PVK Emission Research Articles

Photoluminescent and electroluminescent properties of Mn-doped ZnS nanocrystals

ZnS:Mn nanocrystals with sizes between 3 and 4 nm were synthesized via a competitive reaction chemistry method, where the surface capping organic species (p-thiocresol) is used as an inhibitor of the crystal growth. The x-ray diffraction and photoluminescent (PL) properties of ZnS:Mn bulk and nanocrystals were compared. A direct current electroluminescent (EL) device having a hybrid organic/inorganic multilayer structure, indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS)/PVK/ZnS:Mn NC/Al, was tested. In this multilayer EL device structure, the PEDOT-PSS leads to enhanced hole injection, while the poly(N-vinylcarbazole) (PVK) serves as a passivation layer between the PEDOT-PSS and nanocrystal layers. Electron–hole recombination was not confined to the ZnS:Mn nanocrystal layer, but also occurred in the PVK layer. The result was emission from both the blue-emitting PVK and yellow-emitting ZnS:Mn nanocrystals. The EL emission spectrum was dependent upon the voltage, showing an increasing ratio of PVK emission to nanocrystal emission with increased voltage. The dependence of PL and EL emissions on Mn concentration (0.40 to 2.14 mol %) is also reported.

Long-Range Energy Migration in Photoexcited Polymers

Excitation migration dynamics and the energy-transfer process in a donor−acceptor pair system on photoexcitation have been investigated by using static and time-resolved photoluminescence (PL) measurements. The PL spectrum of poly(N-vinylcarbazole) (PVK) was fully superposed on the electronic absorption spectrum of poly(9,9‘-di-n-hexyl-2,7-fluorenylvinylene) (PDHFV) to fulfill a requirement for an efficient Förster-type energy transfer. In the PL spectrum of a blended PVK film with 0.5 wt % PDHFV on photoexcitation at 340 nm, the PL emission of PDHFV, which exhibits little absorbance at the excitation wavelength, prevailed over the PL emission of PVK. The PL spectrum of a bilayered structure with a PVK layer thickness of 4 μm and a PDHFV layer thickness of 80 nm, which was prepared by spin-casting PDHFV solution in trichloroethylene on a PVK film, also showed the PL emission of PDHFV on photoexcitation of the PVK layer at 340 nm without a trace of the PL emission of PVK. Excitation energy migration through a PVK bulk was observed up to a PVK thickness of 23 μm. A time-correlated single-photon counting (TCSPC) study deduced an energy migration velocity of 3.5 × 106 cm/s and a dwell time between each hopping of 85 fs, respectively, in the PVK bulk of the bilayered structures with a PDHFV layer thickness of 10 or 80 nm.