A potential green-emitting phosphor Ca8Mg(SiO4)4Cl2:Eu for white light emitting diodes prepared by sol-gel method

A potential green emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺ was prepared by modified sol-gel method. The factors those affect the photoluminescence intensity including heating temperature, the usage of the chlorine source CaCl₂ and the concentration of dopant Eu²⁺ were also investigated in detail. As comparison, the phosphor prepared by solid-state reaction was also prepared. The phosphors show intense absorption in the range of 375-450 nm, which makes it a potential candidate of green emitting phosphor used for near-UV or blue light excited white LEDs.     

Photoluminescence studies of red-emitting NaEu(WO4)2 as a near-UV or blue convertible phosphor

Sodium europium double tungstate [NaEu(WO₄)₂] phosphor was prepared by the solid-state reaction method. Its crystal structure, photoluminescence properties and thermal quenching characteristics were investigated aiming at the potential application in the field of white light-emitting diodes (LEDs). The influences of Sm doping on the photoluminescence properties of this phosphor were also studied. It is found that this phosphor can be effectively excited by 394 or 464 nm light, which nicely match the output wavelengths of near-ultraviolet (UV) or blue LED chips. Under 394 or 464 nm light excitation, this phosphor exhibits stronger emission intensity than the Y₂O₂S:Eu³⁺ or Eu²⁺-activated sulfide phosphor. The introduction of Sm³⁺ ions can broaden the excitation peaks at 394 and 464 nm of the NaEu(WO₄)₂ phosphor and significantly enhance its relative luminance under 400 and 460 nm LEDs excitation. Furthermore, the relative luminance of NaEu(WO₄)₂ phosphor shows a superior thermal stability compared with the commercially used sulfide or oxysulfide phosphor, and make it a promising red phosphor for solid-state lighting devices based on near-UV or blue LED chips.     

Green Eu-doped Ba3Si6O12N2 phosphor for white light-emitting diodes: Synthesis, characterization and theoretical simulation

The Eu²⁺-doped Ba₃Si₆O₁₂N₂ green phosphor (Eu_xBa_3−xSi₆O₁₂N₂) was synthesized by a conventional solid state reaction method. It could be efficiently excited by UV-blue light (250-470 nm) and shows a single intense broadband emission (480-580 nm). The phosphor has a concentration quenching effect at x=0.20 and a systematic red-shift in emission wavelength with increasing Eu²⁺ concentration. High quantum efficiency and suitable excitation range make it match well with the emission of near-UV LEDs or blue LEDs. First-principles calculations indicate that Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor exhibits a direct band gap, and low band energy dispersion, leading to a high luminescence intensity. The origin of the experimental absorption peaks is clearly identified based on the analysis of the density of states (DOS) and absorption spectra. The photoluminescence properties are related to the transition between 4f levels of Eu and 5d levels of both Eu and Ba atoms. The 5d energy level of Ba plays an important role in the photoluminescence of Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor. The high quantum efficiency and long-wavelength excitation are mainly attributed to the existence of Ba atoms. Our results give a new explanation of photoluminescence properties and could direct future designation of novel phosphors for white light LED.     

KBaPO4:Ln (Ln=Eu, Tb, Sm) phosphors for UV excitable white light-emitting diodes

This letter reports the novel three emission bands based on phosphate host matrix, KBaPO₄ doped with Eu²⁺, Tb³⁺, and Sm³⁺ for white light-emitting diodes (LEDs). The phosphors were synthesized by solid-state reaction and thermal stability was elucidated by measuring photoluminescence at higher temperatures. Eu²⁺-doped KBaPO₄ phosphor emits blue luminescence with a peak wavelength at 420 nm under maximum near-ultraviolet excitation of 360 nm. Tb³⁺-doped KBaPO₄ phosphor emits green luminescence with a peak wavelength at 540 nm under maximum near-ultraviolet excitation of 370 nm. Sm³⁺-doped KBaPO₄ phosphor emits orange-red luminescence with a peak wavelength at 594 nm under maximum near-ultraviolet excitation of 400 nm. The thermal stabilities of KBaPO₄:Ln (Ln=Eu²⁺, Tb³⁺, Sm³⁺), in comparison to commercially available YAG:Ce³⁺ phosphor were found to be higher in a wide temperature range of 25-300 °C.     

