Dual-Resonance Nanostructures for Color Downconversion of Colloidal Quantum Emitters.

We present a dual-resonance nanostructure made of a titanium dioxide (TiO2) subwavelength grating to enhance the color downconversion efficiency of CdxZn1-xSeyS1-y colloidal quantum dots (QDs) emitting at ∼530 nm when excited with a blue light at ∼460 nm. A large mode volume can be created within the QD layer by the hybridization of the grating resonances and waveguide modes, resulting in large absorption and emission enhancements. Particularly, we achieved polarized light emission with a maximum photoluminescence enhancement of ∼140 times at a specific angular direction and a total enhancement of ∼34 times within a 0.55 numerical aperture (NA) of the collecting objective. The enhancement encompasses absorption, Purcell and outcoupling enhancements. We achieved a total absorption of 35% for green QDs with a remarkably thin color conversion layer of ∼400 nm. This work provides a guideline for designing large-volume cavities for absorption/fluorescence enhancement in microLED display, detector, or photovoltaic applications.

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements.

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Previous work has exhibited enhancements in absorption, emission rates and directionality with practical limitations. In this paper, we present a Si mix antenna array to achieve a trifecta enhancement of ∼1200-fold with a Purcell factor of ∼47. The antenna design incorporates ∼10 nm gaps, within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via a Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS-compatible platforms to enhance fluorescence for biological and chemical applications.

Interplay between spontaneous decay rates and Lamb shifts in open photonic systems.

In this Letter, we describe the modified decay rate and photonic Lamb (frequency) shift of quantum emitters in terms of the resonant states of a neighboring photonic resonator. This description illustrates a fundamental distinction in the behaviors of closed (conservative) and open (dissipative) systems: the Lamb shift is bounded by the emission linewidth in closed systems while it overcomes this limit in open systems.