Blue-green Phosphor Research Articles

Luminescence properties of a novel bluish green long-lasting phosphor LiBaPO4: Eu2+, Ho3+

A novel bluish green long-lasting phosphor LiBaPO4: Eu2+, Ho3+ was synthesized by solid-state reaction. The phosphor was characterized by X-ray diffraction, photoluminescence spectra, afterglow decay curve and thermoluminescence spectrum. The photoluminescence is ascribed to the 5d-4f transitions of Eu2+ ions. There is no Ho3+ emission in the photoluminescence spectra, which means that Ho3+ is a coactivator. After irradiated with a UV light (365nm), persistent luminescence can last more than 5626s above 0.32mcd/m2, which is 100 times than the sensitivity of human eyes in dark. Thermoluminescence curves indicate that only one trap depth in the phosphor, which is ascribed to the doping of Ho3+. The possible mechanism of persistent luminescence was discussed.

Color - Tunable Phosphors in Weberite Type System, La3 SbO7 :Bi3+ , Eu3+ for Near-UV LED Applications

A new series of color tunable from yellow to near white emitting phosphors, La3SbO7:xBi3+, yEu3+ were prepared using a conventional solid state method and its structural, morphological, absorbance and photoluminescence properties and lifetime measurements were carried out to analyze the phosphor characteristics. The La3SbO7:Bi3+ phosphors crystallize into a phase pure weberite type structure with good particle morphology. Upon UV light excitation at 315 nm, these phosphors show broad band emission in the blue green region centered near 517 nm owing to the 3P1-1S0 transitions of the Bi3+ activator. Critical emission quenching of La3SbO7:xBi3+ samples was observed at x = 0.04. Eu3+ is co-doped with La3SbO7:0.04Bi3+ blue green phosphor to incorporate the red component to make a full color emission phosphor. The effective energy transfer from Bi3+ to Eu3+ ions has been assessed using Dexter's theory indicating resonance type through dipole-quadrupole interaction. Further the decreasing trends in lifetime measurements confirm the existence of energy transfer process from Bi3+ to Eu3+. The near white light emitting phosphor La3SbO7:xBi3+, yEu3+ can be realized by adjusting the concentrations of the Bi3+ and Eu3+ with chromaticity coordinates: (0.30,0.48). The above results suggest that the developed phosphor could be potential to be used as a single phase white emission phosphor for n-UV LED applications.

Effect of fluxes on synthesis and luminescence properties of BaSi2O2N2:Eu2+ oxynitride phosphors

Eu2+ activated BaSi2O2N2 oxynitride bluish-green phosphor was synthesized adopting conventional high-temperature solid-state reaction method, in which BaF2, Na2CO3 and NH4Cl were used as the fluxes. The phase formation, size distribution and microscopic morphology were characterized to investigate the influence of adding fluxes on photoluminescence properties. The results indicate that with the addition of BaF2 flux, the particle morphology becomes regular and size distribution narrows and the phase purity of BaSi2O2N2:Eu2+ phosphor can be improved effectively. The photoluminescence intensity of BaSi2O2N2:Eu2+ phosphor with BaF2 as flux gets enhanced obviously, which is much higher than that of Na2CO3, NH4Cl and without flux. The optimum content of BaF2 flux is 4 wt%, and the maximum photoluminescence intensity of the BaSi2O2N2:Eu2+ phosphor prepared with BaF2 flux rises to 141%, meanwhile, the phosphors with BaF2 flux exhibits low thermal quenching. The results indicate that the BaSi2O2N2:Eu2+ is sort of promising bluish-green phosphor for application in full-spectra LED.

Crystal structure and luminescence properties of the blue-green-emitting Ba9 (Lu, Y)2 Si6 O24 :Ce3+ phosphor.

Samples of the Ba9 (Lu2-x Yx )Si6 O24 :Ce3+ (x=0-2) blue-green phosphors were synthesized by solid-state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y3+ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y3+ (r=0.900Å) compared with that of Lu3+ (r=0.861Å). Under 400nm excitation, samples exhibited strong blue-green emissions around 490nm. The emission bands had a slight blue shift that resulted from weak crystal-field splitting with increasing Y3+ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y3+ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y-series. The excitation band peak around 400nm matched well with the emission light from the efficient near-ultraviolet (NUV) chip. These results indicate promising applications for these NUV-based white light-emitting diodes.