Preparation and luminescence of blue-emitting phosphor Ca2PO4Cl:Eu2+ for n-UV white LEDs

A series of blue-emitting Ca_2 ? xEu_xPO₄Cl phosphors were synthesized by a solid state method in a reducing atmosphere. The factors those affect the structure and the photoluminescence (PL) intensities of phosphors, including the dosage of chlorine source CaCl₂, reaction time and annealing temperature, have been investigated in detail. X-ray diffraction (XRD) and photoluminescence measurements were performed to testify the crystal structure and luminescent properties. The optimal Eu²⁺ concentration was determined, and the mechanism of the concentration quenching was predominated by dipole–dipole interaction. The present phosphor exhibits a strong absorption in the near-UV region, emits an intense blue emission centered at 451 nm and presents excellent thermal stability, suggesting that the phosphor is competitive as a promising blue-emitting phosphor for near ultraviolet (n-UV) light-emitting diodes (LEDs).     

Intense green-emitting Sr2LiSiO4F:Eu2+ phosphor for n-UV white LEDs

Eu²⁺-activated Sr₂LiSiO₄F phosphors were synthesized at 900°C by solid-state reaction in reducing atmosphere, and their photoluminescence (PL) properties were systematically investigated by diffuse reflection spectra, PL excitation and emission spectra, and by the fluorescence decay curve. Sr₂LiSiO₄F:Eu²⁺ emits intense green light at 520 nm originating from the 5d¹4f⁶−4f⁷ transition of Eu²⁺ under 365 nm n-UV excitation. The PL excitation spectrum matches the emission from n-UV chips. These materials could be promising green phosphors for use in generating white light in phosphor-converted white light-emitting-diodes (LEDs).     

Sm-activated gadolinium molybdate: an intense red-emitting phosphor for solid-state lighting based on InGaN LEDs

Sm³⁺-activated gadolinium molybdate, Gd₂(MoO₄)₃:Sm³⁺ red-emitting phosphor was prepared by conventional solid-state method. The structure, morphology, and luminescent properties of these powder samples have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescent spectrophotometry, respectively. The as-obtained phosphor has a monoclinic structure with single crystalline phase. Its mean particle size is about 6-8 μm with pseudo-pompon shape and large surface area, which is suitable for manufacture of white LEDs. The phosphor can be efficiently excited by incident light of 348-445 nm, well matched with the output wavelength of a near-UV InGaN-based chip, and re-emits an intense red light peaking at 650 nm. By combing this phosphor with a 405 nm-emitting InGaN chip, a red LED was fabricated, so that the applicability of this novel phosphor to white LEDs was confirmed. It is considered to be an efficient red-emitting conversion phosphor for solid-state lighting based on InGaN LEDs.     

Sr9R2−xEuxW4O24 (R=Gd and Y) red phosphor for near-UV and blue InGaN-based white LEDs

Eu³⁺-activated phosphors, Sr₉R_2?xEu_xW₄O₂₄ (R=Gd and Y ), were prepared by the conventional solid-state reaction method and their photoluminescent properties were studied. The phosphors show intense red emission under 395 and 465 nm light excitation, which is matched with the light-emitting wavelength of a near-UV-emitting and a blue-emitting InGaN chips, respectively. Bright red-light-emitting diodes (LEDs) and white-light-emitting diodes (WLEDs) were fabricated by coating Sr₉Y _0.4Eu_1.6W₄O₂₄ phosphor onto ～395 nm-emitting InGaN chips and ～460 nm blue-emitting InGaN chips, respectively. The good performances of the LEDs demonstrate that the tungstates are suitable for application of near-UV and blue InGaN-based WLEDs.     

Novel green-emitting Na2CaPO4F:Eu phosphors for near-ultraviolet white light-emitting diodes

In this study, green-emitting Na₂CaPO₄F:Eu²⁺ phosphors were synthesized by solid-state reactions. The excitation spectra of the phosphors showed a broad hump between 250 and 450 nm; the spectra match well with the near-ultraviolet (NUV) emission spectra of light-emitting diodes (LEDs). The emission spectrum showed an intense broad emission band centered at 506 nm. White LEDs were fabricated by integrating a 390 nm NUV chip comprising blue-emitting BaMgAl₁₀O₁₇:Eu²⁺, green-emitting Na₂CaPO₄F:0.02 Eu²⁺, and red-emitting CaAlSiN₃:Eu²⁺ phosphors into a single package; the white LEDs exhibited white light with a correlated color temperature of 5540 K, a color-rendering index of 90.75, and color coordinates (0.332, 0.365) close to those of ideal white light.     

Intense green/yellow emission in Ca8Zn(SiO4)4Cl2:Eu, Mn through energy transfer for blue-LED lighting

Eu²⁺ and Mn²⁺ co-doped Ca₈Zn(SiO₄)₄Cl₂ phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu²⁺ to Mn²⁺ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu²⁺ and a yellow band at 550 nm of Mn²⁺. The excitation spectra corresponding to 4f⁷-4f⁶5d transition of Eu²⁺ cover the spectral range of 370-470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu²⁺ followed by simultaneous increase of fluorescent intensity of Mn²⁺ with increasing Mn²⁺ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu²⁺ and Mn²⁺ co-doped Ca₈Mg(SiO₄)₄Cl₂ and Ca₃SiO₄Cl₂, demonstrating a potential application in phosphor converted white LEDs.     

