Green-yellow Phosphor Research Articles

A metal-to-metal charge transfer induced green-yellow phosphor CsAlGe2O6:Bi3+ for full-spectrum LED devices.

With the development of solid-state lighting, full-spectrum lighting has gradually received extensive attention. Until now, Bi3+-doped narrow-band blue phosphors have been widely reported, but broadband green-yellow Bi3+-doped luminescent materials generated by metal-to-metal charge transfer have been rarely reported. In this study, a Bi3+ ion doped germanate luminescent material CsAlGe2O6:x%Bi3+ (1 ≤ x ≤ 11) is synthesized by a high-temperature sintering method. The phosphor can generate a broad green-yellow band peaking at 535 nm with a full width at half maximum of 165 nm under ultraviolet radiation. Through the analysis of the coordination environment, photoluminescence spectra and decay curves, the broadband emission spectra of Bi3+ ions are proved to be generated by the metal-to-metal charge transfer state and the 3P1 → 1S0 transition. By using theoretical research, luminescence kinetics, and Gaussian fitting, the luminescence mechanism of Bi3+ is examined. Meanwhile, the high quantum efficiency and superior thermal stability prove that the phosphor can be used as an efficient luminescent material in the field of full-spectrum LED devices.

Hue dual-chromatic calcium chlorosilicate phosphor for light-emitting diode having yellow and white illumination

<p><span>High-thermal solid phase reactions produced a series of bright green-yellow phosphors called Ca<sub>3</sub>SiO<sub>4</sub>Cl<sub>2</sub>,Eu<sup>2+</sup>,Mn<sup>2+ </sup>(CaM). For example, powder dispersed reflection, photoluminescence excitation (PE), and along with emission spectra, were used to determine their luminous characteristics at between 10 K and 450 K of temperature. While the CaM exhibits wide absorption bands in the 250-450 nm range, which matches the near-uv of the InGaN-based chips, they also display two dominant absorptions, attributed to the 5d → 4f Eu<sup>2+</sup> transformation, as well as the <sup>4</sup>T<sub>1g</sub>(<sup>4</sup>G) → <sup>6</sup>A<sub>1g</sub>(<sup>6</sup>S) transfer of the two ions Eu<sup>2+</sup> and Mn<sup>2+</sup>, respectively. Increasing the concentration of Mn<sup>2+</sup> ion reduces the lifespan of the Eu<sup>2+</sup> ion. This encourages an efficient energy exchange between these two ions. The UV light leakage issue in yellow LEDs was resolved by intergrating with n-UV InGaN chips and CaM. Powerful white LEDs were then created by mixing blue chlorophosphate with CaM. Its color coordinate was (0.3281,0.3071), and the associated color temperature (TC) was 6065 K, while the general hue rendering (Ra) and illuminating effectiveness (11 lm/W) were respectively 84.5 and 11 lm/W.</span></p>

Etendue maintained white solid-state light generation by light emitting diodes pumped green aluminate green-yellow phosphor

We propose a technique to generate etendue maintained white light. The proposed technique uses three high-power blue light emitting diodes (LEDs) with identical characteristics to pump green aluminate (GAL) green-yellow phosphor coated on the inner channel of a waveguide. The technique offers two methods of generation of white light. Standalone partial conversion of blue to green and yellow light by GAL phosphor, combined with unconverted blue light, produces white light homogenized within the light guide. Complete conversion of blue to green and yellow light with the further addition of blue and red wavelengths from additional LED sources multiplexed with the output is also possible to further increase total white light output. Following design and optical modeling to prove the concept, the proposed technique is demonstrated, which shows white light emissions from the waveguide with no increase in aperture size while the original LED etendue is maintained. The proposed technique offers an alternative to low-lifetime, low-efficiency xenon lamps for light sources in etendue critical applications such as endoscopy.

Synthesis, properties, and package of Eu2+ doped green-yellow Ba(Ca)SiO(N) phosphors in NUV LED

In the study, a two-step high temperature solid state reaction method was applied to synthesize the green and green-yellow phosphors of 0.5 mol% Eu2+ doped Ba2SiO4, mixture of Ba3Si6O9N4 and Ba2SiO4, CaSi2O2N2. X-ray diffraction (XRD), scanning electron microscope (SEM), diffuse reflection (DR) spectra, photoluminescence (PL) excitation and emission spectra, thermal stability behavior, and luminescent decay curves were employed to analyze these phosphors. In the first step reaction, Eu3+ present weak red or orange-red emission. After reduction from Eu3+ to Eu2+ in the N2(95%)–H2(5%) atmosphere in the second reaction step, the Eu2+ presented bright green or green-yellow light under near ultraviolet (NUV) excitation. By combining the phosphors with NUV chips, the obtained LEDs gave bright light under forward bias current. The obtained green and green yellow materials can be used in phosphor converted based LEDs.

