Rare earth-free high color rendering white light-emitting diodes using CsVO<sub>3</sub> with highest quantum efficiency for vanadate phosphors

Nakajima, Tomohiko; Isobe, Masahiko; Uzawa, Yuko; Tsuchiya, Toshio

doi:10.1039/c5tc01929j

Cited by 50 publications

(22 citation statements)

References 51 publications

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“…In some of the vanadate compounds, an unusual luminescent property was observed, i.e., a broad and intense charge transfer (CT) band due to the charge transfer from O 2− ligand anion to V 5+ in the NUV range, thereby yielding a broad emission band over the entire visible range (400–700 nm)3637. Furthermore, these materials have considerable advantages over conventional phosphor materials, including low cost and energy efficiency (due to low calcination temperature) as well as broadband emission to obtain high CRI3839.…”

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confidence: 99%

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Bharat

Jeon²,

Krishna

et al. 2017

Sci Rep

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The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.

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confidence: 99%

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Bharat

Jeon²,

Krishna

et al. 2017

Sci Rep

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“…The external quantum efficiency (EQE) can be calculated using the formula η o = N em /N exc × 100%, where N em and N exc are the number of emitted and excited photons, respectively. The internal quantum efficiency (IQE) can be calculated from η i = N em /N abs × 100%, where N abs is the number of absorbed photons40. The EQE and IQE for Sr 1.94 Ce 0.06 Si 5 N 8 phosphors were calculated to be 51% and 71%, respectively.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via efficient chemical vapor deposition

Yang

Som

Das

et al. 2017

Sci Rep

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Novel chemical vapor deposition (CVD) process was successfully developed for the growth of Sr2Si5N8:Ce3+ phosphors with elevated luminescent properties. Metallic strontium was used as a vapor source for producing Sr3N2 vapor to react with Si3N4 powder via a homogeneous gas-solid reaction. The phosphors prepared via the CVD process showed high crystallinity, homogeneous particle size ranging from 8 to 10 μm, and high luminescence properties. In contrast, the phosphors prepared via the conventional solid-state reaction process exhibited relative low crystallinity, non-uniform particle size in the range of 0.5–5 μm and relatively lower luminescent properties than the phosphors synthesized via the CVD process. Upon the blue light excitation, Sr2−xCexSi5N8 phosphors exhibited a broad yellow band. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions from x = 0.02 to x = 0.10. The maximum emission was observed at x = 0.06, and the external and internal quantum efficiencies were calculated to be 51% and 71%, respectively. Furthermore, the CVD derived optimum Sr1.94Ce0.06Si5N8 phosphor exhibited sufficient thermal stability for blue-LEDs and the activation energy was calculated to be 0.33 eV. The results demonstrate a potential synthesis process for nitride phosphors suitable for light emitting diodes.

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“…Figure A illustrates the luminescence spectra of BaSO 4 and Sr 1.906 Ce 0.06 Eu 0.004 Si 5 N 8 under blue excitation at 460 nm. The external quantum efficiency of Sr 1.906 Ce 0.06 Eu 0.004 Si 5 N 8 was measured to be 54%, while the internal quantum efficiency was found to be 70% …”

Section: Resultsmentioning

confidence: 95%

“…The integral represents the spectral overlap. The critical distance ( R c ) involved in energy transfer from Ce 3+ ions to Eu 2+ ions is defined as the distance at which the probability of energy transfer equals the probability of radiative emission from Ce 3+ ions, that is, the distance where P Ce‐Eu (dd) = 1/ τ s and hence,

R_{c}^{6} = 0.63 \times 10^{28} \frac{4.8 \times 10^{- 16} f_{d}}{E^{4}} \int F_{S} false(E false) F_{A} false(E false) d E

…”

Section: Resultsmentioning

confidence: 99%

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

Yang

Som

et al. 2018

J Am Ceram Soc

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A modified chemical vapor deposition (CVD) technique is used to synthesize the color‐tunable siliconitride Sr2‐1.5x‐yCexEuySi5N8 (x = 0.000‐0.016 and y = 0.000‐0.020) phosphors. In comparison with the conventional solid‐state method, the CVD approach successfully improved the crystallinity, particle size distribution, and photoluminescence through the enhanced gas‐solid reaction. Under blue excitation, Sr1.98Eu0.02Si5N8 exhibited a red emission band at 618 nm. The incorporation of Ce3+ ions increased the emission intensity of Eu2+ ions by approximately 10% owing to the enhanced absorption and dipole‐dipole energy transfer process from Ce3+ to Eu2+ ions. It resulted in a shift of the emission colors from yellow to red region. The external and internal quantum efficiencies of Sr1.906Ce0.06Eu0.004Si5N8 were calculated as 54% and 70%, respectively. The activation energy of thermal stability for Sr1.906Ce0.06Eu0.004Si5N8 was evaluated as 0.31 eV. A white LED with a color rendering index of 80 and a CCT of 4964 K was successfully fabricated with the present phosphors. The current research demonstrated a new series of Sr2Si5N8:Ce3+, Eu2+ phosphors with color‐tunability for fabricating white LEDs with high color‐rendering index.

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Rare earth-free high color rendering white light-emitting diodes using CsVO₃ with highest quantum efficiency for vanadate phosphors

Abstract: Internal quantum efficiency of CsVO3 was considerably enhanced up to 95.8%, and a rare earth free white LED that had a very high color rendering index of 91.1 was realized by using CsVO3 and a deep red phosphor Mg2TiO4:Mn4+.

Cited by 50 publications

References 51 publications

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via efficient chemical vapor deposition

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

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Rare earth-free high color rendering white light-emitting diodes using CsVO3 with highest quantum efficiency for vanadate phosphors

Abstract: Internal quantum efficiency of CsVO3 was considerably enhanced up to 95.8%, and a rare earth free white LED that had a very high color rendering index of 91.1 was realized by using CsVO3 and a deep red phosphor Mg2TiO4:Mn4+.

Cited by 50 publications

References 51 publications

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via efficient chemical vapor deposition

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

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Rare earth-free high color rendering white light-emitting diodes using CsVO₃ with highest quantum efficiency for vanadate phosphors