Blue green fluorescence from freestanding films of PVDF/ZnS:Cu Nanocomposites

The growth of a novel nanocomposite consisting of Poly Vinylidene Di Fluoride (PVDF) and copper doped zinc sulphide (ZnS:Cu), its realization as flexible freestanding films and its application prospects as a bluish green phosphor form the essence of the work presented in this paper. PVDF is a semicrystalline fluoro polymer with the repeat unit of CH2-CF2.The photoluminescence emission characteristics were investigated in detail for various concentrations of ZnS:Cu in the nanocomposite films. The highlight of the present work is the observation that these luminescent films can be easily peeled off to yield free standing films which are quite stable and flexible.

Sol-gel synthesized Sr4Al14O25:Eu2+/Dy3+ blue–green phosphorous as oxygen sensing materials

In this study, we utilized newly synthesized Sr4Al14O25:Eu2+/Dy3+ blue–green phosphors along with silver nanoparticles (AgNPs) for fabrication of oxygen sensitive materials. To the best of our knowledge oxygen sensing mechanism of the offered design is totally different from the previously published works. One-component silicone: poly (1-trimethylsilyl-1-propyne), two component phenyl bearing silicone, plasticized polymethylmethacrylate, and ethylcellulose (EC) were tested as matrix materials. Electrospun fibers, porous and smooth thin films were produced by electrospinning or knife coating technique. Oxygen induced luminescence of the phosphors at 544 nm was followed as the analytical signal. Utilization of silver nanoparticles in silicone along with phosphors resulted with a 7.14 fold enhancement in the signal intensity and significant spectral response towards oxygen competing with the signals of the oxygen sensors utilizing metalloporphyrins or ruthenium complexes. We observed high sensitivity and stability, increased surface area and an enhancement in all sensor dynamics. Linearity of the calibration plots was superior for the pO2 range of 0.0–20.0% with respect to the previously reported ones. When stored at the ambient air of the laboratory there was no significant drift in signal intensity after 12 months. Our sensitivity and stability tests are still in progress.

Synthesis and photoluminescence properties of KBaY(BO3)2:Eu2+ bluish-green phosphor

The bluish-green KBaY(BO3)2:Eu2+ phosphors were prepared by high-temperature solid state reaction method. The photoluminescence properties, concentration quenching and energy transfer as well as the luminescence decays were investigated. The emission spectrum showed a single intensive band centered at 500 nm, which correspond to the 4f 65d 1 → 4f 7 transition of Eu2+. The optimal concentration for the luminescence of Eu2+ in KBaY(BO3)2:Eu2+ was determined to be 0.03 mol. The critical energy transfer distance was calculated as 21.34 A. The corresponding concentration quenching mechanism was verified to be a dipole–dipole interaction. And the blue-shift behavior of KBaY(BO3)2:Eu2+ with increasing temperature was analyzed by the configurational coordinate diagram. The results indicate that the KBaY(BO3)2:Eu2+ phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang.

Circadian-effect engineering of solid-state lighting spectra for beneficial and tunable lighting.

Optimization of solid-state lighting spectra is performed to achieve beneficial and tunable circadian effects. First, the minimum spectral circadian action factor (CAF) of 2700 K white light-emitting diodes (LEDs) is studied for applications where biologically active illumination is undesirable. It is found that white-LEDs based on (i) RGB chips, (ii) blue & red chips plus green phosphor, and (iii) blue chip plus green & red phosphors are the corresponding minimum-CAF solutions at color-rendering index (CRI) requirements of 80, 90, and 95, respectively. Second, maximum CAF tunability of LED clusters is studied for dynamic daylighting applications. A dichromatic phosphor-converted blue-centered LED, a dichromatic phosphor-converted green-centered LED, and a monochromatic red LED are grouped to obtain white spectra between 2700 K and 6500 K. A maximum CAF tunability of 3.25 times is achieved with CRI above 90 and luminous efficacy of radiation of 313 - 373 lm/W. We show that our approaches have advantages over previously reported solutions on system simplicity, minimum achievable CAF value, CAF tunability range, and light source efficacy.

