Novel Ba–Sc–Si-oxide and oxynitride phosphors for white LED
Introduction
White LEDs are widely anticipated for use in new energy-saving lighting systems to solve environmental problems in the near future. The blue-emitting InGaN-based white LED is the major lighting component. The most dominant white LEDs use a blue-emitting LED that excites a yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor dispersed in epoxy resin on a blue LED chip [1]. The white light is produced by mixing the blue and yellow light. This method is presently the most efficient among available techniques. However, the color is not true white because of lacking red and green color component. Therefore, for use in a white LED, it is necessary to identify a novel phosphor that can cover for lacking color and excited by blue light.
Promising materials for use in a white LED phosphor are silicates and alkaline earth silicon oxynitride doped with Eu2+ [2]. These hosts of phosphor with various crystal structure and high stability have excellent luminescence properties for use in white LEDs. In particular, Eu2+-doped alkaline earth silicon oxynitrides present the advantage of being excited by blue light because of strong covalency of its host materials [3].
In this study, we report the luminescence properties of novel alkaline earth silicon oxide Ba9Sc2Si6O24:Eu2+ and alkaline earth silicon oxynitride Ba9Sc2+δSi6O24−3δN3δ:Eu2+ phosphors for use in white LEDs.
The Ba9Sc2Si6O24:Eu2+ phosphors have broad absorption of blue light (ca. 450 nm) by the allowed 4f–5d transition. These phosphors emit at about 460 and 580 nm, depending on the coordination number and symmetry of emission ion sites in the host lattice. The 4f65d energy level of the emission ion Eu2+ has a wide distribution of the electron orbital. The excited state is affected by strong crystal fields and distorted coordination. Consequently, the energy gap separating the ground state 8S and the bottom of 4f65d level of Eu2+ component becomes smaller than that of other oxide host materials because the 4f65d energy level is split by the increased crystal field strength. Therefore, the luminescence wavelength shifts to the longer wavelength side [4], [5], [6].
The Ba9Sc2+δSi6O24−3δN3δ:Eu2+ phosphors are excited by the blue light. The Ba9Sc2+δSi6O24−3δN3δ:Eu2+ phosphors show yellow emissions of 530–650 nm after the nitrization samples shift to the longer wavelength side because of the increased crystal field splitting and covalency [7].
Section snippets
Experimental
Ba9Sc2Si6O24:Eu2+ and Ba9Sc2+δSi6O24−3δN3δ:Eu2+ were synthesized using a solid-state reaction method. As raw materials, BaCO3 (Kanto Chemical Co., Inc. 3N), Sc2O3 (Shin-Etsu Chemical, Co., Inc. 4N), SiO2 (Kanto Chemical Co., Inc. 3N), and Eu2O3 (Shin-Etsu Chemical Co., Inc., 4N) were used.
In oxide Ba9Sc2Si6O24:Eu2+, a stoichiometric mixture was fired in an alumina crucible at 1573–1773 K for 12 h in air. The samples after firing were ground and fired in an alumina boat at 1573–1773 K for 12 h under
Ba9Sc2Si6O24:Eu2+
The crystal structure and coordination of Ba9Sc2Si6O24 are presented in Fig. 1(a) and (b) and Fig. 2 [8]. The structure closely resembles that of Ba-merwinite in the linkage of [SiO4] tetrahedral and [ScO6] octahedral. Three different Ba sites exist in this structure. The coordinations of the Ba2+ are 9-, 10- and 12-fold and the bond length is irregular. The XRD patterns, excitation and emission spectra of (Ba1−xEux)9Sc2Si6O24 are shown, respectively, in Fig. 3, Fig. 4. Samples were obtained in
Conclusion
For this study, Eu2+-activated Ba9Sc2Si6O24 and BaSc2+δSi6O24−3δN3δ were synthesized. They were characterized using X-ray powder diffraction, excitation, and emission spectroscopy. For excitation in the UV–blue range, Ba9Sc2Si6O24:Eu2+ exhibits efficient green emission at 508 nm, whereas yellow emission at 570 nm was found for Ba9Sc2+δSi6O24−3δN3δ:Eu2+. By virtue of their intense absorption and excitation band in the UV–blue spectral region (370–460 nm), these materials are inferred to be useful
Acknowledgement
This work was supported by the project of Center for Transdisciplinary Research, Niigata University.
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2022, Optical MaterialsCitation Excerpt :In this type of lighting device, the phosphor is one of key subassemblies, which absorbs the energy of the light generated by the LED chips and transfers it into the light with different colors. In various phosphors, the roles of the luminescence centers are widely acted as by the rare earth ions, such as Ce3+ [1–3], Eu2+ [4–6], Eu3+ [7,8], Tb3+ [8,9] and Dy3+ [10,11]. And some non-rare earth ions, such as Bi3+ [12,13], Mn2+ [14,15], Mn4+ [16,17] and Cr3+ [18,19], are paid more and more attention for applying as the luminescence centers in the phosphors because of the scarcity and exorbitant price of the rare earth ions.
Luminescent-center tuning for Ba<inf>6</inf>Ca<inf>3</inf>YAlSi<inf>6</inf>O<inf>24</inf>:Ce<sup>3+</sup>, Na<sup>+</sup> orthosilicate phosphors
2019, Journal of Alloys and CompoundsThe cyan-green luminescent behaviour of nitrided Ba<inf>9</inf>Y<inf>2</inf>Si<inf>6</inf>O<inf>24</inf>: Eu<sup>2+</sup> phosphors for W-LED
2018, Ceramics InternationalCitation Excerpt :When the temperature rises to 180 °C, there was a serious thermal quenching. However, the thermal stability of the sample after nitriding was significantly higher than that of the Ba9M2Si6O24: Eu2+ (M=Sc, Y) phosphor [12,16]. It is indicated that the addition of N3- can improve the thermal stability of Ba9Y2Si6O24: Eu2+ phosphors, which is mainly attributed to the stronger covalent rigidity of Si-N bonds than that of Si-O bonds.
Crystal-site engineering for developing tunable green light emitting Ba<inf>9</inf>Lu<inf>2</inf>Si<inf>6</inf>O<inf>24</inf>:Eu<sup>2+</sup> phosphors for efficient white LEDs
2018, Journal of Alloys and CompoundsCitation Excerpt :Among phosphor candidates, increasing interest has recently been expressed in Ba9Re2Si6O24 (Re = Sc, Y, Lu) (abbreviated as BSSO) [42,43]. Nakano et al. reported that BSSO doped with Eu2+ shows efficient green and blue emission under UV and near UV light excitation [44]. The Eu2+ doped Ba9Sc2Si6O24 and Ba9Y2Si6O24 phosphors emit efficient green light under UV and near UV light irradiation [44,45].