Giant Enhancement of Defect-Bound Exciton Luminescence and Suppression of Band-Edge Luminescence in Monolayer WSe₂–Ag Plasmonic Hybrid Structures

We have investigated how the photoluminescence (PL) of WSe₂ is modified when coupled to Ag plasmonic structures at low temperature. Chemical vapor deposition (CVD) grown monolayer WSe₂ flakes were transferred onto a Ag film and a Ag nanotriangle array that had a 1.5 nm Al₂O₃ capping layer. Using low-temperature (7.5 K) micro-PL mapping, we simultaneously observed enhancement of the defect-bound exciton emission and quenching of the band edge exciton emission when the WSe₂ was on a plasmonic structure. The enhancement of the defect-bound exciton emission was significant with enhancement factors of up to ∼200 for WSe₂ on the nanotriangle array when compared to WSe₂ on a 1.5 nm Al₂O₃ capped Si substrate with a 300 nm SiO₂ layer. The giant enhancement of the luminescence from the defect-bound excitons is understood in terms of the Purcell effect and increased light absorption. In contrast, the surprising result of luminescence quenching of the bright exciton state on the same plasmonic nanostructure is due to a rather unique electronic structure of WSe₂: the existence of a dark state below the bright exciton state

Mn²⁺-Doped CdSe/CdS Core/Multishell Colloidal Quantum Wells Enabling Tunable Carrier–Dopant Exchange Interactions

In this work, we report the manifestations of carrier–dopant exchange interactions in colloidal Mn²⁺-doped CdSe/CdS core/multishell quantum wells. The carrier–magnetic ion exchange interaction effects are tunable through wave function engineering. In our quantum well heterostructures, manganese was incorporated by growing a Cd_0.985Mn_0.015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. Unlike previously synthesized Mn²⁺-doped colloidal nanostructures, the location of the Mn ions was controlled with atomic layer precision in our heterostructures. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions by adjusting the location, composition, and number of the CdSe, Cd_1–<i>x</i>Mn_<i>x</i>S, and CdS layers. The photoluminescence quantum yield of our magnetic heterostructures was found to be as high as 20% at room temperature with a narrow photoluminescence bandwidth of ∼22 nm. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices