Phase Phosphor Research Articles

One pot auto-ignition based synthesis of novel Sr2CeO4: Ho3+ nanophosphor for photoluminescent applications

Ho3+ (0.25–7 mol%) doped Sr2CeO4 nanophosphors were synthesized by solution combustion method using urea as fuel. The structural properties of the nanophosphors were investigated by powder X-ray diffraction studies (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. UV–Visible and photoluminescence (PL) spectroscopic techniques were used for analysing the optical properties of the nanoparticles. PXRD and TEM results revealed the formation of Sr2CeO4: Ho3+ nanocrystalline particles with orthorhombic crystal structure. From the UV–Vis studies the optical band gap energy found to decrease from 5.9 to 5.74 eV with increase in dopant concentration. The PL spectra exhibit the broad excitation band from 200 to 400 nm which concurs well with the commercial near UV LED. The PL spectra vary with the dopant content due to energy transfer from the host to the activator. In this present work we demonstrate that color tuning of phosphor can be achieved by merely varying the Ho3+ ions concentration. The CIE and CCT chromaticity coordinates suggests Sr2CeO4: Ho3+ nanophosphors may be potentially applicable as promising single – phased phosphors for lighting applications.

Effect of ultrasound treatment on the morpho-structural and luminescent characteristics of cerium doped yttrium silicate phosphors

Cerium activated yttrium silicate (Y2SiO5:Ce) phosphors were prepared by gel-combustion, using yttrium–cerium nitrate as oxidizer, aspartic acid as fuel and TEOS as source of silicon. Two modalities for samples preparation were approached namely: the classical gel-combustion and sonication gel-combustion. The ultrasound treatment during the gelling stage has a positive effect on the structural and luminescent characteristics of the final product. Therefore, a well crystallized single X2–Y2SiO5 phase phosphor was obtained at 1200°C. Based on FT-IR and XRD investigations, conversion of X1 to X2–Y2SiO5 phases is observed as the firing temperature is varied (1100°C, 1200°C, 1300°C 1400°C). The ultrasound treatment leads to smaller particle size and enhances the luminescent performances up to 151% in comparison with samples prepared by classical way.

The crystal structure and luminescence of phosphor Ba9Sc2Si6O24:Eu2+,Mn2+ for white light emitting diode

Single-phase white light emitting phosphor Ba9Sc2Si6O24:Eu2+,Mn2+ has been successfully prepared by solid-state reaction. The energy transfer process from Eu2+ to Mn2+ has been demonstrated based on the excitation spectra, luminescent lifetime and low temperature spectra. Under ultraviolet light excitation, Eu2+ emits blue light (∼460nm) and green light (∼512nm), Mn2+ gets the energy transferred from Eu2+ and emits red light (∼615nm). White light is obtained by tuning the concentration of Eu2+ and Mn2+. Those results suggest that Ba9Sc2Si6O24:Eu2+,Mn2+ can be a promising single phase phosphor for white light emitting diode (w-LED).

Photoluminescence properties of Na(Sr,Ca)VO4:Eu(3+) phosphors.

Eu(3+)-activated novel alkaline earth metal (Sr and Ca) vanadate phosphors, Na(Sr(0.97-x), Ca(x))VO4:Eu0.03(3+) (x = 0 to 0.97) has been successfully synthesized using solid state reaction method and characterized by XRD, XPS, FE-SEM, luminescence (PLE, PL and CIE coordinate) and decay rate measurements as a function of Ca ion concentration. Phosphors show a broad excitation band (monitored for (5)D0 --> (7)F2 transition of Eu(3+)) in the 230-430 nm wavelength regions which make them highly suitable for LED chips. Material gives strong emission of Eu(3+) ion (λex = 323 nm) and intensity of this emission increases with increase in the doping concentration of Ca ions until a maximum is reached for Na(Sr0.22, Ca0.75)VO4:Eu0.03(3+) (x = 0.75) phase phosphor. The intensity ratio of (5)D0 --> (7)F2 to (5)D0 --> (7)F1 transition (monochromaticity, R) suggest that local symmetry around the Eu(3+) ion increases with increase in Ca ion concentration, which is responsible for enhanced emission.

