Novel red phosphors Na2CaSiO4:Eu3+ for light-emitting diodes (original) (raw)
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Synthesis and Photoluminescence Properties of the High-Brightness EU3+
2017
Eu3+ doped red phosphors Li0.5Al0.5Mg2 (MoO4)3 were prepared by the combustion method, and their luminescent properties were studied. Under the excitation of nearUV 395 nm, the phosphors show intense red emission with the peaks located at 615 and 595 nm. The influence of Eu3+ concentration on the luminescent properties of Eu3+ doped Li0.5Al0.5Mg2(MoO4)3 was investigated and the 3% (mole fraction) was the appropriate molar concentration. By sintering Li0.5Al0.5Mg2(MoO4)3:xEu3+ phosphor at 750°C, PL intensity has a maximum value at 615 nm with Commision Internationale de I’Eclairage 1931 (CIE 1931) chromaticity coordinates (0.6616, 0.3336) . The phosphor could be suitable for the application of white light-emitting diodes.
Applied Physics Letters
White light emitting diodes (LEDs) composed of a blue LED and a green/yellow downconverter material (phosphor) can be very efficient, but the color is often not considered very pleasant. Although the color rendering can be improved by adding a second, red-emitting phosphor, this generally results in significantly reduced efficacy of the device due to the broad emission of available conventional red-emitting phosphors. Trivalent europium is well-known for its characteristic narrow-band emission in the red region, with little radiation outside the eye sensitivity area, making it an ideal candidate for enabling high color quality as well as a high lumen equivalent of radiation from a spectrum point of view. However, a thorough study of the practical potential and challenges of Eu 3þ as a red emitter for white LEDs has remained elusive so far due to the low excitation probability in the blue spectral range which is often even considered a fundamental limitation. Here, we show that the absorption in the blue region can be brought into an interesting regime for white LEDs and show that it is possible to increase both the color rendering and efficacy simultaneously using Eu 3þ as a red emitter, compared to warm white LEDs comprising conventional materials.
Luminescence and luminescence quenching of highly efficient Y2Mo4O15:Eu3+ phosphors and ceramics
Scientific Reports, 2016
A good LED phosphor must possess strong enough absorption, high quantum yields, colour purity, and quenching temperatures. Our synthesized Y 2 Mo 4 O 15 :Eu 3+ phosphors possess all of these properties. Excitation of these materials with near-UV or blue radiation yields bright red emission and the colour coordinates are relatively stable upon temperature increase. Furthermore, samples doped with 50% Eu 3+ showed quantum yields up to 85%, what is suitable for commercial application. Temperature dependent emission spectra revealed that heavily Eu 3+ doped phosphors possess stable emission up to 400 K and lose half of the efficiency only at 515 K. In addition, ceramic disks of Y 2 Mo 4 O 15 :75%Eu 3+ phosphor with thickness of 0.71 and 0.98 mm were prepared and it turned out that they efficiently convert radiation of 375 and 400 nm LEDs to the red light, whereas combination with 455 nm LED yields purple colour. Solid state light sources based on the blue emitting InGaN semiconductor chips became a revolution in lighting industry after the discovery of efficient blue emitting diode by S. Nakamura in 1991 1. However, the blend of the blue light emitted by diode and yellow emitted by a Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) phosphor usually yields a cold white light due to deficiency of the red component in the spectrum. To overcome this issue some red phosphors are added to the light source. Frequently used nitride based red phosphors are very expensive and require complicated synthesis techniques. Another way to produce solid state white light sources is to employ near UV emitting LED chip and coat it with red, green and blue phosphor. The advantage of such approach is much broader phosphor selection than for blue LED excitation. Inorganic materials doped with rare earth ions are mostly used as activators in the mentioned phosphors. Since there are some efficient blue (BaMgAl 10 O 17 :Eu 2+) and green (SrSi 2 O 2 N 2 :Eu 2+ , Ba 2 SiO 4 :Eu 2+) 2,3 phosphors, the main problems arise with finding a suitable and relatively inexpensive red-emitting phosphor. Moreover, the requirements for LED phosphors are also high, for instance, strong absorption of LED radiation, high thermal quenching temperature, high quantum yield, excellent chemical and thermal stability and absence of emission saturation at high fluxes 4. Unfortunately, it is very hard to find materials that meet all the aforementioned criteria and, therefore, the reports of efficient Eu 3+ doped phosphors with high thermal stability is scarce. Trivalent europium doped materials are usually considered as good red-emitting phosphor candidates for LEDs. On the other hand, Eu 3+ ions typically possess rather low absorption strength due to the spin and parity forbidden nature of their intraconfigurational [Xe]4f 6 → [Xe]4f 6 transitions 5. However, in molybdates, tungstates, niobates and vanadates these transitions, especially at shorter wavelengths (< 400 nm), become rather strong due to admixing with low lying charge transfer (CT) band 6-8. The position of the CT band depends on the host material as do the emission spectra of Eu 3+ ions. Thus by selecting the appropriate host material one should be able to obtain a desired absorption strength and emission profile.
