Abstract:Two metals are used in resonant layers for chemical sensors based on surface plasmon resonance (SPR) -gold and silver. Gold displays higher shift of the resonance angle to changes of ambient refraction index and is chemically stable. Silver posses narrower resonance curve thus providing a higher signal/noise ratio of SPR chemical sensors, but has a poor chemical stability. A new structure of resonant metallic film based on bimetallic silver/gold layers (gold as an outer layer) is suggested. It combines advantages of both gold and silver resonant layers. Bimetallic resonant films display so high shift of resonance angle on changes of ambient refraction index as gold films, but show narrower resonance curve, thus providing a higher signal / noise ratio. Additionally, the outer gold layer protects silver against oxidation.

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Luminescence decay of ZnS: Mn films after electric field switching-off was investigated in dependence on the Mn concentration, which changes from 0.1 to 7 wt%. The decay of electroluminescence does not depend on the charge polarization and RC-time constant of the film cell but it is determined by the kinetics of radiative transition in the Mn2+ ion. It is established that an increase of the Mn concentration above 0.3 wtyo leads to the following effects: 1) the rate of decay increases, 2) the decay curves are described a t the given concentration by a sum of two exponents rather than a simple exponential law, 3) the decay time constants of both the exponential sections decreases. On the basis of the results obtained and of literature data analysis it is concluded that the observed effects in electroluminescence decay are due not only to the concentration quenching of luminescence but to the formation of new manganese centers or the occurrence of new transitions in them, characterized by a smaller excited-state lifetime than the lifetime of Mn2+ isolated ion.Es wird das Abklingen der Lumineszenz von ZnS:Mn-Schichten nach Abschalten des elektrischen Feldes in Abhiingigkeit von der Mn-Konzentration, die zwischen 0,l und 7 Gew.yo variiert, untersucht. Der Abfall der Elektrolumineszenz hangt nicht von der Ladungspolarisation und RC-Zeitkonstante der Schichtzelle ab, sondern wird durch die Kinetik des Strahlungsiibergangs im Mn2+-Ion bestimmt. Es wird gefunden, daD eine Erhohung der Mn-Konzentration uber 0,3 Gew.% zu folgenden Effek ten fuhrt : 1) die Abklinggeschwindigkeit nimmt zu, 2) die Abklingkurven lassen sich bei der gegebenen Konzentration eher durch eine Summe von zwei Exponenten als durch ein einfaches Exponentialgesetz beschreiben, 3) die Zeitkonstante des Abklingens beider exponentieller Abschnitte nimmt ab. Auf der Grundlage dieser Ergebnisse und einer Analyse von Werten aus der Literatur wird geschlossen, daD die beobachteten Effekte des Abklingens der Elektrolumineszenz nicht durch eine Konzentrationstilgung der Lumincszenz, sondern durch das Auftreten neuer Manganzentren oder durch das Auftreten von neuen ubergiingen in ihnen hervorgerufen werden, die durch eine kiirzere Lebensdauer der angeregten Zustiinde als die Lebensdauer der isolierten Mn2+-Ionen charakterisiert aind.

A polarization which remains constant over a period of time and is caused by the accumulation of carriers in deep surface traps is observed in EL ZnS-Mn films. The polarization characteristics (i.e., the number of polarization charges, the time-dependence of its formation and destruction, the ionization energy of the traps, etc.) are determined in order to study the role of carrier polarization in the mechanism of EL. It is established that the polarization mainly affects t.he change in the internal field and therefore the impact ionization probability. Also, at the instant of voltage-polarity reversal, the polarization charge ionization leads to an increase in the number of carriers which can accelerate. All the EL properties and features of ZnS-Mn films may be explained on the basis of an impactionization mechanism if the polarization effects are taken into account.