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

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


(a) Schematic illustration showing experimental method of GO wrapping over phosphor. (b) Digital image of the fabricated pcLED using GO 1200 phosphor operated at 100 mA. (c–e) FESEM images of fresh phosphor and phosphor samples GO 1200, and GO 1350. (f) PL of the fresh, annealed, and GO-wrapped phosphors. Inset shows the variation in PL intensity with annealing and GO wrapping. (g) XRD patterns of fresh, annealed, and GO-wrapped phosphors.
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f1: (a) Schematic illustration showing experimental method of GO wrapping over phosphor. (b) Digital image of the fabricated pcLED using GO 1200 phosphor operated at 100 mA. (c–e) FESEM images of fresh phosphor and phosphor samples GO 1200, and GO 1350. (f) PL of the fresh, annealed, and GO-wrapped phosphors. Inset shows the variation in PL intensity with annealing and GO wrapping. (g) XRD patterns of fresh, annealed, and GO-wrapped phosphors.

Mentions: The rGO wrapping was achieved through mixing appropriate amount of GO and phosphor followed by a calcination at temperatures of 700 °C, 1200 °C, and 1350 °C for 6 h in a reducing (N2/H2) atmosphere. The annealing of GO-phosphor composite results in a wrapping of rGO around the phosphor particles. Figure 1(a) shows a schematic illustration of the synthesis of rGO wrapped phosphor. The samples of unwrapped phosphors annealed at 700, 1200 and 1350 °C are labelled as UW 700, UW 1200 and UW 1350 while those annealed with GO are labeled as GO 700, GO 1200 and GO 1350 respectively. Figure 1(b) shows digital image of the pcLED operated at 100 mA current.


Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes
(a) Schematic illustration showing experimental method of GO wrapping over phosphor. (b) Digital image of the fabricated pcLED using GO 1200 phosphor operated at 100 mA. (c–e) FESEM images of fresh phosphor and phosphor samples GO 1200, and GO 1350. (f) PL of the fresh, annealed, and GO-wrapped phosphors. Inset shows the variation in PL intensity with annealing and GO wrapping. (g) XRD patterns of fresh, annealed, and GO-wrapped phosphors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037423&req=5

f1: (a) Schematic illustration showing experimental method of GO wrapping over phosphor. (b) Digital image of the fabricated pcLED using GO 1200 phosphor operated at 100 mA. (c–e) FESEM images of fresh phosphor and phosphor samples GO 1200, and GO 1350. (f) PL of the fresh, annealed, and GO-wrapped phosphors. Inset shows the variation in PL intensity with annealing and GO wrapping. (g) XRD patterns of fresh, annealed, and GO-wrapped phosphors.
Mentions: The rGO wrapping was achieved through mixing appropriate amount of GO and phosphor followed by a calcination at temperatures of 700 °C, 1200 °C, and 1350 °C for 6 h in a reducing (N2/H2) atmosphere. The annealing of GO-phosphor composite results in a wrapping of rGO around the phosphor particles. Figure 1(a) shows a schematic illustration of the synthesis of rGO wrapped phosphor. The samples of unwrapped phosphors annealed at 700, 1200 and 1350 °C are labelled as UW 700, UW 1200 and UW 1350 while those annealed with GO are labeled as GO 700, GO 1200 and GO 1350 respectively. Figure 1(b) shows digital image of the pcLED operated at 100 mA current.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.