2 research outputs found
Charging and Charged Species in Quantum Dot Light-Emitting Diodes
Despite
recent rapid advances in improving quantum dot light-emitting
diodes, many fundamental aspects of the device operating mechanism
remain unresolved. Through transient electroluminescence and time-resolved
photoluminescence measurements, the effects of offset voltage on charging
and charge transport are examined. First, capacitive charging occurs
with a time constant of ∼500 ns, followed by electron transport
through quantum dots with a mobility of ∼10–5 cm2 V–1 s–1. Hole
injection then initiates an electroluminescence rise that is independent
of offset voltage. The photoluminescence lifetime is also unaffected
by the offset voltage, indicating no injection of charges into the
quantum dots or on their surfaces prior to the voltage pulse. A slower
equilibration to steady-state electroluminescence is dependent on
the offset voltage, indicative of another charging process. Elemental
mapping shows that ZnO deposition from solution can lead to the diffusion
of charged species into the quantum dot layer, which may cause the
slower process
Capturing Phase Evolution during Solvothermal Synthesis of Metastable Cu<sub>4</sub>O<sub>3</sub>
The metastability of Cu<sub>4</sub>O<sub>3</sub> has long hindered
the synthetic preparation of bulk samples with substantial crystallinity.
The lack of suitable samples has thwarted the detailed understanding
of the magnetic properties of Cu<sub>4</sub>O<sub>3</sub> and the
ability to tune its properties. While Cu<sub>4</sub>O<sub>3</sub> was
recently shown to form in solvothermal reactions, the results are
unpredictable, and the crystals are small. We developed a new, more
uniform synthesis technique using sealed fused silica tubes. Interrogation
of the solid and liquid phases resulting from this reaction has shed
more light on the kinetic evolution of copper-containing phases and
the microstructural correlation between different precipitation products.
We find that direct conversion of the intermediate phase Cu<sub>2</sub>(NO<sub>3</sub>)Â(OH)<sub>3</sub> to Cu<sub>4</sub>O<sub>3</sub> is
a likely consequence of dimethylformamide (DMF) triggered <i>in situ</i> reduction. The optimal reduction environment should
be more straightforward to attain given the improved reliability of
our method, and it remains under investigation. We verify the formation
of Cu<sub>4</sub>O<sub>3</sub> via X-ray diffraction, Raman microscopy,
and SQUID magnetometry