A red oxide phosphor, Sr2ScAlO5:Eu2+ with perovskite-type structure, for white light-emitting diodes

Sr2ScAlO5:Eu2+,a red oxide phosphor with a perovskite-type structure,has been synthesized through a solid-state reaction and its luminescence properties have been investigated.An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra,indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes.A broad red emission band at 620 nm is found from the emission spectra,originating from the 4f 6 5d-4f 7 transition of the Eu 2+ ions.The best doping content of Eu in this material is about 5%.Sr2ScAlO5:Eu2+is a highly promising red phosphor for use in white light-emitting diodes.     

Orange emissive Sr3Al2O5Cl2:Eu2+ phosphor for warm-white light-emitting diodes

Orange-emitting Sr₃Al₂O₅Cl₂:Eu²⁺ phosphors were synthesized by a high-temperature solid-state reaction. The excitation spectrum shows a broad band from the UV region to the blue region. The emission spectrum shows strong orange emission peaking at 610 nm, attributed to the d–f transition of the Eu²⁺ ion. By combining the Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor with 420 nm and 460 nm chips, three white light-emitting diodes (LEDs) were fabricated. The warm-white LEDs show color rendering indexes of 76, 66 and 90 with color temperatures of 2447, 3546 and 4300 K, respectively. This new phosphor exhibits the potential to act as a single host doped with Eu²⁺ phosphor for UV or blue chip excited white LEDs.     

Thermally stable luminescence of blue LiSrPO4:Eu2+ phosphor for near-UV light-emitting diodes

Blue phosphor, LiSrPO₄:Eu²⁺, was prepared by solid-state reaction method under a weak reductive atmosphere and investigated by means of photoluminescence, concentration quenching process, and temperature dependence of luminescence. These results show that LiSrPO₄:Eu²⁺ can be efficiently excited by the UV-visible light of 250–440 nm and exhibits bright blue emission. Furthermore, Eu²⁺-doped LiSrPO₄ phosphor shows high thermally stable luminescence comparable to commercial phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM). Two bright blue LEDs were fabricated by incorporating an InGaN-based near-UV chip with the obtained phosphor LiSrPO₄:Eu²⁺ and BAM, respectively. Their luminescence properties were compared based on different forward-bias currents. All the characteristics suggest that LiSrPO₄:Eu²⁺ is a good blue phosphor candidate for creating white light in phosphor-conversion white LEDs.     

Synthesis and luminescence properties of Na2Ba2Si2O7:Eu2+ phosphor

Green-emitting phosphor Na₂Ba₂Si₂O₇:Eu²⁺ has been synthesized by a conventional high-temperature solid-state reaction. The phase structure and luminescence properties are characterized by the X-ray powder diffraction, diffuse reflectance spectra, photoluminescence excitation and emission spectra, temperature-dependent emission spectra, respectively. It can be efficiently excited in the wavelength range of 325–400 nm and consists of a strong broad green band centered at about 501 nm, which is ascribed to 4f⁶6s⁰5d¹ → 4f⁷6s²5d⁰ transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in the Na₂Ba₂Si₂O₇ host is about 0.8 mol % and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, and the activation energy for thermal quenching is calculated as 0.34 eV.     

Photoluminescence properties of nanocrystalline La2TeO6:Eu phosphor prepared by Pechini sol-gel method

La₂TeO₆:Eu³⁺ nanophosphors were prepared by Pechini sol-gel process, using lanthanide nitrates and telluric acid as precursor. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TG), photoluminescence spectra (PL) and fluorescence lifetime were used to characterize the resulting phosphors. The results of XRD indicate that all samples crystallized completely at 1023 K and are isostructural with the orthorhombic La₂TeO₆. SEM study reveals that the samples have a strong tendency to form agglomerates with an average size ranging from 50 to 80 nm. The photoluminescence intensity and chromaticity were improved for excitation at 254 and 395 nm. The optimized phosphor La_1.80Eu_0.10TeO₆ could be considered as an efficient red-emitting phosphor for solid-state lighting devices based on GaN LEDs.     

