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

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.

An Ultra-High-Energy Density Supercapacitor; Fabrication Based on Thiol-functionalized Graphene Oxide Scrolls

“…The driving force for the scrolling of the thiolated GO is the energy difference between the total surface energy of the system and the elastic energy associated with thiolated GO bending [ 20 , 21 ]. When the temperature increases during annealing, the GO layer bends to minimize the total surface energy of the system by reducing the exposed surfaces of the thiolated GO layers, and the subsequent rolling of the graphene oxide is driven by the reduction of the total area of the exposed GO surface.…”

Improvement in luminescent properties and thermo-optical conversion mechanism of Na2SiF6:Mn4+,K+@GQDs

“…29 Furthermore, it is encouraging is that aer the SrBaSi 2 O 2 N 2 :Eu 2+ phosphor was coated by rGO, the long-range thermal stability of the coated sample was enhanced compared with that of the uncoated control sample. 30 In conclusion, given that the coating of GQDs or rGO can enhance the luminescent intensity or thermal stability of rare earth compounds or rare earth-doped phosphors, then similarly, the coating of GQDs or rGO may also enhance the luminescent intensity or luminescent thermal stability of Mn 4+doped uoride phosphors.…”

“…Due to their high surface area, conjugated large p bonds, wide applications, environment friendliness, and high thermal stability, carbon-based monolayer nanosheets, such as graphene, graphite oxide (GO), reduced graphene oxide (rGO) and GQDs are considered advanced functional carbon nanomaterials. [28][29][30] Thus, many research efforts have been focused on using carbon nanomaterials. It is interesting that the luminescence of some rare earth compounds can be signicantly enhanced by carbon nanosheets.…”

Cellulose Nanocrystal Templated Graphene Nanoscrolls for High Performance Supercapacitors and Hydrogen Storage: An Experimental and Molecular Simulation Study

“…GNS are morphologically similar to multiwalled carbon nanotubes(CNTs); however, their open end structures, variable scrolling density and tunable inter-layer spacing provides a unique opportunity to inherit favorable properties of both CNTs and graphene 1 , 2 . The tubular nanochannels and high porosity present in GNS provides pathway for intercalation of ionic species in its inter-galleries resulting in higher electrical conductivities compared to graphene with practical applications in electrochemical charge storage devices 3 and electronics 4 . In literature, molecular simulation-based studies on the formation of GNS and theoretical predictions of its properties, have been extensively studied 5 , 6 .…”