Eu3+-activated potential red-emitting phosphor for solid-state lighting
Optik, 2017
The intense red-emitting NaCaY0.2Eu0.8(MoO4)3 phosphor was prepared by using a sol-gel method for the first time. Thermogravimetric-diferential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, FT-IR and luminescent measurements were used to characterize the NaCaY0.2Eu0.8(MoO4)3 particles. The resulting products obtained by using the sol-gel method have a narrower size distribution and a more regular particle shape than those obtained by using the solid-state reaction. The spectra analysis indicated that the obtained phosphor could be excited by UV light of 395 nm and visible light of 466 nm, also emits intense red light with a maximum at about 614 nm. The luminescent intensity of sol-gel derived is comparable with the solid state product and it is about 84 % of solid-state product under 395 nm light excitation. Comparative study with YAG:Ce and CaS:Eu 2+ phosphors, suggested that our synthesized phosphor can be used as an efficient red-emitting phosphor to compensate the red deficiency of YAG:Ce phosphor and also can serve as an alternative phosphor to replace sulfide based phosphors in the solid-state lighting applications.
Journal of Alloys and Compounds, 2012
Rare-earth ions doped inorganic luminescent materials (phosphors) in nanodimensions find widespread scientific and industrial applications. This paper report a novel red-emitting Eu 3+ doped Ba 3 Ca 3 (PO 4) 4 phosphors in nanodimensions were synthesized via one-step conventional solid state reaction method for first time at high temperature in air atmosphere. The morphology and nanostructures of synthesized phosphors were determined by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray spectroscopy (EDS). The XRD observation reveals that the undoped and Eu 3+ doped Ba 3 Ca 3 (PO 4) 4 phosphors are in single crystalline phase with the sizes of 40-65 nm. FE-SEM image indicated the phosphor is composed of nearly spherical particles and rod like structures with several nanometer sizes. The presence of orthophosphates in Ba 3 Ca 3 (PO 4) 4 phosphor was identified by Fourier transform infrared (FT-IR) analysis and the thermal stability was studied by Differential scanning calorimetry (DSC). Diffuse reflectance spectra (DRS) evidenced the incorporated Eu 3+ ions in host material. In addition, the bandgap of these samples were estimated from the Mubelka-Munk function. The room-temperature photoluminescence spectra show the characteristic red fluorescence originating from intra 4f 5 D 0 ? 7 F 2 (616 nm) transition of Eu 3+ is observed by introducing Eu 3+ ions in Ba 3 Ca 3 (PO 4) 4 phosphors. The calculated color coordinates are lies in the orange-red region. Therefore, these obtained results suggest that the prepared phosphors exhibit great potential for use as red-component for near ultraviolet white light emitting diodes (NUV WLEDs).
Eu 2 + luminescence in the EuAl 2 O 4 concentrated phosphor
Radiation Measurements, 2007
Powder samples of EuAl 2 O 4 and (Eu, Sr)Al 2 O 4 with a quantum efficiency (QE) of the Eu 2+ emission more than 0.30 were synthesized. A modified method of QE determination is described and results of the QE measurements for EuAl 2 O 4 , (Eu 0.8 Sr 0.2 )Al 2 O 4 , (Eu 0.65 Sr 0.35 )Al 2 O 4 , and a diluted sample (Sr 0.98 Eu 0.02 )Al 2 O 4 are presented. Excitation and emission spectra as well as decay behaviour of the Eu 2+ luminescence in (Eu 1−x Sr x )Al 2 O 4 in the temperature region of 20-300 K are studied. It is concluded that the main reason for the high QE is a pronounced relaxation of the crystal lattice after excitation of the Eu 2+ ions resulting in an emission with a large Stokes shift and, therefore, in a restriction of energy migration. Eu ions occupying the crystallographic sites with the higher coordination number (Eu II ) are supposed to be the luminescence centres in (EuSr)Al 2 O 4 lattice.