Synthesis and luminescence properties of bluish-green emitting K2MgSi3O8:Eu2+ phosphor

AbstractEu2+-doped K2MgSi3O8 phosphors were synthesized by conventional solid-state reaction method. The phase formation of as-prepared samples was characterized by X-ray powder diffraction. The luminescence properties were investigated by the photoluminescence excitation and emission spectra, decay curve and CIE coordinates. The phosphor showed bluish-green emission centered at 460 nm under the excitation of UV and near UV light with the wavelength range of 250–430 nm. Two Eu2+ emission centers existed in the K2MgSi3O8:Eu2+ phosphor according to the luminescence spectra and the decay curves. The critical quenching concentration of Eu2+ doping was determined to be 3.0 mol.% and the concentration quenching mechanism was dipole-dipole interactions between Eu2+ ions. These results suggested that K2MgSi3O8:Eu2+ was a potential bluish-green phosphor candidate for white UV-LED.

Preparation and photoluminescence of Ba substitution in blue–green phosphors Ba Zn1−Al2O4: Eu2+

Abstract Zinc dialuminium oxide, ZnAl2O4 is well-known phosphor host material with spinel structure. Ba substituted compositions, BaxZn1−xAl2O4: Eu2+ (with x = 0.3–1.0) co-doped with 1 mol% Eu have been synthesized by the high-temperature solid-state method. The structure, morphology and luminescent properties of the phosphors have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence techniques. Effect of Ba substitution on structure and photoluminescence has been investigated. The prepared BaxZn1−xAl2O4: Eu2+ phosphors change structure from cubic to clinic with the increasing Ba concentration. The SEM images demonstrate that the grain sizes vary ranging from a few to ten microns with polycrystalline morphology. Photoluminescence characteristic shows intense emission for BaxZn1−xAl2O4: Eu2+ in the blue–green region (λmax = 495 nm) with the strongest emission at x = 0.8 of Ba concentration. The blue–green emission corresponds to transition from 4f65d1 to 4f7 of Eu2+ ion.

Luminescent Properties of Sr4Si3O8Cl4:Eu2+, Bi3+ Phosphors for Near UV InGaN-Based Light-Emitting-Diodes

Sr4Si3O8Cl4 co-doped with Eu2+, Bi3+ were prepared by the high temperature reaction. The structure and luminescent properties of Sr4Si3O8Cl4:Eu2+, Bi3+ were investigated. With the introduction of Bi3+, luminescent properties of these phosphors have been optimized. Compared with Sr3.90Si3O8Cl4:0.10Eu2+, the blue-green phosphor Sr3.50Si3O8Cl4:0.10Eu2+, 0.40Bi3+ shows stronger blue-green emission with broader excitation in near-UV range. Bright blue-green light from the LED means this phosphor can be observed by the naked eye. Hence, it may have an application in near UV LED chips.

Eu2+-sensitized Sr6Ca4(PO4)6F2:Tb3+ phosphors: An investigation on their luminescence and energy transfer

A novel series of Sr6Ca4(PO4)6F2:Eu2+,Tb3+ (SCPF:Eu2+,Tb3+) powder samples is synthesized using a high-temperature solid-state method. X-ray diffraction, FT-IR spectra, photoluminescence spectroscopy and quantum efficiency are used to characterize the as-prepared samples. Excited by near-ultraviolet radiation, tunable color tone is obtained for Eu2+ and Tb3+ co-doped SCPF samples by adjusting doping concentration. Energy transfer from Eu2+ to Tb3+ in SCPF phosphor is also investigated at a critical distance of 28.09Å. Corresponding chromaticity coordinates are calculated based on the emission band. Results suggest that SCPF:Eu2+,Tb3+ is a promising blue-green phosphor for light-emitting diodes or displays.

Synthesis of mono-phase La2Si6O3N8:Ce3+,Tb3+ blue-green phosphors with direct silicon nitridation and their photoluminescence properties

Mono-phase La2Si6O3N8:Ce3+ phosphors co-doped with Tb3+ were produced via a direct silicon nitridation (DSN) method at 1500°C. The produced phosphors were characterized with regards to their crystalline structure, microstructure, photoluminescence properties, and lifetime. The decay mode of Ce3+ suggests that energy transfer occurs in La2Si6O3N8:Ce3+,Tb3+ phosphors. Intense green emission was recorded from La1.4Si6O3N8:0.2Ce3+,0.4Tb3+ and qualifies these phosphors for further consideration as promising candidates for ultraviolet convertible phosphors in light-emitting devices.

Synthesis, structure and optical properties of cerium-doped calcium barium phosphate – a novel blue-green phosphor for solid-state lighting

A new blue-green phosphor, Ca6BaP4O17:Ce3+, which can be prepared by conventional solid-state synthesis, is reported as a candidate phosphor for solid-state lighting with near-ultraviolet LEDs.

