Blue-green Phosphor Research Articles

Photoluminescence properties of Eu2+-doped Ba3Si6O9N4 phosphors synthesized by a gas reduction nitridation method for white light emitting diodes

A series of Eu2+-activated Ba3Si6N9O4 blue-green phosphors was synthesized using a gas reduction nitridation method with NH3 gas. The x-ray diffraction (XRD) pattern of the synthesized phosphors sintered at 1300 °C was well matched to the reference peaks. The synthesized Ba3Si6N9O4:Eu2+ phosphors absorbed light from the 350–470 nm region. The emission spectrum (monitored at λem = 494 nm) increased with increasing maintenance time using NH3 gas. The highest emission intensity was observed when the maintenance time was 12 h. In the XRD patterns, the relative intensity of the phosphors shows a maximum at a maintenance time of 12 h. On the other hand, maintaining for 12 h showed the best result. Also the Ba3Si6N9O4 phosphor exhibited strong thermal properties compared to the commercial phosphor. The green-emitting Ba3Si6N9O4:Eu2+ phosphors obtained could be applied as white light emitting diodes.

Quasiparticle electronic structure of barium-silicon oxynitrides for white-LED application

Ba${}_{3}$Si${}_{6}$O${}_{12}$N${}_{2}$:Eu${}^{2+}$ and Ba${}_{3}$Si${}_{6}$O${}_{9}$N${}_{4}$:Eu${}^{2+}$ have strikingly similar atomistic structures, but the former is an efficient green phosphor at working temperature while the latter is a bluish-green phosphor whose luminescence decreases quite fast with temperature. Aiming at the understanding of such different behavior, we compute the quasiparticle electronic band structure of the two hosts, Ba${}_{3}$Si${}_{6}$O${}_{12}$N${}_{2}$ and Ba${}_{3}$Si${}_{6}$O${}_{9}$N${}_{4}$, thanks to many-body perturbation theory in the ${G}_{0}{W}_{0}$ approximation. The gap differs by about 0.43 eV. We analyze the eigenfunctions at the top of the valence band, at the bottom of the conduction band, and also the chemical shifts for the Ba site in the two hosts. The valence bands, directly impacted by the different stoichiometric ratio, are not thought to play a large role in the luminescence. Deceivingly, the dispersive bottom of the conduction band, directly related to luminescent properties, is similar in both compounds. The spatial topology of the probability density of the bottom of the conduction bands differs, as well as the location of the 5d peak, with a much higher energy than the bottom of the conduction band in Ba${}_{3}$Si${}_{6}$O${}_{12}$N${}_{2}$ than in Ba${}_{3}$Si${}_{6}$O${}_{9}$N${}_{4}$. Electromagnetic absorption spectra are also computed for both compounds.

An Efficient, Thermally Stable Cerium-Based Silicate Phosphor for Solid State White Lighting

A novel cerium-substituted, barium yttrium silicate has been identified as an efficient blue-green phosphor for application in solid state lighting. Ba9Y2Si6O24:Ce(3+) was prepared and structurally characterized using synchrotron X-ray powder diffraction. The photoluminescent characterization identified a major peak at 394 nm in the excitation spectrum, making this material viable for near-UV LED excitation. An efficient emission, with a quantum yield of ≈60%, covers a broad portion (430-675 nm) of the visible spectrum, leading to the blue-green color. Concentration quenching occurs when the Ce(3+) content exceeds ≈3 mol %, whereas high temperature photoluminescent measurements show a 25% drop from the room temperature efficiency at 500 K. The emission of this compound can be red-shifted via the solid solution Ba9(Y(1-y)Sc(y))(1.94)Ce(0.06)Si6O24 (y = 0.1, 0.2), allowing for tunable color properties when device integration is considered.

Efficient bluish-green phosphorescent iridium complex for both solution-processed and vacuum-deposited organic light-emitting diodes

Iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) is one typical bluish-green phosphor widely used in phosphorescent organic light-emitting diodes (PhOLEDs). In order to optimize its electroluminescent performance, 3,6-(di-tert-butyl)carbazolyl was introduced into the pyridine ring of the 2,4-difluorophenyl-pyridine ligand via a non-conjugated CH2 linkage. The generated 3,6-di-tert-butyl-9-((6-(2,4-difluorophenyl)pridine-3-yl)methyl)-9H-carbazole (Cz-CH2-dfppy) was used as cyclometalating ligand to prepare iridium complex 1, (Cz-CH2-dfppy)2Ir(pic). In comparison with the case to attach carbazole directly on pyridine, this non-conjugated CH2 linking strategy avoids the unwanted bathochromic shift of the phosphorescence and improves the solubility of the iridium complex. (Cz-CH2-dfppy)2Ir(pic) (1) was used as doped emitter to fabricate OLEDs by both spin-coating and vacuum evaporation methods. Efficient bluish-green electrophosphorescence was obtained with maximum luminance efficiency of 22cd/A (14lm/W, 8.7%) and 26cd/A (12lm/W, 9.5%) for the solution-processed and vacuum-deposited devices, respectively, which far exceed those of the parent Firpic based device. The improved performance for (Cz-CH2-dfppy)2Ir(pic) was interpreted in terms of improved charge balance brought by the presence of the carbazole groups in the ligands.