Study on low temperature solution combustion synthesized Sr2SiO4:Dy3+ nano phosphor for white LED

A series of Dy3+ (1–5mol.%) activated Sr2SiO4 nanophosphors were prepared by low temperature solution combustion method using oxalyl dihydrazide (ODH) as a fuel. The obtained phosphor was well characterized by powder X-ray diffraction, scanning electron microscopy, and UV–visible spectroscopy. The average crystallite sizes were estimated by Debye–Scherrer formula and Williamson–Hall plots and found to be in the range 20–32nm. Energy band gap was found to be widened with increase of Dy3+ ion dopant. Photoluminescence spectra consist of three main groups of peaks in 460–500nm (blue), 555–610nm (yellow) and 677nm (red) respectively. These peaks were assigned to transition of 4F9/2→6H15/2,13/2,11/2. The critical distance between Dy3+ ions and quenching site was found to be ∼16.71Ǻ. The chromaticity co-ordinates of all the prepared phosphors were located in white light; as a result Dy3+ activated Sr2SiO4 is a promising single phased phosphor for white light emitting diodes. Thermoluminescence (TL) of Dy3+ doped Sr2SiO4 nanophosphors were investigated using γ-irradiation in the dose range 1–6kGy at a warming rate of 2.5°Cs−1. The phosphors show a well resolved single glow peak at ∼145°C. The kinetic parameters were estimated by different methods and the results discussed. The TL intensity increases linearly with γ-dose at room temperature. The effect of fading with storage time was found to be ∼66% which is highly useful in radiation dosimetry.

Tunable white-light emission in single-phase Ca_9Gd(VO_4)_7:Tm^3+, Eu^3+

A series of Tm3+ and/or Eu3+ doped Ca9Gd(VO4)7 single composition phosphors were synthesized by a solid state reaction method, and their luminescence properties were investigated. Tm3+ and Eu3+ co-doped Ca9Gd(VO4)7 phosphors showed a blue with the peak at 477 nm and red with the stronger peak at 620 nm dual emission bands under the UV excitation, which originates from the f-f transitions of Tm3+ and Eu3+ ions, respectively. The energy transfer from O2--V5+ CT (charge transfer) energy to Tm3+ and Eu3+ ions as well as the energy transfer from Tm3+ to Eu3+ ions were investigated. The photoluminescence intensity ratio of blue and red emission could be tuned by adjusting the concentration of Tm3+ and Eu3+ ions and as a result the emission color varies from blue to white to red. The white-light emission is realized in single phased phosphor of Ca9Gd(VO4)7:Tm3+, Eu3+ by combining the Tm3+-emission and the Eu3+-emission.

Potential single phased full colour white light Sr2−xCeO4∶xSm3+ phosphor for UV light emitting diodes

A potential single phased white Sr2CeO4∶Sm3+ phosphor was fabricated by a hydrothermal calcine method. The luminescence intensity of Sr2CeO4 host and redistribution depended on the doped Sm3+ concentration. It is also found that the photoluminescence spectrum exhibits a redshift when the Sm3+ concentration is increased from 0 to 2 mol-%. The phosphor can emit full colour white light with the Sm3+ concentration increasing from 0·5 to 1·0 mol-%. The energy transfer model is interpreted as the possible mechanisms of energy transfer from Sr2CeO4 host to Sm3+ in Sr2CeO4∶Sm3+ system. The fabrication and packaging of a white phosphor-converted light emitting diode (LED) by adopting a white Sr2CeO4∶Sm3+ phosphor with an ultraviolet (UV) LED chip with the wavelength of 350 nm is also successfully demonstrated. A white light with colour coordinates (0·3315, 0·3109) and luminescence efficiency of 56 lm W−1 could be obtained from the fabricated LEDs when keeping the Sr2−xCeO4∶xSm3+ phosphor doped with the content of Sm3+ at 1·0 mol-%, which shows that the phosphor is a promising single phase phosphor for UV LED.

