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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–f) TEM and HRTEM images of GO 1200, (g–l) TEM and HRTEM images of GO 1350. The wrapping of rGO over GO 1200 phopshors is clearly visibile, while in GO 1350, the self-wrapping of rGO sheets results in the formation of nanoscrolls.
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f2: (a–f) TEM and HRTEM images of GO 1200, (g–l) TEM and HRTEM images of GO 1350. The wrapping of rGO over GO 1200 phopshors is clearly visibile, while in GO 1350, the self-wrapping of rGO sheets results in the formation of nanoscrolls.

Mentions: For samples GO 1200 and GO 1350, we investigated the crystalline nature of the rGO and further characterized its wrapping of the phosphor particles using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Figure 2(a–f) are HRTEM images from sample GO 1200 and Fig. 2(g–l) are images from sample GO 1350. Figure 2(a,b) are images of phosphor particles that are wrapped in rGO. Figure 2(c–e) confirm that the phosphor particles are wrapped with several layers of rGO sheets. Figure 2(f) is an HRTEM image of rGO sheets, which exhibits lattice fringes indicative of the honeycomb lattice. The selected area electron diffraction (SAED) pattern from this section is shown in the inset of Fig. 2(f), and it confirms the hexagonal symmetry and highly ordered nature of the rGO. Only six spots are observed in the inner hexagon of the SAED pattern, which can be indexed as a single crystal of AB Bernal stacked graphite20. The d value calculated from the spacing of HRTEM images is 0.37 nm, which is slightly high compared to the standard value of 0.34 nm for (0002) plane spacing. This is presumably because of the presence of a small percentage of oxygen functional groups.


Reduced graphene oxide enwrapped phosphors for long-term thermally stable phosphor converted white light emitting diodes
(a–f) TEM and HRTEM images of GO 1200, (g–l) TEM and HRTEM images of GO 1350. The wrapping of rGO over GO 1200 phopshors is clearly visibile, while in GO 1350, the self-wrapping of rGO sheets results in the formation of nanoscrolls.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: (a–f) TEM and HRTEM images of GO 1200, (g–l) TEM and HRTEM images of GO 1350. The wrapping of rGO over GO 1200 phopshors is clearly visibile, while in GO 1350, the self-wrapping of rGO sheets results in the formation of nanoscrolls.
Mentions: For samples GO 1200 and GO 1350, we investigated the crystalline nature of the rGO and further characterized its wrapping of the phosphor particles using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Figure 2(a–f) are HRTEM images from sample GO 1200 and Fig. 2(g–l) are images from sample GO 1350. Figure 2(a,b) are images of phosphor particles that are wrapped in rGO. Figure 2(c–e) confirm that the phosphor particles are wrapped with several layers of rGO sheets. Figure 2(f) is an HRTEM image of rGO sheets, which exhibits lattice fringes indicative of the honeycomb lattice. The selected area electron diffraction (SAED) pattern from this section is shown in the inset of Fig. 2(f), and it confirms the hexagonal symmetry and highly ordered nature of the rGO. Only six spots are observed in the inner hexagon of the SAED pattern, which can be indexed as a single crystal of AB Bernal stacked graphite20. The d value calculated from the spacing of HRTEM images is 0.37 nm, which is slightly high compared to the standard value of 0.34 nm for (0002) plane spacing. This is presumably because of the presence of a small percentage of oxygen functional groups.

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.