A new photostimulated strontium-aluminate-based blue-green phosphor

We have proposed, experimentally demonstrated, and implemented a technique for producing a new photostimulated blue-green phosphor with increased photostimulated luminescence intensity via additional doping of the Sr4Al14O25:Eu,Tm phosphor with La3+. The photostimulated phosphor (FV-490M) has been commercialized and is used most widely in security and authentication applications, both as an individual phosphor and in combination with the photostimulated red phosphor SrS:Eu,Sm. When IR-stimulated, the combination phosphor exhibits a dynamic visual kinetic effect.

Giant Improvement on the Afterglow of Sr4Al14O25:Eu2+,Dy3+ Phosphor by Systematic Investigation on Various Parameters

Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+ blue-green phosphor with different B3+, Eu2+, Dy3+, and Ag+ contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H2 in N2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40 mol% H3BO3 showed dense and pure Sr4Al14O25 phase with higher emission intensity, but in the samples containing less than 20 mol% H3BO3 mixed phases consisting of Al2O3, SrAl12O19 and SrAl2O4 were observed, while in higher H3BO3 content, SrAl2B2O7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd·m−2 and the longest persistency of greater than 30 hours over the value of 5 mcd·m−2, higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses.

Preparation and photoluminescence properties of single-phase Ca2SiO3Cl2:Eu2+ bluish-green emitting phosphor

Using CaO/CaCO3 (blend) and NH4Cl as the respective calcium and chloride sources, we have succeeded in the synthesis of single-phase Ca2SiO3Cl2:Eu2+ powder phosphor via solid-state-reaction. Indeed, two emission bands due to Eu2+ should be observed in Ca2SiO3Cl2:Eu2+, since there are two Eu2+ luminescence centers substituting for two Ca2+ sites. However, interestingly, only one emission band centered at 495nm is observed. This is explained based on the uniform covalency and crystal field of two Eu2+ sites. The excellent thermal stability and the intense emission upon near-ultraviolet (UV) light excitation suggest that Ca2SiO3Cl2:Eu2+ can be used as a potential bluish-green phosphor for near-UV white LEDs.

Two phosphor converted white LED with improved CRI

Most of the commercial white LED lamps use blue chip coated with yellow emitting phosphor. Use of blue excitable red and green phosphors is expected to improve CRI. Several phosphors such as SrGa2S4:Eu2+, (Sr,Ba)SiO4:Eu2+ have been suggested in the past as green components. However, there are issues of sensitivity and stability of such phosphors. Here, we describe gallium substituted YAG:Ce3+ phosphor as a green emitter. YAG structures are already accepted by the industry for the stability and efficiency. LED’s with improved CRI could be fabricated by choosing Y3Al4GaO12:Ce3+ (green and yellow) and SrS:Eu2+ (red) phosphors along with blue chip.

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.

A bluish green chlorosilicate phosphor for UV based white LEDs

A bluish green phosphor divalent (Eu 2+) doped calcium chlorosilicate (Ca 7(SiO 4) 2Cl 6:Eu 2+) was synthesized by conventional solid state reaction method and its luminescent property was investigated in this paper. The strong crystal field splitting made the broad excitation band extend from UV to visible region. The emission spectrum was composed of two broad bands that peaked at 418 and 502 nm, respectively. The color parameters of the device combining with Ca 7(SiO 4) 2Cl 6:Eu 2+ and CaMoO 4:Eu 3+ phosphor were measured. The results indicated that this phosphor was a better candidate for UV based white LED.