Full-color emission generation from single phased phosphor Sr_10[(PO_4)_55(BO_4)_05](BO_2): Ce^3+, Mn^2+, Tb^3+ for white light emitting diodes

A single-phase full-color emitting Sr10[(PO4)5.5(BO4)0.5](BO2): Ce3+, Mn2+, Tb3+ phosphor was synthesized by solid-state reaction for the first time. The characteristic luminescence property of Ce3+ is investigated by Gauss fitting. Energy transfer from Ce3+ to Mn2+ and Ce3+ to Tb3+ in Sr10[(PO4)5.5(BO4)0.5](BO2) is detailedly studied by luminescence spectra, energy-transfer efficiency and lifetimes. Through effective energy transfer, the wavelength-tunable warm white light can be realized with superior chromaticity coordinates of (0.35, 0.32), high color rendering index (Ra = 89) and low correlated color temperature (CCT = 4373K) by coupling the emission bands centered at 441, 542 and 649 nm attributed to the contribution from Ce3+, Mn2+ and Tb3+, respectively. The results indicate the white Sr10[(PO4)5.5(BO4)0.5](BO2):Ce3+, Mn2+, Tb3+ phosphor can serve as a promising candidate for phosphor-converted white-light UV-LEDs.

Effect of strontium and phosphorus source on the structure, morphology and luminescence of Sr 5 (PO 4 ) 2 SiO 4 :Eu 2+ phosphor prepared by solid-state reaction

Sr5(PO4)2SiO4:Eu2+ phosphosilicate phosphor was prepared by high temperature solid-state reaction. Effects of strontium sources (strontium oxide, strontium nitrate and strontium carbonate) and of phosphorus sources (diammonium phosphate, strontium monophosphate) on the reactivity of their mixture during heating and on phase composition, morphology and photoluminescence excitation and emission properties of the phosphors were investigated by TG–DTG–DSC, XRD, SEM and photoluminescence spectroscopy. The sequence of the solid-state reactions when using the different starting reagents was discussed based on the TG–DTG–DSC results. It was found that it is hard to prepare pure Sr5(PO4)2SiO4:Eu2+ phosphor with either of strontium sources studied when stoichiometric (NH4)2HPO4 was used as a phosphorus source. Minor Sr2SiO4 impurity phase was present in the phosphors. The content of impurity phase, the morphology and resultant photoluminescence properties of the phosphors were markedly influenced by the strontium source employed. When SrCO3 was used as the strontium source, the phase purity of the phosphor was improved with the addition of excess (NH4)2HPO4. When (NH4)2HPO4with 5% excess or SrHPO4 in stoichiometric ratio was used as the phosphorus source a pure phase phosphor was obtained. In addition, the morphology and photoluminescence of the phosphor were also influenced by phosphorus source. The possible reasons causing different properties of the phosphors prepared using different raw materials were discussed based on reaction schemes.

Warm white light generation from a single phased phosphor Sr10[(PO4)5.5(BO4)0.5](BO2):Eu2+, Mn2+, Tb3+ for light emitting diodes

A novel single phased white light emitting phosphor Sr10[(PO4)5.5(BO4)0.5](BO2):Eu2+, Mn2+, Tb3+ was synthesized by solid-state reaction for the first time. The crystal structure, photoluminescence properties and the efficient energy transfer from different Eu2+ sites to Mn2+ and Tb3+ in Sr10[(PO4)5.5(BO4)0.5](BO2) is studied in detail by X-ray diffractometry Rietveld method, luminescence spectra, energy-transfer efficiency and lifetimes. Through effective energy transfer, the wavelength-tunable warm white light can be realized with superior chromaticity coordinates of (0.37, 0.30) and low correlated color temperature (CCT = 3512 K) by coupling the emission bands peaking at 410, 542 and 649 nm attributed to the contribution from Eu2+, Tb3+ and Mn2+, respectively. The results indicate the white phosphor Sr10[(PO4)5.5(BO4)0.5](BO2):Eu2+, Mn2+, Tb3+ can serve as a promising material for phosphor-converted warm white LEDs.

Green-emitting (La,M,Tb)OCl (M = Mg, Ca, and Sr) phosphors

Green-emitting (La1−x−yMxTby)OCl (0⩽x⩽0.13, 0.03⩽y⩽0.15, M=Mg, Ca, and Sr) single phase phosphors were synthesized using a liquid-phase method and their photoluminescence properties were characterized. The excitation spectrum consisted of a strong broad band from 220 to 290nm, which corresponds to the 4f–5d transition of Tb3+. The oxychloride phosphors exhibit typical emission peaks assigned to the transition from 5D4 to 7FJ (J=6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was successfully enhanced by doping divalent alkaline earth metal ions (M=Mg2+, Ca2+, and Sr2+) into La3+ sites of the host LaOCl lattice. The highest green emission intensity was obtained for (La0.88Ca0.05Tb0.07)OCl, of which the relative emission intensity was 75% of that for a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor.

