Yasuhiro Shirasaki

High‐Performance Shortwave‐Infrared Light‐Emitting Devices Using Core–Shell (PbS–CdS) Colloidal Quantum Dots

Core-shell PbS-CdS quantum dots enhance the peak external quantum efficiency of shortwave-infrared light-emitting devices by up to 50-100-fold (compared with core-only PbS devices). This is more than double the efficiency of previous quantum-dot light-emitting devices operating at wavelengths beyond 1 μm, and results from the passivation of the PbS cores by the CdS shells against in situ photoluminescence quenching.

Electroluminescence from Nanoscale Materials via Field-Driven Ionization

The high degree of morphological and energetic disorder inherent to many nanosized materials places limitations on charge injection into and transport rates through thin films of these materials. We demonstrate electroluminescence achieved by local generation of charge that eliminates the need for injection of charge carriers from the device electrodes. We show electroluminescence from thin films of nanoscale materials that do not support direct current excitation and suggest a mechanism for the charge generation and electroluminescence that is consistent with our time-averaged and time-resolved observations.

Study of field driven electroluminescence in colloidal quantum dot solids

Semiconductor nanocrystals, or quantum dots (QDs), promise to drive advances in electronic light generation. It was recently shown that long range transport of charge, which is typically required for electric excitation and which is inherently limited in nanosized materials, can be avoided by developing devices that operate through local, field-assisted generation of charge. We investigate such devices that consist of a thin film of CdSe/ZnS core-shell QD placed between two dielectric layers and that exhibit electroluminescence under pulsed, high field excitation. Using electrical and spectroscopic measurements, we are able to elucidate the dynamics of charge within the QD layer and determine that charge trapping and field-induced luminescence quenching are the main limitations of device performance.

Resonant cavity colloidal quantum dot LEDs

We demonstrate resonant-cavity colloidal quantum dot light-emitting diodes that exhibit electroluminescence with enhanced spectral purity and directionality and show that the enhancement is due to modification of the optical modes of the system.

Exciton-polaritons at room temperature in dielectric microcavities exhibiting rabi-splitting Ω R ≫ 100 meV

Exciton-Polariton states are observed at room temperature in planar sputter-coated dielectric microcavities containing 5 nm thick film of J-aggregated dye as excitonic layer exhibiting Rabi-splitting Ω_R ≫ 100meV and empty cavity Q factor ≫> 700.