Luminescent properties of long-lasting BaAlxOy:Eu2+,Dy3+ nanocomposites

BaAlxOy:Eu2+,Dy3+ blue-green phosphor samples were synthesized by a combustion method at the low temperature of 500°C. Phosphor nanocrystallites with high brightness were obtained without significantly changing the crystalline structure of the host. The crystallite sizes determined from the Scherrer equation ranged between 34 and 41 nm. Different volume fractions of the BaAlxOy:Eu2+,Dy3+ powder were then introduced in LDPE polymer. The resulting composites were similarly analyzed and also thermally characterized by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). PL results indicate that the LDPE-phosphor interface, which is considered to have an influence on the composite behavior, did not significantly change the spectral positions of the phosphor materials, whose major emission peaks occurred at about 505 nm. The improved afterglow results for the composites may have been caused by morphological changes due to increased surface area and defects. Thermal results indicate that the BaAlxOy:Eu2+,Dy3+ particles acted as nucleating centers and enhanced the overall crystallinity in the LDPE nanocomposite while preventing lamellar growth, hence reducing the crystallite sizes in LDPE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Luminescence properties of Eu2+-activated Ca0.13Sr0.87Al2Si2O8: A bluish green phosphor for solid state lighting

Eu2+ activated phosphors with the composition of Ca013Sr0.87Al2Si2O8 were synthesized by combustion technique. The luminescent properties of these phosphors have been explored by analyzing their excitation and emission spectra with the help of photoluminescence (PL) spectroscopy. The phase-forming processes and presence of associated mode of vibrations of the phosphors were studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) respectively. Under ultra-violet (UV) excitation, Ca013Sr0.87Al2Si2O8 phosphors had broad emission spectrum between 418 and 550 nm in the blue-green region of spectra corresponding to 4f65d→4f7 transition of Eu2+ ion. The results show Ca013Sr0.87Al2Si2O8: Eu2+ is a promising host candidate for the phosphors and can be used for improving the efficiency and quality of phosphor-converted white light-emitting diodes.

Luminescent Properties of Ba2(Mg, Zn)Si2O7:Eu2+ Particles as Potential Blue-Green Phosphors For Ultraviolet Light-Emitting Diodes

Ba2−xMg1−yZnySi2O7:Eux2+ blue–green phosphor particles were prepared by combustion-assisted synthesis method as the fluorescent material for ultraviolet light-emitting diodes (UV-LEDs), performing as a light source. The luminescent properties were investigated by changing the postannealing temperature, the concentration of the activator, and the ratio of Zn to Mg. The crystallinity and luminescence were investigated by using an X-ray diffractometer and a luminescence spectrometer. The pure monoclinic Ba2MgSi2O7 and Ba2ZnSi2O7 phases were formed when the posttreatment temperature was 1000°C. It was found that the introduction of Zn2+ into Ba2MgSi2O7:Eu2+ effectively increased its emission. The emission spectra presented an emission position red shift of up to 5 nm from Ba2Mg Si2O7:Eu2+ to Ba2ZnSi2O7:Eu2+, which is correlated with the effect of Zn2+ substituting for Mg2+ sites. The excitation spectrum of Ba2ZnSi2O7:Eu2+ was a broad-band extending from 260 to 465 nm, which matches the emission of UV-LEDs.

Synthesis and photoluminescence of a novel Sr-SiAlON:Eu 2+ blue-green phosphor (Sr 14Si 68− sAl 6+ sO sN 106− s:Eu 2+ ( s ≈ 7))

A novel Eu 2+ activated Sr-SiAlON oxynitride phosphor, with the chemical composition of Sr 14Si 68− s Al 6+ s O s N 106− s :Eu 2+ ( s ≈ 7), was synthesized by firing the powder mixture of SrO, SrSi 2, α-Si 3N 4, AlN and Eu 2O 3 at 1900 °C for 6 h under 1 MPa nitrogen atmosphere. The structure has a typical feature of SiAlON consisting of the host framework which is constructed by a three-dimensional MX 4 tetrahedral (M: Si or Al; X: O or N) network, and Sr or Eu 2+ ions as the guest ions. It has been shown that the Sr-SiAlON:Eu 2+ phosphor has the excitation band covering the range of the ultraviolet light region to 500 nm, and exhibits an intense blue-green color with the emission band centered at about 508 nm. The temperature dependent emission intensity of the Sr-SiAlON:Eu 2+ phosphor is better than that of a typical blue-green Ba 2SiO 4:Eu 2+ phosphor. It is demonstrated that Sr-SiAlON:Eu 2+ phosphor is very promising for use in white -LEDs.

5d Levels of rare-earth ions in oxynitride/nitride phosphors: To what extent is the idea covalency reliable?

It is often said that promising phosphors for white-LEDs are Ce 3+/Eu 2+-doped multinary oxynitrides/nitrides, mainly because they are more covalent than conventional oxide phosphors so as to be effectively excited by blue or near-ultra-violet light. In this paper, detailed discussions are given to clarify factors affecting 5d levels of the rare-earth ions in nitride/oxynitride phosphors by examining some examples: LaSi 3N 5:Ce (blue phosphor)/La 3Si 6N 11:Ce (yellow phosphor) and BaSi 2O 2N 2:Eu (bluish green phosphor)/Ba 3Si 6O 9N 4:Eu (bluish green phosphor)/Ba 3Si 6O 12N 2:Eu (green phosphor). It is stressed that dielectric constant/refractive index (as an indicator of polarizability of ligand) along with coordinate bond length should be examined rather than covalency to grasp the trend of 4f–5d transitions. For this purpose, some useful rules-of-thumb are addressed.

