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

Gopinathan Anoop,Shinill Kang,Janardhanan R Rani,Juhwan Lim,Dong Wook Suh,Jae Soo Yoo,Seong Chan Jun,Myoung Soo Jang

doi:10.1038/srep33993

Gopinathan Anoop, Shinill Kang + Show 6 more

Open Access

https://doi.org/10.1038/srep33993

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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.

Highlights

The long-term instability of the presently available best commercial phosphor-converted light-emitting diodes is the most serious obstacle for the realization of low-cost and energy-saving lighting applications
An field emission scanning electron microscope (FESEM) image of a GO 1200 phosphor particle is shown in Fig. 1(d), and it is apparent that there is a change in contrast of the particle surface, apparently due to the reduced graphene oxide (rGO) wrapping
The thermal degradation in phosphor-converted LEDs (pcLEDs) has been effectively controlled through wrapping of rGO around phosphor particles using a simple solid-state reaction

Summary

Introduction

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. 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. In solid state lighting technology, the most widely accepted method for white light generation is to use a blue GaN-based or InGaN-based light-emitting diode (LED) with a conversion phosphor (embedded in epoxy resin/ binder) that partially converts blue light into yellow light. This would offer a wider choice among the available phosphors that show excellent conversion efficacy and would extend the lifetime of pcLEDs. One possible way of thermal management in pcLEDs is wrapping the conversion phosphors using materials having high thermal conductivity and high optical transparency. We find that rGO wrapping serves as an excellent thermal management material, and pcLEDs fabricated in this manner exhibit long-term reliability, unlike pcLEDs fabricated with unwrapped phosphor

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