities for best emission condition of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphor particles. The critical pH was obtained about 5.2. The crystallite size of these pigments is about 40 nm before thermal treatment and 62 nm after thermal treatment, respectively.     

Effect of Sr2+-doping on structure and luminescence properties of BaAl2Si2O8:Eu2+ phosphors

Sr²⁺ doped BaAl₂Si₂O₈:Eu²⁺ phosphor was synthesized by chemical co-precipitation method. With the increase of Sr²⁺ concentration, the phase structure of (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ changes from hexagonal phase to monoclinic phase owing to large activation energy in SrAl₂Si₂O₈ system. (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ phosphor exhibits a broad blue band peaking at 425 nm due to the 4f⁶5d–4f⁷(⁸S_7/2) transition of Eu²⁺ ions. The emission intensity increases, accompanied by the blue shift of emission maximum from 459 to 417 nm with the Sr²⁺ doping concentration increasing. The optimal concentration of Sr²⁺ ion is 40%, and the phosphor shows high color stability in CIE chromaticity diagram. The result indicates that Sr²⁺ doped phosphor not only can enhance the relative intensity but also can adjust the chromaticity coordinate.     

Effect of Na+ co-dopant and activator concentration on luminescent properties of CaGa4O7:Eu3+

Two series of calcium gallate phosphors: Ca_1?xEu_xGa₄O₇ and Ca_1?2xEu_xNa_xGa₄O₇ (x=0, 0.002, 0.01, 0.02, 0.03, 0.05) were synthesized by a modified Pechini method and their optical properties at 298 and 77 K were investigated. In undoped CaGa₄O₇ upon 255 nm excitation a bluish white emission (λ_max=500 nm) followed by an afterglow of the same color lasting for 10–20 s was observed. Eu³⁺-doping quenched the host-related luminescence and the characteristic red emission of the dopant with maximum at 613 nm appeared. Its excitation spectrum consisted of a broad band assigned to ligand to metal, O^2?→Eu³⁺, charge transfer absorption and narrow lines arising from intraconfigurational transitions within the 4f⁶ states of Eu³⁺ ion. The effects of Eu³⁺ concentration and Na⁺ co-doping on the luminescence properties and decay kinetics were studied. Low temperature emission spectra showed that Eu³⁺ ions are positioned in environments of different symmetries. Their relative populations changed with the activator content. Co-doping with Na⁺ ions led to a remarkable reduction of the number of Eu³⁺ sites as well as to noticeable improvement of the luminescence brightness though it did not affect the decay time of the emission. The quantum efficiencies of singly doped CaGa₄O₇:Eu³⁺ were very low (in the range of 1–3.7%). Na⁺ co-doping improved this parameter leading to the highest efficiency of 11% for CaGa₄O₇:3%Eu³⁺,3%Na⁺.     

Synthesis and photoluminescence properties of YVO4:Eu3+, Al3+ phosphor

The Y_0.95?xAl_xVO₄:5%Eu³⁺ (0≤x≤0.1) phosphors were successfully synthesized by solid state reaction at 900 °C for 6 h, and their luminescence properties were investigated under UV and VUV excitation. Monitoring at 619 nm, a strong broad absorption was enhanced by co-doping of Al³⁺ into the YVO₄:Eu³⁺ lattices at 256 nm under UV excitation. The VUV excitation spectra also showed the enhanced excitation bands at about 156 and 200 nm. Under 254 or 147 nm excitation, it was found that Y_0.95?xAl_xVO₄:Eu³⁺(0≤x≤0.1) phosphors showed strong red emission at about 619 nm corresponding to the electric dipole ⁵D₀^–7F₂ transition of Eu³⁺. The improvement of luminescence intensity of YVO₄:Eu³⁺ was also observed after partial substituting Y³⁺ by Al³⁺ and the optimal luminescence intensity appeared with incorporation of 2.5 mol% Al³⁺.     

Fabrication and luminescence properties of Al2O3:Tb3+ microspheres via a microwave solvothermal route

Al₂O₃:Tb³⁺ green phosphors were synthesized via a microwave solvothermal and thermal decomposition route, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra, and decay curves. XRD results indicate that Tb³⁺ doped samples are γ-Al₂O₃ after being calcined at 773 K. SEM results show that the particles of Al₂O₃:Tb³⁺ are hierarchically nanostructured microspheres assembled from nanosheets. The PL spectra indicate that the ⁵D₄→⁷F₅ (545 nm) electric dipole transition is the most intensive when excited at 235 nm. It is shown that 0.7 mol% of doping concentration of Tb³⁺ ions in γ-Al₂O₃:Tb³⁺ is optimum. According to Dexter's theory, the critical distance between Tb³⁺ ions for energy transfer was determined to be 18.4 Å. It is found that the curve followed the single-exponential decay. The excellent chromaticity coordinates of Al₂O₃:Tb³⁺ phosphors, as defined by the International Commission on Illumination (CIE), indicate that it is a good candidate for use in light display systems and optoelectronic devices.     