Two-color emitting of Ce^3+ and Tb^3+ co-doped CaLaGa_3S_6O for UV LEDs

An intense bluish-green phosphor, CaLaGa(3)S(6)O:Ce(3+),Tb(3+), is developed. The photoluminescence excitation and emission spectra, the lifetime, and the concentration effect are investigated. The results show that an efficient nonradiative energy transfer from Ce(3+) to Tb(3+) occurs and its efficiency is about 11%. Although the efficiency is not high enough, these results demonstrate that a Tb(3+) ion with low 4f-4f absorption efficiency in the near-UV [(n)-UV] region can play the role of activator in a narrow green-emitting phosphor. This is potentially useful in (n)-UV (380-420 nm) GaN-based LEDs through efficient energy feeding by allowing 4f-5d absorption of Ce(3+) with high oscillator strength.

A promising blue–green emitting phosphor for white light-emitting diodes prepared by sol–gel method

Abstract (Ba 2− x Eu x )ZnSi 2 O 7 blue–green phosphors were prepared by a sol–gel (SG) process. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TG). The properties of the resulting phosphors were characterized by photoluminescence (PL) spectroscopy. The shape and size of the sample were observed by transmission electron microscopy (TEM). The results of TG and XRD indicate that the (Ba 2− x Eu x )ZnSi 2 O 7 phosphors crystallize completely at 900 °C. The emission spectrum shows a single band centered at 500 nm, which corresponds to the 4 f 6 5 d 1 → 4 f 7 transition of Eu 2+ . The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu 2+ in Ba 2 ZnSi 2 O 7 :Eu 2+ phosphor is about 0.10 mol. The value of the critical transfer distance is calculated as 15.1 A. The corresponding concentration quenching mechanism is verified to be the electric multipole–multipole interaction.

Monochromatic blue-green and red emission of rare-earth ions in MgGa 2O 4 spinel

Pr 3+-activated blue-green phosphor and Eu 3+-activated red phosphor hosted in MgGa 2O 4 spinel have been prepared by a gel-assisted high-temperature calcination process, respectively. Both anion and cation vacancies in the host were formed by decreasing the Mg concentration in the reaction source. The induced vacancies provide possibility of the accommodation of the doped rare-earth ions with larger atomic size in the highly symmetrical spinel structure. Due to the efficient energy transfer from the spinel host to the sole 4f sub-level of the doped rare earths, monochromatic emissions with high efficiency can be obtained to allow the phosphors to find applications in solid-state laser device and other phosphors excited under low energy. The corresponding spectroscopic transition mechanism has been proposed in this work.

Effect of B2O3 on the Photoluminescence Properties of Sr4Al14O25: Eu2+, Dy3+ Phosphor

ABSTRACT An efficient blue-green phosphor, Sr4Al14O25: Eu2+, Dy3+, was prepared by solid-state synthesis method. B2O3 was used as a flux for the synthesis of phosphorous materials. The different mol % of B2O3 was employed during the synthesis. X-ray powder diffraction (XRD) confirmed the formation of Sr4Al14O25: Eu2+, Dy3+ phosphor in an orthorhombic phase. The synthesized phosphorous materials were further investigated by XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence studies. The phosphor, Sr4Al14O25: Eu2+, Dy3+ shows broad band ultraviolet (UV) excited luminescence in the blue-green region (λmax= 491 nm) due to the transition from the 4f6 5d1 to the 4f7 level of the Eu2+ ion. The phosphorous material with 75 mol % of B2O3 shows high brightness and long persistent luminescence whereas the phosphorous material without B2O3 shows no emission and persistence of luminescence.

Luminescence properties of Eu 2+-activated Ca 12Al 10.6Si 3.4O 32Cl 5.4: A promising phosphor for solid state lighting

In this article, we synthesized and characterized a novel bluish green phosphor for white light-emitting diodes, Eu 2+-activated Ca 12Al 10.6Si 3.4O 32Cl 5.4. The phosphor shows broad and strong absorption in the region (320–450 nm), which is essential for improving the efficiency and quality of white light-emitting diodes. When excited at 380 nm, the phosphor shows two emission bands at around 425 and 500 nm. The main emission peak of Eu 2+-activated Ca 12Al 10.6Si 3.4O 32Cl 5.4 exhibits red shift in comparison with that of Eu 2+-activated Ca 12Al 14O 33, which is due to the introduction of Si and Cl ions. The results show Ca 12Al 10.6Si 3.4O 32Cl 5.4 is a promising host candidate for the phosphors.