Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

Abstract

A series of novel Eu3+ -activated La 2 MoO 6 -La 2 WO 6 red-emitting phosphors have been successfully prepared by a citrate-assisted sol-gel process. Both photoluminescence excitation and emission spectra suggest that the resultant products have the strong ultrabroad absorption band ranging from 220 to 450 nm. Under the excitation of 379 nm, the characteristic emissions of Eu 3+ ions corresponding to the 5 D 0 → 7 F J transitions are observed in the doped samples. The optimal doping concentration for Eu 3+ions is found to be 12 mol% and the quenching mechanism is attributed to the dipole-dipole interaction. A theoretical calculation based on the Judd-Ofelt theory is carried out to explore the local structure environment around the Eu 3+ ions. The studied samples exhibit a typical thermal quenching effect with a T 0.5 value of 338 K and the activation energy is determined to be 0.427 eV. A near-ultraviolet (NUV)-based white light-emitting diode (LED) is packaged by integrating a mixture of resultant phosphors, commercial blue-emitting and green-emitting phosphors into an NUV LED chip. The fabricated LED device emits glaring white light with high color rendering index (84.6) and proper correlated color temperature (6492 K). These results demonstrate that the Eu 3+ -activated La 2 MoO 6 -La 2 WO 6 compounds are a promising candidate for indoor lighting as red-emitting phosphors.By virtue of admirable advantages of long working lifetime, energy saving, low cost, high luminous efficiency and environmental compatibility, the phosphor-converted white light-emitting diodes (WLEDs) which are considered as the next-generation illumination sources to supersede the conventional fluorescent lamps have been extensively used in indoor lighting, automobile displays and flashlights [1][2][3][4][5] . Presently, the commercial WLEDs which are made up of a blue-emitting InGaN LED chip and Y 3 Al 5 O 12 :Ce 3+ yellow-emitting phosphors suffer from poor color rending index (CRI ~ 70-80) and high correlated color temperature (CCT ~ 7000 K) as a result of inefficient red emission component [6][7][8] . To circumvent these drawbacks, a new strategy utilizing the near-ultraviolet (NUV) LED chip to pump the hybrid tricolor (blue, green and red) phosphors is performed to emit warm white light [9][10][11] . From the aforementioned combinations, one knows that the eventual behaviors of WLED devices can be significantly affected by the phosphors and they are expected to be efficiently excited by NUV or blue light. In comparison with commercial blue-emitting and green-emitting phosphors, the current red-emitting phosphors, by taking Y 2 O 2 S:Eu 3+ for example, still exhibit some unsatisfied characteristics such as weak absorption in the NUV/blue region, low luminous efficiency and poor stability 12,13 . In order to improve the performance of red-emitting phosphors, the nitride-and germanide-based red-emitting phosphors, such as Ca 2 Si 5 N 8 :Eu 2+ , Sr[LiAl 3 N 4 ]:Eu

Optical Properties of Red-Emitting Rb2Bi(PO4)(MoO4):Eu3+ Powders and Ceramics with High Quantum Efficiency for White LEDs

“…This observation indicates that Eu 3+ ions occupy non-centrosymmetric lattice site in the Rb 2 Bi(PO 4 )(MoO 4 ) host matrix. On the other hand, the intensity difference between MD and ED transitions is rather low if compared to some other molybdate host matrices doped with Eu 3+ ions, for instance, Li 3 Ba 2 La 3 (MoO 4 ):Eu 3+ [31], Tb 2 Mo 3 O 12 :Eu 3+ [18], La 2 MoO 6 :Eu 3+ [32], LiEuMo 2 O 8 [33], La 2 Mo 2 O 9 :Eu 3+ [34] and so on. The rather small difference between ED and MD transitions of Eu 3+ ions in Rb 2 Bi(PO 4 )(MoO 4 ) host matrix can be assigned to relatively symmetric dodecahedral BiO 8 site, which is occupied by Eu 3+ .…”

A novel dazzling Eu3+‐doped whitlockite‐type phosphate red‐emitting phosphor for white light‐emitting diodes

“…The potential of our phosphors for the preparation of near‐ultraviolet and blue excited white LEDs for display device applications was investigated by integrating a NUV LED chip and a blending of synthesized red‐emitting phosphors, commercial (Sr,Ba) 2 SiO 4 : Eu 2+ green‐emitting and BaMgAl 10 O 17 : Eu 2+ (BAM: Eu 2+ ) blue‐emitting phosphors to fabricate a white LED device . Its electroluminescent (EL) emission spectrum of the fabricated WLED device, driving by a forward bias current of 120 mA, is shown in Figure A.…”

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

“…Because of the 7 F 2 energy level splits, the 5 D 0 → 7 F 2 electron transition shows α ‐ 7 F 2 and β ‐ 7 F 2 peaks 14,15 . The α ‐ 7 F 2 and β ‐ 7 F 2 peaks move to both sides, which indicates that the energy of crystal field splitting is gradually increased.…”

“…But so far, it mostly stays in the preparation of the rare earth ions‐doped La 2 MoO 6 phosphors with a single element. There are few reports on the preparation of La 2 MoO 6 phosphors by co‐doping different ions 13‐16 . In many reports, the co‐doped Bi 3+ ions can effectively enhance the luminescence performance of phosphors by the action of a sensitizer, such as CaMoO 4 :Bi 3+ , Eu 3+ , CaY 4 (SiO 4 ) 3 O:Bi 3+ , Eu 3+ and BaLa 2 Si 3 O 10 :Eu 3+ , Bi 3+ phosphors 17‐19 .…”