Near white light emission from K+ ion compensated CaSO4:Dy3+,Eu3+ phosphors

Dy3+:Eu3+ doped calcium sulfate (CaSO4:Dy3+,Eu3+) phosphors co-doped with various K+ compensator concentrations were synthesized by recrystallization method. These orthorhombic phased phosphors showed intense multi-color near white light. The multi-color aspect ratios and the emission life times were strongly dependent on K+-concentration. These results suggest that the rare-earth (Re3+) ions are situated at the sites of Ca2+ and the site occupancy was being compensated by K+ ions. The near white light emission and large lifetimes suggest that present phosphor could be potentially applied as a blue excited white light-emitting phosphor for light emitting diodes.

LED用绿色荧光粉BaSi2N2O2∶Eu2+的发光和封装性能

The oxonitride blue-green phosphor BaSi2O2N2∶Eu2+ has been prepared by solid state reaction.The prepared BaSi2O2N2∶Eu2+ phosphors are characterized by X-ray powder diffraction(XRD),photoluminescence(PL),etc.The XRD results show that pure phase phosphors are obtained.The PL results demonstrate that BaSi2O2N2∶Eu2+ shows high efficient emission with peak at around 492 nm.The best emission can be obtained with the Eu2+ mole fraction of 4%.The phosphors are encapsulated on the ultraviolet and blue chips,high blue-green luminescence is obtained in both devices,and the CIE parameters are(0.092 0,0.428 2) and(0.112 9,0.223 0),respectively.

SINGLE-PHASED AND EMISSION-TUNABLE CaLa2-xEuxZnO5 PHOSPHORS WITH BLUE LIGHT EXCITATION FOR WLEDS

Single-phased and emission-tunable CaLa2-xEuxZnO5 phosphors were synthesized by citric sol-gel method. Precisely adjusting the activator concentration in CaLa2ZnO5 (CLZ) phosphor, we could obtain blue-green (BG) to orange-red (OR) emissions from the 5 D 2, 1, 0 → 7 FJ levels of Eu 3+ with the blue excitation wavelength of 468 nm, which perfectly matches with the emission of blue LED chip. This fascinating result has provoked us to blend the green and red color tunable single phased phosphors with and without YAG: Ce to fabricate blue LED based white light emitting diodes (LED). The emission features thus interpreted are appropriately explained through their chromaticity coordinates and energy level diagram. Besides, its thermal stability is also investigated.

Generating yellow and red emissions by co-doping Mn2+ to substitute for Ca2+ and Sc3+ sites in Ca3Sc2Si3O12:Ce3+ green emitting phosphor for white LED applications

We report luminescence properties of Ce3+ and Mn2+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnets. It is observed that Mn2+ may not only occupy Ca2+ sites to generate a yellow emission (Mn2+(I)) at 574 nm but also Sc3+ sites to generate a red emission (Mn2+(II)) at 680 nm. Considerable Mn2+ substitution for Sc3+ can be performed through balancing their charge difference by introducing a trivalent rare earth ion, such as La3+ and Ce3+, to replace Ca2+. Meanwhile, remarkable energy transfer from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) can occur, making tunable color and white light emission available in CSS:Ce3+,Mn2+ upon blue excitation into Ce3+. White LEDs combined by CSS:Ce3+,Mn2+ phosphors and blue LED chips are fabricated. A CSS:0.03Ce3+,0.2Mn2+ phosphor with deficient red emission is enriched in red by increasing Ce3+ concentration to 0.1, which leads to increase of Mn2+(II) number in case of charge compensation by more Ce3+ ions. Consequently, the color rendering index of the white LEDs is improved from 64 to 76. The results of this work indicate that CSS:Ce3+,Mn2+ garnet could be a promising single phase phosphor for white LEDs.