Photoluminescence properties of Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors

Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors, Ca_0.736?ySi_9.6Al_2.4O_0.8N_15.2:0.064 Eu²⁺, yMn²⁺, were firstly synthesized by the high temperature solid state reaction method. The effects of doped Eu²⁺ and Eu²⁺–Mn²⁺ concentrations on the photoluminescence properties of the as-prepared phosphors were investigated systematically. Powder X-ray diffraction shows that pure Ca-α-SiAlON phase is synthesized after sintering at 1700 °C for 2 h under 0.5 MPa N₂ atmosphere. The excitation spectra of Eu²⁺-doped Ca-α-SiAlON phosphors are characterized by two dominant bands centered at 286 nm and 395 nm, respectively. The photoluminescent spectrum of Eu²⁺-doped Ca-α-SiAlON phosphor exhibits an intense emission band centered at 580 nm due to the allowed 4f ⁶5d→4f ⁷ transition of Eu²⁺, showing that the phosphor is a good candidate for creating white light when coupled to a blue LED chip. The intensities of both excitation and emission spectra monotonously decrease with the increment of codoped Mn²⁺ content (i.e. y value), indicating that energy transfer between Eu²⁺ and Mn²⁺ is inefficient in the case of Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors.     

Blue emission in Eu2+ activated MgXAl10O17 (X = Sr,Ca) phosphors

Here we reported photoluminescence properties of Eu²⁺ activated in novel and existing MgXAl₁₀O₁₇ (X = Sr, Ca) phosphor which has been prepared by combustion synthesis at 550 °C under UV and near UV excitation wavelength. The PL emission properties of MgSrAl₁₀O₁₇:Eu²⁺ were monitored at 254 nm and 354 nm respectively keeping emission wavelength at 469 nm. Whereas novel MgCaAl₁₀O₁₇:Eu²⁺ exhibit emission band at 452 nm keeping excitation at 378 nm. These blue emission corresponds to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. Further phosphor was analyzed by XRD for the confirmation of desired phase and purity.     

Probing lattice defects in Sr2MgSi2O7:Eu2+,Dy3+

The Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ materials were prepared with a solid state reaction and their microscopic structure (at 295 K only) and luminescence were studied at selected temperatures between 150 and 295 K. Undisturbed Sr crystal planes were common in the TEM images of the undoped Sr₂MgSi₂O₇ material, whereas with Eu²⁺ doping more disturbed planes were observed even in the nanometer scale. With Dy³⁺ co-doping, a large number of small lattice domains created by the discontinuities in the crystal structure was observed. The domains with different orientations seem to be centered around point defects. The decay curves of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ showed fast (ms scale) persistent luminescence. The intensity of persistent luminescence increased considerably between 200 and 250 K while remaining constant in the ranges of 150–200 and 250–295 K. The changes were used to study the depth of the traps. In general, Dy³⁺ co-doping was found to deepen the traps.     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

A potential red emitting K4Ca(PO4)2: Eu3+ phosphor for white light emitting diodes

Europium (III) ions doped red phosphors K₄Ca(PO₄)₂ were prepared first time by high temperature solid state reaction method. The prepared phosphors structure was examined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The thermal properties of the synthesized phosphor were investigated by differential scanning calorimetry (DSC) analysis. Photoluminescence (PL) spectra of K₄Ca(PO₄)₂:Eu³⁺ phosphors have shown strong red emission at 618 nm (⁵D₀→⁷F₂) with near UV an excitation wavelength of λ_exc=394 nm (⁷F₀→⁵L₆). In addition, the decay curves and CIE color coordinate measurements are also carried out. Hence, emission and excitation characterization of synthesized phosphors shows that the phosphors may be a promising red component for the application in the white light emitting diodes (WLEDs).     