Ce<SUP>3+</SUP>/Tb<SUP>3+</SUP> co-doped KBaY(BO<SUB>3</SUB>)<SUB>2</SUB>: A color-tunable blue-green phosphor for near-UV white LEDs

Ce<SUP>3+</SUP>/Tb<SUP>3+</SUP> co-doped KBaY(BO<SUB>3</SUB>)<SUB>2</SUB>: A color-tunable blue-green phosphor for near-UV white LEDs

Spectral optimization of color temperature tunable white LEDs with excellent color rendering and luminous efficacy.

The optimization model of limited luminous efficacy (LLE) for correlated color temperature (CCT) tunable phosphor-coated white light-emitting diodes (pc-W LEDs) consisting of blue chips, green and yellow phosphors, and red chips, including downconversion energy loss, has been developed under the constraint of a designated color-rendering index (CRI) and a special CRI of R9 for strong red. The optimal spectra of pc-W LEDs are obtained with a nonlinear program for maximizing LLE under conditions of both CRI and R9 above 90, 95, and 98 at CCTs of 2700-6500 K. The pc-W LEDs with LLE>301 lm/W for both CRI and R9 above 90, LLE>290 lm/W for both CRI and R9 above 95, and LLE>276 lm/W for both CRI and R9 above 98 could be achieved at CCTs of 2700-6500 K. The recommended peak wavelengths and full widths at half-maximum (FWHMs) for the current LEDs and phosphors and their photometric and colorimetric performances are presented.

A Novel Single-Source Precursor Route for the Synthesis of Blue-Green Phosphor SrS:Ce3+

A Novel Single-Source Precursor Route for the Synthesis of Blue-Green Phosphor SrS:Ce3+

Dy<sup>3+</sup> Doping Blue-Green Sr<sub>4</sub>Al<sub>14</sub>O<sub>25</sub>:Eu<sup>2+</sup> Phosphor for Enhancing Luminescent Properties and the Mechanism Study

Dy3+ doped blue-green Eu2+ doped strontium aluminate (Sr4Al14O25:Eu2+) phosphor was prepared using a high temperature solid state method and the influence of the doped Dy3+ on the luminescent properties was studied using X-ray diffraction, scanning electron microscopy, fluorescence spectroscopy and a series of other characterization methods. It is found that Dy3+ doping can enhance the luminescent intensity and extend the afterglow time. The luminescent mechanism of rare earth ions doped strontium aluminate phosphor was also discussed deeply, the effects of the doping amount on the luminescent properties has been made detailed explanation and description. This work has important theoretical significance for the development of higher brightness and longer afterglow blue-green phosphors.

Two-color emitting of Eu2+ and Tb3+ co-doped Sr2MgSi2O7 for UV LEDs

An intense bluish green phosphor, Sr2MgSi2O7: Eu2+, Tb3+, was synthesized by high temperature solid-state reaction. The photoluminescence excitation and emission spectra, the lifetime, concentration effect and the temperature-dependent properties are investigated in detail. The results show that an efficient nonradiative energy transfer from Eu2+ to Tb3+ occurs. Tb3+ ions give an intense green emitting light by a strong excitation band of Eu2+ ions at 350–430nm, matching well with the dominant emission band of (n)-UV (350∼420nm) LEDs. These results demonstrate that Tb3+ ion with low 4f–4f absorption efficiency in (n)-UV region can play a role of activator in narrow green emitting phosphor potentially useful in (n)-UV GaN-based LED through efficient energy feeding by allowed 4f–5d absorption of Eu2+ with high oscillator strength.

The effect of different lattice sites substitution on photoluminescence characteristics of Eu2+/Ce3+ doped M5(ZO4)3X

The empirical formula of Van Uitert is applied to calculating the emission wavelengths of haloapatite and silicon apatite phosphors doped with Eu2+/Ce3+. The relationship between emission wavelengths and occupied lattice sites of Eu2+/Ce3+ is discussed in haloapatite crystal. For phosphors of haloapatite and silicon apatite doped with Eu2+, the emission bands of the long-wave region are interpreted reasonably. Phosphors Sr5(PO4)2SiO4 doped with Eu2+/Ce3+ are synthesized by high temperature solid state reaction under two different atmospheres, the spectral characteristics of Eu2+/Ce3+ occupying different lattice sites are studied. The luminescent materials Sr5(PO4)2SiO4 doped with Eu2+/Ce3+ are promising blue-green phosphors for application in white-LEDs.