Preparation, characterization and luminescence of Sm 3+ or Eu 3+ doped Sr 2CeO 4 by a modified sol-gel method

Superfine Sr 2CeO 4:RE 3+ (RE=Eu, Sm) phosphors were synthesized at relatively low temperature by a modified sol-gel method using nitrates as raw materials, ethylenediaminetetraacetic acid (EDTA) as complexing agent. Single phase phosphors could be obtained at calcination temperature above 800 °C and pH value higher than 6.4 of initial solution. The as-prepared powders consisted of uniform crotch-like grains. The preparation process was monitored by thermogravimetric and differential thermal analysis (TG-DTA) and Raman spectra. The obtained products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and photoluminescence. Photoluminescence study indicated that strong energy transfer occurred between Eu 3+/Sm 3+ and host. The Sr 2CeO 4:RE 3+ emission could be tuned from blue to white and red light by varying the concentration of RE 3+. The strong emission and controllable light color are suitable for applications in advanced lighting and displaying fields.

Up-conversion fluorescence and thermal optical bistability in Gd 2O 3: 10% Yb 3+, 0.5% Tm 3+

Through a co-precipitation method Gd(OH) 3: 0.5% Tm 3+, 10% Yb 3+ powder was synthesized. After sintering at different temperatures, the as-prepared Gd(OH) 3: 0.5% Tm 3+, 10% Yb 3+ powder was changed into cubic and monoclinic phase Gd 2O 3: 0.5% Tm 3+, 10% Yb 3+ phosphors. Crystalline phases and morphologies of as-prepared powder and phosphors were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). Up-conversion (UC) fluorescence spectra of Gd 2O 3: 0.5% Tm 3+, 10% Yb 3+ phosphors were recorded by a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as the excitation source. Fluorescence decay behaviors of the phosphors were measured by exciting with 980 nm from an optical parametric oscillator (OPO) pumped by a pulsed Nd: YAG laser with a pulse duration of 10 ns and a repetition frequency of 10 Hz, and the signal was recorded using a monochromator and an oscillograph. Phase and excitation power dependent UC fluorescence properties of the phosphors were studied in detail in the article. Interestingly, the cubic phase phosphors presented thermal optical bistability phenomena. The fluorescence dynamic analysis indicated that rise and decay processes existed in the phosphor UC fluorescence.

Intense White Luminescence from Combustion Synthesized Ca12Al14O33: Yb3+/Yb2+ Single Phase Phosphor

The Ca(12)Al(14)O(33):Yb(3+)/Yb(2+) single phase nano-phosphor has been synthesized through combustion route and its luminescence and lifetime studies have been carried out up to 20 K using 976 and 266 nm excitations. The samples heated in open atmosphere have shown the presence of Yb in Yb(3+) and Yb(2+) states. The 976 nm excitation results a cooperative upconversion emission at 486 nm due to the Yb(3+) state and a broad band in the blue region and has been assigned to arise from the defect centers. The 266 nm excitation on the other hand results a broad emission band even from as-synthesized phosphor without doping of Yb, the width of which increases in presence of Yb due to the emission from Yb(2+) ions formed in heated samples. The white emission covers almost whole visible region with bandwidth 190 nm. The ions in Yb(2+) state has been found to increase with the increase in heating temperature up to 1,273 K. A back conversion of Yb(2+) to Yb(3+) has been observed for higher temperatures. Effect of boric and phosphoric acids as flux on the emission properties of Yb(3+) and Yb(2+) states have been examined and discussed. Quantum yield of emission has also been determined for different samples.

Morphology Control of High Luminance Phosphors

We report synthesis of well-grown blue phosphor powder, CaMgSi2O6:Eu2+, from new vapor phase method (Flash creation method) derived nanopowder precursor. Single phase phosphor sample was obtained by post-annealing at 1100 oC. Luminescence properties were compared with that of the sample synthesized by a conventional solid state reaction. The post-annealed sample showed intense blue emission under UV excitation.

Synthesis and luminescent properties of YGG:Tb phosphors by Pechini method

A novel green phosphor Y 3Ga 5O 12:Tb (YGG) was successfully synthesized by Pechini method. The differential scanning calorimetric (TG-DSC) analysis and X-ray powder diffraction were used to determine the crystallization temperature and the pure phase phosphors were obtained by calcining the gel at 800 °C. The morphology of the powders was characterized by scan electronic microscope (SEM). The excitation and emission spectra of photoluminescence were used to characterize the luminescent properties. The excitation spectrum is dominated by the 4f–4f5d transition of Tb 3+ at 263 nm. The strong emission peaks for the highly doped phosphors are 489 and 543 nm. YGG can be used as a kind of promising host for luminescent materials.