The influence of Eu3+ doping on photoluminescent properties of red emitting phosphor YInGe2O7:Eu3+ by microwave assisted and conventional sintering method

This paper describes an investigation of the crystalline morphology and photoluminescent properties of YInGe₂O₇ powders doped with different Eu³⁺ concentrations using microwave assisted sintering and conventional sintering. X-ray powder diffraction analysis confirmed the formation of monoclinic YInGe₂O₇ structure as YInGe₂O₇:Eu³⁺ powders were sintered at 1200 °C in microwave furnace for 1 h, and the raw material phase of Y₂O₃ was observed when Eu³⁺ concentration was below 30 mol%. Scanning electron microscopy showed microwave assisted sintering results in smaller particle size and more uniform grain size distribution. In the photoluminescent (PL) studies, the concentration quenching effect was observed under the excitation at 393 nm, but not under the excitation at CTS band. The ⁵D₀→⁷F₂ transition (620 nm), exhibits a non-exponential decay behavior as YInGe₂O₇:Eu³⁺ powders were sintered by microwave with the Eu³⁺ concentration higher than 50 mol%.     

5D0→7F1 and 5D0→7F2 transition in europium doped halosulphates for mercury-free lamps

Polycrystalline Na₃SO₄F:Eu and NaMgSO₄F:Eu halosulphate phosphors prepared by a wet chemical method have been studied for its photoluminescence (PL) and thermoluminescence (TL) characteristics. Two well resolved peaks are observed at 593 nm and 614 nm, which are assigned to due to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions of Eu³⁺ ions. TL is observed at temperatures between 100 °C and 300 °C. In this paper, we report PL emission spectra of Eu³⁺ and TL glow curves, which are more sensitive than the standard TLD-CaSO₄:Dy. The presented phosphors are applicable for the mercury free lamps and solid state lighting devices.     

Synthesis and photoluminescent behavior of Eu3+-doped alkaline-earth tungstates

Eu³⁺-doped alkaline-earth tungstates MWO₄ (M=Ca²⁺, Sr²⁺, Ba²⁺) were prepared by a polymeric precursor method based on the Pechini process. The polymeric precursors were calcined at 700 °C for 2 h in order to obtain well-crystallized powders and then characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and photoluminescence spectroscopy (PL). All prepared samples showed a pure crystalline phase with scheelite-type structure confirmed by XRD. It was noted that the charge-transfer band shifted from 260 to 283 nm when calcium is replaced by strontium. However, this band was not observed for Eu³⁺-doped barium tungstate. Upon excitation at 260 nm, the emission spectra are dominated by the red ⁵D₀→⁷F₂ transition at 618 nm. By analyzing of the emission lines, it was inferred that Eu³⁺ ions occupy low symmetry sites in the host lattice. It was also found that Eu³⁺-doped SrWO₄ displays better chromaticity coordinates and greater luminescence intensity than the other samples.     

Synthesis and characterization of fast-decaying bluish green phosphors of Tb3+-doped CaSi2O2N2 for 2D/3D plasma display panels

Oxynitride phosphor powders comprising of CaSi₂O₂N₂ doped with Tb³⁺ were successfully synthesized using a high-temperature solid-state reaction method. The experimentally determined photoluminescence (PL) properties of the produced phosphors meet the requirements of 2D/3D plasma display panels (PDPs). In particular, under the excitation of vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation, emission peaks corresponding to the ⁵D₃→⁷F_J (J=6, 5, 4, 3) and ⁵D₄→⁷F_J (J=6, 5, 4, 3) transitions of Tb³⁺ ions were recorded. Monitoring the ⁵D₄→⁷F₅ emission of Tb³⁺ at 545 nm, the excitation bands were assigned to the host-related absorption as well as the 4f–5d (fd) and the 4f–4f (ff) transitions of Tb³⁺. The produced phosphors can be efficiently excited at 147 nm, and have an adequately short decay time (τ_1/10=1.14 ms).     

White-light generation through Ce3+/Mn2+-codoped and Eu2+-doped Ba1.2Ca0.8SiO4 T-phase phosphors

Hexagonal Ba_1.20Ca_0.8?2x?ySiO₄:xCe³⁺,xLi⁺,yMn²⁺ phosphors exhibit two emission bands peaking near 400 and 600 nm from the allowed f–d transition of Ce³⁺ ions and the forbidden ⁴T₁–⁶A₁ transition of Mn²⁺ ions, respectively. The strong interaction between Ce³⁺/Mn²⁺ ions is investigated in terms of energy transfer, crystal field effect, and microstructure by varying their concentrations. They show a higher quenching temperature of 250 °C than that of a commercially used (Ba,Sr)₂SiO₄:Eu²⁺ phosphor (150 °C). Finally, mixtures of these phosphors with green-emissive Ba_1.20Ca_0.70SiO₄:0.10Eu²⁺ are tested and yielded correlated color temperatures from 3500 to 7000 K, and color rendering indices up to 95%.