Synthesis and Luminescence Properties of a Novel Green-Yellow-Emitting Phosphor BiOCl:Pr3+ for Blue-Light-Based w-LEDs.

The development of white-light-emitting diodes (w-LEDs) makes it meaningful to develop novel high-performance phosphors excited by blue light. Herein, BiOCl:Pr3+ green-yellow phosphors were prepared via a high-temperature solid-state reaction method. The crystal structure, luminescent properties, lifetime, thermal quenching behavior, and quantum yield were studied in detail. The BiOCl:Pr3+ phosphors presented several emission peaks located in green and red regions, under excitation at 453 nm. The CIE coordinates could be tuned along with the changed doping concentration with fair luminescence efficiency. The results also indicated that the optimized doping concentration of Pr3+ ions was at x = 0.0075 because of the concentration quenching behavior resulting from an intense exchange effect. When the temperature reached 150 °C, the intensity of the emission peak at 495 nm could remain at 78% of that at room temperature. The activation energy of 0.20 eV also confirmed that the BiOCl:Pr3+ phosphor exhibited good thermal stability. All these results indicate that the prepared products have potential to be used as a high-performance green-yellow-light-emitting phosphor for blue-light-based w-LEDs.

Spectroscopic investigation and interest of Pr3+-doped calcium aluminosilicate glass

Abstract In this report, Pr3+-doped calcium aluminosilicate (CAS) glasses were synthesized and their spectroscopic properties investigated. The present subject was motivated by the red emission of the Pr3+ ion that can be combined with the green-yellow emission of other luminescent ions like Ce3+ or Eu2+ for white light generation. This combination of materials has been required since commercial diode devices for white lighting exhibit low color rendering index (CRI) and high correlated color temperature (CCT) due to their low emission intensity in the red region. The results showed that when Pr3+-doped CAS glasses are excited at 445 nm, red and green broadband emissions (FWHM ∼ 1300 and 1800 cm−1, respectively) with a strong dependence on the ion concentration can be observed. The (x, y) coordinates in the CIE-1931 chromaticity diagram changed from (0.61, 0.36) to (0.47, 0.41) when the Pr3+ concentration varied from 0.2 to 2.0 wt.%, what was explained in terms of cross-relaxation mechanisms between Pr3+ ions. The luminescence quantum yield (QY), in the visible range from 450 to 800 nm, of the Pr3+-doped CAS glass was determined by an integrating sphere as 0.37, which is a relatively high value for Pr3+-doped glasses. At high Pr3+ concentrations, the studied system is appropriate to be combined with other green-yellow phosphor material for white light generation.

After-glow, luminescent thermal quenching, and energy band structure of Ce-doped yttrium aluminum-gallium garnets

Yttrium aluminum-gallium garnets with cerium doped is most widely used as green-yellow phosphor in solid state lighting. Extensive research has been performed on this material concerning the luminescent thermal quenching resistance and persistent luminescence. In this paper we find that a negative correlation exists between temperature-dependent luminescence and persistent luminescence with gallium content varying. The correlation originates from the electronic structures which influence both the thermal quenching of luminescence and persistent luminescence. A detailed crystal-field calculation has been performed to understand the peak shifts. In addition, theoretical calculations reveal that oxygen vacancies provide trap levels which implement the persistent luminescence. This material could be used as potential blue-light excited persistent luminescent material, with the after-glow time up to about 1h with only cerium as the dopant, which is expected to be prolonged by co-doping other elements. This work may be helpful in guiding the discovery of other after-glow materials.

Y2Si4N6C:Ce3+ carbidonitride green-yellow phosphors: novel synthesis, photoluminescence properties, and applications

The carbidonitride Y2Si4N6C:Ce3+ green-yellow phosphor was synthesized via a novel acid-driven carbonization and carbothermal reduction nitridation method (ADC–CRN).