Alkali earth sulfide phosphors doped with Eu2+ and Ce3+ for LEDs
Optical Materials, 2007
CaS:Eu 2+ , SrS:Eu 2+ , CaS:Ce 3+ , SrS:Ce 3+ , CaS:Eu 2+ , Ce 3+ and SrS:Eu 2+ , Ce 3+ phosphor samples have been prepared using a solid state chemical reaction method. Emission and excitation spectra of the samples are investigated. SrS:Ce 3+ , CaS:Ce 3+ , SrS:Eu 2+ and CaS:Eu 2+ emit greenish blue (482 nm), green (515 nm), orange (606 nm), and red (648 nm) light, respectively. For the co-doped samples, SrS:Eu 2+ , Ce 3+ and CaS:Eu 2+ , Ce 3+ , energy transfer from Ce 3+ to Eu 2+ is observed. Ce 3+ emission has been totally quenched because of the energy transfer. Eu 2+ emissions are estimated to be enhanced by 28% and 18% in SrS and CaS hosts, respectively, at the present doping concentration. The samples are also excited by blue light emitting diodes (450 nm) to exam them as potential coating phosphors for the diodes.
Eu2+Eu2+ luminescence in the EuAl2O4EuAl2O4 concentrated phosphor
Radiation Measurements, 2007
Powder samples of EuAl 2 O 4 and (Eu, Sr)Al 2 O 4 with a quantum efficiency (QE) of the Eu 2+ emission more than 0.30 were synthesized. A modified method of QE determination is described and results of the QE measurements for EuAl 2 O 4 , (Eu 0.8 Sr 0.2 )Al 2 O 4 , (Eu 0.65 Sr 0.35 )Al 2 O 4 , and a diluted sample (Sr 0.98 Eu 0.02 )Al 2 O 4 are presented. Excitation and emission spectra as well as decay behaviour of the Eu 2+ luminescence in (Eu 1−x Sr x )Al 2 O 4 in the temperature region of 20-300 K are studied. It is concluded that the main reason for the high QE is a pronounced relaxation of the crystal lattice after excitation of the Eu 2+ ions resulting in an emission with a large Stokes shift and, therefore, in a restriction of energy migration. Eu ions occupying the crystallographic sites with the higher coordination number (Eu II ) are supposed to be the luminescence centres in (EuSr)Al 2 O 4 lattice.
Emission color variation of (Ba,Sr)_3BP_3O_12:Eu^2+ phosphors for white light LEDs
Optics Express, 2010
A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, were synthesized by a solid state reaction. Two emission bands at 465 nm and 520 nm were attributed to the f-d transitions of doped Eu 2+ ions occupying in two different cation sites in host lattices and emission color variation was observed by substituting the M 2+ sites, which was rationalized in terms of two competing factors of the crystal field strength and bond covalence. Green and bluish-white pc-LEDs were fabricated by combination of a 370 nm near-UV chip and composition-optimized Ba 3 BP 3 O 12 :Eu 2+ and (Ba,Sr) 3 BP 3 O 12 :Eu 2+ phosphors, respectively. The series of phosphors may serve as a promising green and bluish-white luminescent materials used in fabrication of near UV-based white pc-LEDs.
Journal of the American Chemical Society
In this work, we present a computational protocol that is able to predict the experimental absorption and emission spectral shapes of Eu 2+doped phosphors. The protocol is based on time-dependent density functional theory and operates in conjunction with an excited-state dynamics approach. It is demonstrated that across the study set consisting of representative examples of nitride, oxo-nitride, and oxide Eu 2+-doped phosphors, the energy distribution and the band shape of the emission spectrum are related to the nature of the 4f−5d transitions that are probed in the absorption process. Since the 4f orbitals are very nearly nonbonding, the decisive quantity is the covalency of the 5d acceptor orbitals that become populated in the electronically excited state that leads to emission. The stronger the (anti) bonding interaction between the lanthanide and the ligands is in the excited state, the larger will be the excited state distortion. Consequently, the corresponding emission will get broader due to the vibronic progression that is induced by the structural distortion. In addition, the energy separation of the absorption bands that are dominated by states with valence 4f−5d and a metal to ligand charge transfer character defines a measure for the thermal quenching of the studied Eu 2+-doped phosphors. Based on this analysis, simple descriptors are identified that show a strong correlation with the energy position and bandwidth of the experimental emission bands without the need for elaborate calculations. Overall, we believe that this study serves as an important reference for designing new Eu 2+-doped phosphors with desired photoluminescence properties.