On the stability and reliability of Sr_1-xBa_xSi_2O_2N_2:Eu^2+ phosphors for white LED applications

Cho, I. H.; Anoop, Gopinathan; Suh, Dong Wook; Lee, S. J.; Yoo, J. S.

doi:10.1364/ome.2.001292

Cited by 48 publications

(32 citation statements)

References 49 publications

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“…The resulting combination of yellow light with the residual blue light produces white light as perceived by the human eye12345. These phosphors should efficiently down-convert the blue photon and should maintain good optical performance even at an elevated ambient temperature.…”

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confidence: 99%

“…Even though GaN/InGaN-based LEDs have a very long lifetime (~50,000–100,000 h), the light emission from phosphor-converted LEDs (pcLEDs) degrades over time with an average lifetime of only about 7000–9000 h. The major reasons for the degradation of pcLEDs are emission intensity reduction from phosphors, which is predominantly due to thermal quenching, and thermal degradation6. Thermal quenching of luminescence is the result of excess heat at the p-n junction, which results in an increase in the probability of non-radiative transitions and consequently degrades the efficiency of the phosphor24. Thermal degradation results from the thermal/photo oxidation of activator ions in the phosphor24.…”

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confidence: 99%

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Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes

Anoop

Rani

Lim

et al. 2016

Sci Rep

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The long-term instability of the presently available best commercial phosphor-converted light-emitting diodes (pcLEDs) is the most serious obstacle for the realization of low-cost and energy-saving lighting applications. Emission from pcLEDs starts to degrade after approximately 200 h of operation because of thermal degradation of the phosphors. We propose a new strategy to overcome this thermal degradation problem of phosphors by wrapping the phosphor particles with reduced graphene oxide (rGO). Through the rGO wrapping, we have succeeded in controlling the thermal degradation of phosphors and improving the stability of fabricated pcLEDs. We have fabricated pcLEDs with long-term stability that maintain nearly 98% of their initial luminescence emission intensity even after 800 h of continuous operation at 85 °C and 85% relative humidity. The pcLEDs fabricated using SrBaSi2O2N2:Eu2+ phosphor particles wrapped with reduced graphene oxide are thermally stable because of enhanced heat dissipation that prevents the ionization of Eu2+ to Eu3+. We believe that this technique can be applied to other rare-earth doped phosphors for the realization of highly efficient and stable white LEDs.

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confidence: 99%

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confidence: 99%

Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes

Anoop

Rani

Lim

et al. 2016

Sci Rep

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“…The 537 nm peak in the GP70 and GP180 films is from the 4f 6 5d → 4f 7 transitions in Eu 2+ of the phosphor. 11,12 The GO−phosphor hybrid films show shoulder peaks at ∼500 nm (for GP70) and 510 nm (for GP180), which correspond to π−π* gap values of ∼2.56 and 2.43 eV, respectively. The origin of these emission peaks from the GO−phosphor hybrid films is discussed later.…”

Section: Resultsmentioning

confidence: 99%

Graphene Oxide–Phosphor Hybrid Nanoscrolls with High Luminescent Quantum Yield: Synthesis, Structural, and X-ray Absorption Studies

Rani¹,

Oh²,

Woo³

et al. 2015

ACS Appl. Mater. Interfaces

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Highly luminescent graphene oxide (GO)-phosphor hybrid thin films with a maximum quantum yield of 9.6% were synthesized via a simple chemical method. An intense luminescence emission peak at 537 nm and a broad emission peak at 400 nm were observed from the GO-phosphor hybrid films. The maximum quantum yield of the emissions from the hybrid films was found to be 9.6%, which is 48 times higher than that of pristine GO films. The GO-phosphor hybrids were prepared via spin-coating and subsequent postannealing of the films, resulting in scrolling of the GO sheets. The resulting GO nanoscrolls exhibited a length of ∼2 μm with nanoscale interior cavities. Transmission electron microscopy and selected-area electron diffraction analyses revealed that the lattice structure of the tubular scrolls is similar to that of carbon nanotubes. While pristine GO films are p-type, in the GO-phosphor hybrids, the Fermi level shifted upward and fell between the HOMO-LUMO gap due to phosphor attachment via C-N bonding. The highly luminescent GO-phosphor hybrids will find important applications in graphene-based optoelectronic devices.

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“…Phosphors luminescence is impacted by temperature and thermal quenching effects are known to degrade luminescence efficiency [20,21]. Thermal management is one of the biggest issues in high power white pcLED packages.…”

Section: Temperature Stability Measurementsmentioning

confidence: 99%

Optical efficiency characterization of LED phosphors using a double integrating sphere system

2015

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We report on the methodology and implementation of a robust and accurate double integrating sphere system for measuring the absolute photoluminescence quantum yield and its temperature dependence of commercially available phosphors (garnets, silicates and nitrides). The potential of our instrument for the examination of light interaction with samples of different absorption and diffusion coefficients is also presented, as optical properties of luminescent materials have a major impact on the efficiency of LED's packaging. Our work gives special attention to the control and the optimization of light losses in the optical system in order to ensure reliable measurements. The YAG:Ce phosphor shows the highest luminescence quantum yield at 97% efficiency, the green silicate the lowest with 79% efficiency. Silicate phosphors show up to 15% loss of luminescence intensity when temperature is raised to 140°C.

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On the stability and reliability of Sr_1-xBa_xSi_2O_2N_2:Eu^2+ phosphors for white LED applications

Cited by 48 publications

References 49 publications

Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes

Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes

Graphene Oxide–Phosphor Hybrid Nanoscrolls with High Luminescent Quantum Yield: Synthesis, Structural, and X-ray Absorption Studies

Optical efficiency characterization of LED phosphors using a double integrating sphere system

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