“…The absorption band located at around 1431 cm −1 is ascribed to the H-O-H blending vibration 42 . Furthermore, the intense absorption bands at about 837, 762, 652 and 512 cm −1 are related to the Mo-O-Mo, W-O-W, W-O and Mo-O stretching vibration modes, respectively 41,43,44 .Figure 1( a ) Representative XRD patterns of La 2 MoO 6 -La 2 WO 6 :2 x Eu 3+ ( x = 0.02, 0.06, 0.08, 0.12 and 0.16) red-emitting phosphors sintered at 850 °C. ( b ) Magnified XRD patterns in the 2θ range of 25–30.5°.…”
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
“…The absorption band located at around 1431 cm −1 is ascribed to the H-O-H blending vibration 42 . Furthermore, the intense absorption bands at about 837, 762, 652 and 512 cm −1 are related to the Mo-O-Mo, W-O-W, W-O and Mo-O stretching vibration modes, respectively 41,43,44 .Figure 1( a ) Representative XRD patterns of La 2 MoO 6 -La 2 WO 6 :2 x Eu 3+ ( x = 0.02, 0.06, 0.08, 0.12 and 0.16) red-emitting phosphors sintered at 850 °C. ( b ) Magnified XRD patterns in the 2θ range of 25–30.5°.…”
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
“…The observed specific capacitance of PVP-assisted materials (462 F g -1 ) is smaller when compared with HMTassisted materials (708 F g -1 ) [21]. However, the observed values are higher when compared with pristine Bi 2 WO 6 .…”
“…The typical synthesis of Bi 2 WO 6 is given elsewhere [21]. Briefly, stoichiometric quantities of bismuth nitrate, Bi (NO 3 ) 3 Á5H 2 O (0.4726 g) and sodium tungstate, Na 2 WO 4 (1.3903 g) were taken.…”
Section: Methodsmentioning
confidence: 99%
“…3 and WO 4 2-species reacted together to form a white colloidal Bi 2 WO 6 (Eq. 4) [21]. Consequently, the added polyvinylpyrrolidone (PVP) made the interaction between the formed colloidal Bi 2 WO 6 through hydrogen bonding [24].…”
Section: Methodsmentioning
confidence: 99%
“…The various surfactants/polymers utilized to enhance the electrochemical performance of the materials includes polyacrylic acid (PAA) [16], sodium dodecyl sulfate (SDS) [17], triton X-100 [18], polyvinyl alcohol (PVA) [19], cetyl trimethyl ammonium bromide (CTAB) [20], etc. Using this method, hexamethylenetetramine (HMT) has been used as a structure-directing agent for synthesizing Bi 2 WO 6 to obtain improved specific capacitance [21].…”
Polyvinylpyrrolidone (PVP)-assisted Bi 2 WO 6 nanoparticles were successfully synthesized by sonochemical method. Three different concentrations of PVP (0.05, 0.1, and 0.2 g) were used, and their effects over the structural, morphological, compositional, and electrochemical analysis were studied. The structural investigation revealed the formation of 100 % pure Bi 2 WO 6 phase. The presence of carbon in the PVP-assisted materials was evidenced from differential scanning calorimetry, Fourier transform infra red (FT-IR) spectroscopy and Raman analysis. There was a reduction in the particle size of Bi 2 WO 6 (30-35 nm) upon using PVP. The highly crystalline nature and the presence of carbon coating over Bi 2 WO 6 were evidenced from the high-resolution transmission electron microscopic image. Besides, the calculated d-spacing of 0.19 nm attributed to (2 0 6) lattice plane of Bi 2 WO 6 nanoparticles. Subsequently, a shift in binding energy toward larger values while using PVP was identified through X-ray photoelectron spectroscopic analysis. The electrochemical analysis showed a subsequent enhancement in specific capacitance of PVP-assisted Bi 2 WO 6 (462 F g -1 ) compared with pristine Bi 2 WO 6 (304 F g -1 ) at 3 mA cm -2 .
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