Self-activated luminescent material K3Dy(PO4)2: Crystal growth, structural analysis and characterizations

A potassium dysprosium orthophosphate K3Dy(PO4)2 has been prepared using high temperature flux method and structurally characterized by single crystal X-ray diffraction (SC-XRD) analysis. Its structure features a two-dimensional (2D) layer structure that is composed of [Dy(PO4)2]∞ anionic layers and K∞ cationic layers alternatively stacking along the a-axis. The diverse excitation and emission photoluminescence spectra, fluorescence lifetime and color CIE coordinates for K3Dy(PO4)2 were discussed. Although with high Dy3+ concentration, the emission spectrum excited at 350nm shows strong green-yellow emission bands corresponding to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions, respectively. The results show that K3Dy(PO4)2 can be potentially used as a green-yellow phosphor for fields of near UV-excited white-light-emitting diode and optoelectronic devices.

Nobel Prize for blue LEDs

A brief review of lighting technologies is presented. Unavoidable restrictions for incandescent light bulbs caused by the Planck distribution and properties of the human eye are illustrated. The efficiency and luminous efficacy of thermal radiation are calculated for various temperatures; the results clearly show the limitations for thermal radiators. The only way to overcome these limitations is using non-thermal radiators, such as fluorescent lamps and light-emitting diodes (LEDs). Unique advantages of LEDs undoubtedly made a revolution in this field. A crucial element of this progress is the blue LEDs (Nobel Prize 2014). Some experiments with a blue and a green LED are described: (i) the luminescence triggered in a green-yellow phosphor inside a white LED by the blue LED; (ii) radiant spectra and ‘efficiency droop’ in the LEDs; (iii) modulation of the blue LED up to 4 MHz; and (iv) the h/e ratio from the turn-on voltage of the green LED. The experiments are suitable for undergraduate laboratories and usable as classroom demonstrations.

A near-ultraviolet (NUV) converting green-yellow Ca2AlMg0.5Si1.5O7:Eu2+ phosphor for white light-emitting-diodes (w-LEDs)

Abstract Eu2+ doped aluminosilicate phosphors (Ca2AlMg0.5Si1.5O7:Eu2+ (CAMS:Eu2+)) for white near-UV w-LEDs have been synthesized by solid-state reaction at 1250 °C. The phase and crystal structure of CAMS have been analyzed by using XRD. The material with a relatively low Eu2+ concentration displayed a peak in excitation spectrum at 372 nm and a tunable emission spectrum. The colorimetric coordinate of sample with optimum Eu2+ concentration locates in green-yellow region with coordinate value of (0.2639, 0.6212). When the phosphor was pumped by UV light (λ ≈ 372 nm), we obtained bright green-yellow light, suggesting this material has a potential application as a NUV converting green-yellow phosphor for the NUV w-LEDs.

The effect of AlN and flux addition on luminescence properties of Ce doped TAG phosphor for white light emitting diodes

Abstract A series of Ce 3+ -activated Tb 3 Al 5 O 12 green-yellow phosphors were synthesized using solid state reaction method. The X-ray diffraction peaks of the synthesized phosphor were well matched to the Tb 3 Al 5 O 12 reference peak data. As the addition amount of AlN increase, the relative intensity of diffraction peak increase. But, the addition amount of AlN is over 0.3 mol, the second phase TbAlO 3 diffraction peaks increase. When the addition amount of AlN is 0.3 mol, PL shows the highest emission efficiency. These results were explained by the reducing atmosphere made using AlN. The highest emission intensity was observed when the Ce 3+ concentration is 0.25 mol. The emission intensity of the Tb 2.75 Al 5 O 12 :Ce 0.25 3+ phosphors were increased by adding BaF 2 and KNO 3 as a flux. The yellow emitting Tb 3 Al 5 O 12 :Ce 3+ phosphors obtained could be applied as white LEDs.

Combinatorial Optimization of (YxLu1−x−y)3Al5O12:Ce3y Green-Yellow Phosphors

A combinatorial chemistry method was used to synthesize and screen (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) green-yellow phosphors. The material libraries were obtained using an inkjet delivery system and screened for their fluorescence under an ultraviolet light of 365 nm. The optimized composition was identified to be (Y(0.2)Lu(0.788))(3)Al(5)O(12):Ce(3+)(0.036). Scale-up experiments confirmed that the optimized composition of the phosphor showed the highest luminescence intensity and an excellent scintillation performance with a short decay time (<60 ns). The results indicated that the (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) could be potentially useful as green-yellow phosphors for ceramic scintillators.