Photoluminescence (PL) is a fundamental optical process that defines how some materials emit light after absorbing electromagnetic radiation. It occurs routinely in the natural world, but experts in the field of photonics have endeavored to recreate and exploit this process artificially for decades. The genesis of two-dimensional (2D) structures like monolayer graphene has opened new avenues of opportunity for developing brightly photoluminescent materials.
Monolayer Graphene: Finding a Niche in Photonics
Since the late 1980s, research and development (R&D) in this area of photonics has largely focused on the actualization of quantum dots (QDs). These nanoscale semiconductor crystals emit light of highly predictable wavelengths when stimulated by either electricity or photons. These emission wavelengths are strongly size- and chemistry-dependent. By fine-tuning the composition and geometries of QDs, it is possible to reproduce virtually any color present in nature. However, there are limitations that hinder this revolutionary technology from truly disrupting modern electronics markets.
Several approaches to QD technology currently exist, few of which alleviate concerns about the inherent toxicity of the strongest available compounds (cadmium selenide, indium phosphide, etc.). In the absence of a single solution to developing bright photoluminescent materials for new applications, researchers have explored potential contenders to QDs. Monolayer graphene has emerged as one such contender.
What is Photoluminescence?
Before outlining the photoluminescent qualities of monolayer graphene, it is worth exploring the concept of photoluminescence in more depth. Since the process relies on absorption, candidate materials must be strong absorbers to particular wavelengths of light – typically on the ultraviolet-visible range (~100 – 700nm). This absorption causes low-level electrons to transition to higher energy bands in the materials’ electronic structure. As the electron relaxes back to its original position, the atom releases energy in the form of electromagnetic radiation; the wavelength and frequency of which is determined by the bandgap.
Photoluminescent Properties of Monolayer Graphene
The photoluminescent qualities of monolayer graphene have been explored as part of wider research efforts to fully characterize the material. Since graphene was first isolated in 2004, extensive testing has yielded many positive results regarding its optoelectronic and mechanical properties, fuelling a global interest that often verges on hyperbolic.
The response to monolayer graphene from the photonics community was comparatively muted, however. This is because the material is a semi-metal with zero bandgap; a consequence of its single-atom thickness. Monolayer graphene is subsequently not a photoluminescent material. However, recent research has shown that monolayer graphene could still prove instrumental in the search for ideal photoluminescent materials.
In a process like doping of semiconductors, researchers have shown that photoluminescence can be induced in monolayer graphene flakes and carbon nanotubes by deliberately introducing ‘defects’ into their structural lattices. Several processes have successfully introduced bandgaps into monolayer graphene, but further research is required to establish the emission properties of materials derived from these methods.
Further research has explored the importance of gating in the electrophysiology of monolayer graphene, demonstrating the material’s insensitivity to continuous wavelength (CW) lasers. Using femtosecond lasers, which emit infrared (IR) radiation pulses on an order of 10-15 seconds. Studies observed ultrafast photoluminescence in ion-gel gated monolayer graphene that could be controlled via electrical gating. The ramifications of this are extraordinary, particularly for specialists working with monolayer graphene in emerging electrical applications.
Monolayer Graphene from Grolltex
Grolltex specializes in the generation and transfer of monolayer graphene via patented techniques. We generate high purity 2D materials and transfer such to substrates of your choosing. If you would like to learn more about our production capabilities, simply contact a member of the team today.