Enhancing two-photon spontaneous emission in rare earths using graphene and graphene nanoribbons

The enhancement of two-photon spontaneous emission (2PSE) from trivalent and divalent rare earth ions in proximity to graphene and graphene nanoribbons is calculated for achievable experimental conditions using a combination of finite difference time domain simulations and direct computation of transition rates between energy levels in rare earths. For Er3+, we find that the 2PSE rate is initially 8 orders lower than the single-photon spontaneous emission rate but that, with enhancement, 2PSE can reach 2.5% of the overall decay. When graphene nanoribbons are used, we also show that the emission of free-space photon pairs from Er3+ at 3-3.2 mu m via 2PSE can be increased by -400. Our calculations show significantly less relative graphene-enhanced 2PSE than previous works, and we attribute this variation to differences in emitter size and assumed graphene mobility. We also show that the internal energy structure of the ion can have an impact on the degree of 2PSE enhancement achievable and find that divalent rare earths are more favorable.

Automated summary

This study calculates the enhancement of two-photon spontaneous emission (2PSE) from trivalent and divalent rare earth ions in proximity to graphene and graphene nanoribbons using finite difference time domain simulations and direct computation of transition rates. The results show that with enhancement, 2PSE can reach 2.5% of the overall decay for Er3+. The use of graphene nanoribbons can also significantly increase the emission of free-space photon pairs from Er3+ at 3-3.2 μm via 2PSE. The study also highlights the impact of emitter size, assumed graphene mobility, and the internal energy structure of the ion on the degree of 2PSE enhancement achievable.