Electroluminescence from Phosphor-doped nanocrystals
Alternating current thin-film electroluminescent (ACTFEL) devices already occupy a segment of the largearea, high-resolution, flat-panel-display market. The AC-TFEL displays, which consist of a phosphor layer, such as manganese doped-zinc sulfide (ZnS:Mn), vertically sandwiched between two insulators that are contacted by electrodes, are robust, possess long lifetimes, and offer high luminance with relatively low power consumption [1], [2]. While fabrication of AC-TFEL devices has been the subject of considerable study over the past three decades, significant challenges remain. Development of multicolor displays with balanced red, green, and blue (RGB) emission has proven difficult as the most efficient red, green, and blue phosphors comprise different materials systems that require different deposition and annealing steps. Transparent AC-TFEL displays have recently been demonstrated by Sharp, Inc.; however, the processing of the phosphor to achieve transparency is difficult and has not yet been developed for phosphors other than ZnS:Mn [3].
Efficient emission from core/(doped) shell nanoparticles: applications for chemical sensing.
We have studied manganese doping of zinc selenide core/zinc sulfide shell nanocrystals (NCs) where the impurity phosphor resides primarily in the shell. We have found that a simple two-step synthesis can be used to create these nontoxic materials that display efficient energy transfer from the core to the Mn doped shell. These core/shell NCs retain ample quantum efficiency ( approximately 25%) when solubilized in water, which opens the possibility of using these materials as bioimaging agents. As recent work has shown that nanocrystals can be functionalized with organic dyes to operate as ratiometric chemical sensing agents, we have conjugated the doped NCs with an organic dye to showcase efficient Förster resonant energy transfer from the shell-doped phosphor to the surface-bound dye. This result indicates that doped NCs can be used to develop nontoxic ratiometric sensing/biological imaging agents.
Aging studies of atomic layer epitaxy ZnS:Mn alternating‐current thin‐film electroluminescent devices
A study of the aging behavior of atomic layer epitaxy (ALE) ZnS:Mn alternating‐current thin‐film electroluminescent (ACTFEL) devices is undertaken by monitoring the internal charge‐phosphor field (Q‐Fp) and capacitance‐voltage (C‐V) characteristics as a function of aging time. The electrical properties of ALE ZnS:Mn ACTFEL devices are asymmetrical with respect to the applied voltage pulse polarity; the aging characteristics of such devices are also asymmetric. The electrical asymmetries are attributed to differences in the interface state densities at the top and bottom phosphor/insulator interfaces. The presence of Cl at the indium tin oxide interface and its tendency to migrate into the ZnS during aging is believed to be the major cause of the observed asymmetrical aging characteristics.