Off-Angle Amplified Spontaneous Emission of Upconversion Nanoparticles by Propagating Lattice Plasmons

Lanthanide-doped upconversion nanoparticles (UCNPs) are appealing for light emitting applications because their high internal conversion efficiency facilitates the amplified spontaneous emission (ASE) under low pumping. In addition, the integration of photonic crystals and microcavities with optical quantum emitters provides a unique opportunity to manipulate their light emissions and generate coherent light sources for quantum photonics. Here, this work describes a two-dimensional (2D) plasmonic lattice of Al nanocone array (Al NCA), which can confine the light at the tip. Light confinement by the enhancement effect supports narrow linewidth resonances as optical feedback for the ASE of UCNPs doped with sensitizer Yb³⁺ ions/emitter Ho³⁺ ions/relaxator Ce³⁺ ions. An off-angle ASE with an enhancement of 19-fold from UCNPs is achieved by propagating lattice plasmons from the Al NCA. Moreover, this upconverting ASE can be switched on or off by adjusting the polarization state of the incident pump light, and photonic band engineering can be used to manipulate it intentionally. This composite plasmonic system opens prospective applications for the ASE as directional emission, real-time tunable wavelengths, controlled multimode lasing, and optical switches.