Electroluminescent Devices with Nanostructured ZnS:Mn Emission Layer Operated at 20 V 0-p
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Electroluminescent Devices with Nanostructured ZnS:Mn Emission Layer Operated at 20 V0-p Toshihiko Toyama, Daisuke Adachi and Hiroaki Okamoto Department of Physical Science, Graduate School of Engineering Science, Osaka University Toyonaka, Osaka 560-8531, Japan ABSTRACT We have developed a new type of a thin-film electroluminescence (TFEL) device with nanostructured (NS)-ZnS:Mn utilizing its enhanced luminescent efficiency due to the quantum confinement (QC) effects. As NS-ZnS:Mn, ZnS:Mn/Si3N4 multilayers with thicknesses of 1.9– 3.5 nm for ZnS were prepared by a rf-magnetron sputtering method. From the results of grazing incidence X-ray reflectometry and X-ray diffractmetry, formation of ZnS:Mn nanocrystals in the ZnS layers are confirmed. With a decrease in the ZnS:Mn layer thickness, the photoluminescence (PL) efficiency associated with the Mn2+ transitions is increased, and the PL excitation spectrum is shifted toward higher energies, indicating appearance of the QC effects. As the results of the application of NS-ZnS:Mn to the emission layer of the TFEL device, we have successfully observed reddish-orange emission above the threshold voltage of 12 V0-p, and the maximum luminance is 3.0 cd/m2 operated with the 1-kHz sinusoidal voltage of 20 V0-p. INTRODUCTION Luminescence properties of nanostructured (NS-) semiconductors such as nanometer-size multilayers or nanocrystals have been studied extensively in the last two decades, since they exhibit characteristics different from bulk semiconductors due to the quantum confinement (QC) effects [1]. The research interest on the QC effects on the luminescent properties has been extended from the interband transitions to the radiative transitions related to the transition metals or rare-earth elements doped in the NS-semiconductors. In particular, high photoluminescence (PL) efficiencies of Mn2+ 4T1(4G)-6A1(6S) transitions demonstrated in chemically-synthesized NS-ZnS:Mn has stimulated both basic research and application fields [2], because ZnS:Mn has been widely used as an emission layer of thin-film electroluminescence (TFEL) devices for about 30 years [3]. Many studies have been already reported about the QC effects on the PL properties of NS-ZnS doped with Mn [4], Cu [5,6], and Eu [6]. Moreover, some research groups have observed the EL from NS-ZnS:Cu [7,8], whereas, to our knowledge, there has been no report on EL from NS-ZnS:Mn. In this article, we propose a novel NS-ZnS:Mn system, i.e., a multilayer with ZnS:Mn nanocrystals sandwiched by amorphous Si3N4 [9]. The Si3N4 layer is expected to act as a role in intercepting the crystal growth of ZnS:Mn, so that the resulting ZnS:Mn layer should contain ZnS:Mn nanocrystals. First, we report structural and PL properties of NS-ZnS:Mn with a stress on the influence of the crystal size as well as the lattice constant of ZnS on the PL properties, then describe the developed low-voltage-driven TFEL device with the NS-ZnS:Mn emission layer.
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EXPERIMENTAL DETAILS The ZnS:Mn/Si3N4 multilayers were prepared on quartz subst
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