Optical study of rare earth activated NaBa0.45Sr0.55PO4 phosphor

Dy³⁺ and Eu²⁺ activated triple phosphate NaBa_0.45Sr_0.55PO₄ phosphors were prepared by facile combustion synthesis. Excellent emission observed when NaBa_0.45Sr_0.55PO₄:Dy³⁺ and NaBa_0.45Sr_0.55PO₄:Eu²⁺ excited at 348 nm and 354 nm wavelength respectively. From a powder X-ray diffraction (XRD) analysis, the formation of compound with a trigonal–hexagonal scalenohedral structure was confirmed. In the photoluminescence spectra, the NaBa_0.45Sr_0.55PO₄:Dy³⁺ phosphor emits two distinctive colours: a blue band centred at 482 nm and a yellow band at 576 nm originating from Dy³⁺ whereas NaBa_0.45Sr_0.55PO₄:Eu²⁺ emits blue colour at 470 nm. Also, surface morphology has been studied by scanning electron microscope (SEM). Phosphors exhibit a strong absorption in the range of 340–400 nm and chromatic properties indicated that present phosphor is a hopeful candidate for near ultra violet light emitting diodes (nUV LEDs).     

Synthesis and luminescent properties of a new red-emitting phosphor for solid-state lighting: Eu0.1GdxLa1.9−xTeO6 (0.02?x?0.1)

The photoluminescence (PL) emission and excitation behavior of red-emitting Eu_0.1Gd_xLa_1.9−xTeO₆ (0.02?x?0.1) powder phosphors is reported. Three dominant bands centered at 395, 466 and 534 nm characterized the excitation spectrum. Under the excitation of 395 nm UV light, the emission spectrum exhibits an intense peak centered at 616 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺. Because the f→f transitions are located in the wavelength range of blue or near-UV range, optimized phosphor, Eu_0.10Gd_0.08La_1.82TeO₆, is a promising material for solid-state lighting based on GaN LEDs applications.     

Study of photophysical properties AlBaq5

Pure and Ba²⁺ doped Alq₃ complexes were synthesized by simple precipitation method at room temperature, maintaining stoichiometric ratio. These complexes were characterized by XRD, UV–vis and FT-IR and photoluminescence (PL) spectra. XRD analysis reveals the polycrystalline nature of the synthesized complexes, while UV and FTIR confirm the molecular structure and the completion of quinoline ring formation and presence of quinoline structure in the metal complex. PL spectra of Alq₃ compared with barium doped complexes exhibit highest intensity in comparison to Alq₃ phosphor, which proves that barium enhances PL emission intensity of Alq₃ phosphor. The excitation spectra of the synthesized complexes are in the range of 300–480 nm with a broad peak in the range of 429–440 nm and shoulder at 380 nm, but with varying intensity. The emission wavelength lies in the range of 501–506 nm. Among all the synthesized complexes, AlBa₂q₅ exhibits maximum emission intensity. These remarkable properties of AlBaq₅ could be considered as promising materials as optoelectronic materials as well as green light emissive materials for OLEDs, PLLCD and solid state lighting applications.     

Resonance Excitation of Photoluminescence in Crystalline Uranyl Acetate Dihydrate

A method for rapid identification of uranyl compounds based on resonance fiber-optic photoluminescence (PL) excitation by ultraviolet-laser or LED radiation is proposed. This method was used to measure the PL spectra of an extremely small volume (10^–9 cm³) of crystalline uranyl acetate dehydrate UO₂(CH₃COO)₂ ? 2H₂O with an exposure of 10^–3 s. Semiconductor LEDs with wavelengths of 369, 385, 410, and 466 nm and a repetitively pulsed nitrogen laser with a lasing wavelength of 337 nm served as sources of excitation radiation. The operating range of a small-sized minispectrometer used in these experiments was 200–1000 nm.     

Luminescence studies of rare earth doped yttrium gadolinium mixed oxide phosphor

This paper reports the photoluminescence and thermoluminescence properties of gamma ray induced rare earth doped yttrium gadolinium mixed oxide phosphor. The europium (Eu³⁺) was used as rare earth dopant. The phosphor was prepared by chemical co-precipitation method according to the formula (Y_2−x−yGd_x) O₃: Eu_y³⁺ (x=0.5; y=0.05). The photoluminescence emission spectrum of the prepared phosphor shows intense peaks in the red region at 615 nm for ⁵D₀→⁷F₂ transitions and the photoluminescence excitation spectra show a broad band located around 220–270 nm for the emission wavelength fixed at 615 nm. The thermoluminescence studies were carried out after irradiating the phosphor by gamma rays in the dose range from 100 Gy to 1 KGy. In the thermoluminescence glow curves, one single peak was observed at about 300 °C of which the intensity increases linearly in the studied dose range of gamma rays. The glow peak was deconvoluted by GlowFit program and the kinetic parameters associated with the deconvoluted peaks were calculated. The kinetic parameters were also calculated by various glow curve shape and heating rate methods.