Reni Tomova
Bulgarian Academy of Sciences, IOMT, Post-Doc
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Ion-selective membranes on the basis of thin evaporated layers of pure and doped chalcogenide glasses have been developed. The membranes showed high sensitivity towards Ag+ and Cu2+ ions -down to 10 -6 mol/L, short response time and good... more
Ion-selective membranes on the basis of thin evaporated layers of pure and doped chalcogenide glasses have been developed. The membranes showed high sensitivity towards Ag+ and Cu2+ ions -down to 10 -6 mol/L, short response time and good selectivity to interfering ions. The electrochemical sensors for Pb2+ ions however are not at the same level. The reasons for this difference have been established by examining the physical properties, AES depth-profile and electrochemical behavior of the three types of membranes. In spite of the promising results and good electrochemical performance, the long-term stability of chalcogenide-based thin film sensors is still a problem. It was established that the plasma deposited polymer film of (PHMDSO) and vacuum deposited polyimide (PI) on the top of chalcogenide glass membrane improve the electrochemical characteristics - increases the sensitivity and long-term stability and keeps the response time. The results obtained are promising for the devel...
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In this article we demonstrate White Organic Light Emitting Diodes (WOLEDs) using yellow-emitting iridium complex bis(2-phenylbenzothiazolato) (acetyl-acetonate)iridium(III) (Ir(bt) 2 acac), as a dopant in the hole-transporting layer... more
In this article we demonstrate White Organic Light Emitting Diodes (WOLEDs) using yellow-emitting iridium complex bis(2-phenylbenzothiazolato) (acetyl-acetonate)iridium(III) (Ir(bt) 2 acac), as a dopant in the hole-transporting layer (composed of N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) dispersed in poly(N-vinylcarbazole) (PVK) matrix. Bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq) and bis(2-(2-hydroxyphenyl) benzothiazolate)zinc (Zn(btz) 2) were used as electroluminescent and electron-transporting materials. It was found that OLED with 2.5 wt % Ir(bt) 2 acac irradiated a white light which CIE coordinates changed from bluish-white (0.28, 0.30) at 8 V, to yellowish-white (0.35, 0.40) at 20 V.
In this work the results from a comparative study of electroluminescent and photophysical properties of four Zn chelate complexes based on benzothiazoles and quinolines ligands (zinc bis-[8-hydroxyquinoline], zinc [8-hydroxyquinoline]... more
In this work the results from a comparative study of electroluminescent and photophysical properties of four Zn chelate complexes based on benzothiazoles and quinolines ligands (zinc bis-[8-hydroxyquinoline], zinc [8-hydroxyquinoline] acetylacetonate, zinc bis[2-(2-hydroxyphenyl) benzothiazole], zinc 2-(2-hydroxyphenyl) benzothiazole acetylacetonate), and their application in Organic Lght-emitting Diodes (OLED) are presented. The absorption, photoluminescence spectra and morphology of thin films of Zn complexes were investigated. The luminance-voltage (L-V) characteristics, efficiencies and electroluminescences of the diodes based on bilayer structure ITO/HTL/Zn complex/Al were determined.
We report studies on the color tunability of a novel type of multilayer organic light-emitting diodes (OLEDs) based on three emitting materials: DCM (4-(Dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran) as a red emitter,... more
We report studies on the color tunability of a novel type of multilayer organic light-emitting diodes (OLEDs) based on three emitting materials: DCM (4-(Dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran) as a red emitter, DPVBi [4,4'-Bis(2,2-diphenylvinyl)-1,1'-biphenyl] as a blue emitter and zinc bis(2-(2-hydroxyphenyl) benzothiazole) (Zn(BTz)2) as a yellow emitter, and an electron transporting layer. We established that the positions and thicknesses of the different emitting layers determine the efficiencies, luminance and color of the light emitted by the OLEDs.
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ABSTRACT Thin film sensors on the basis of evaporated layers of chalcogenide glasses for heavy metal ions are developed. In spite of the promising results and good electrochemical performance, the long-term stability of chalcogenide-based... more
ABSTRACT Thin film sensors on the basis of evaporated layers of chalcogenide glasses for heavy metal ions are developed. In spite of the promising results and good electrochemical performance, the long-term stability of chalcogenide-based thin film sensors is still a problem. In this paper, AES study was made to clarify the problem with “the aging” of chalcogenide thin film membranes.The electrochemical performance of chalcogenide glass membranes covered with plasma deposited polymer film of polyhexamethyldisiloxane (PHMDSO) and vacuum deposited polyimide (PI) was investigated. It was established that both polymer layers improve the electrochemical characteristics of the membranes—increase the sensitivity, the detection limits and long-term stability while maintaining a stable response time and very good reproducibility.
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Organic light-emitting diodes (OLEDs) with improved performances are fabricated using a thin (1 nm) yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (Rubrene) inserted at different position in green emitting electroluminescent... more
Organic light-emitting diodes (OLEDs) with improved performances are fabricated using a thin (1 nm) yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (Rubrene) inserted at different position in green emitting electroluminescent (EL) layer of bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTz)2) in configuration: ITO/PVK:TPD/ Zn(BTz)2 (x nm)/ Rubrene (1 nm)/ Zn(BTz)2 (75-x nm)/Al, where PVK:TPD is a hole transporting layer of N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD) incorporated in poly(N-vinylcarbazole) (PVK) matrix and Al is a cathode. EL spectra predominantly influenced by Rubrene emission when the doping layer is close to (PVK:TPD)/ Zn(BTz)2 (x→ 0-15 nm) and to Zn(BTz)2/Al (x→ 70-75 nm) interfaces and shift toward emission of Zn(BTz)2 increasing the distance of Rubrene from both interfaces (x→35 nm). The same dependence of the EL efficiency on the position of the doping Rubrene layer in the OLED structure was found.
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In this paper we present our results concerning the role of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, BCP) in OLED structures with emissive layer of Tris-(8-hydroxyquinoline) aluminum (Alq3). It is established that... more
In this paper we present our results concerning the role of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, BCP) in OLED structures with emissive layer of Tris-(8-hydroxyquinoline) aluminum (Alq3). It is established that instead of the higher working voltage of devices with bathocuproine their current efficiency significantly increased. This higher efficiency indicates strong hole-blocking nature of bathocuproine (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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The characteristics of organic light-emitting devices based on aluminum tris-(8-hydroxy-quinoline) (Alq3), N,N'<!--inline-formula... more
The characteristics of organic light-emitting devices based on aluminum tris-(8-hydroxy-quinoline) (Alq3), N,N'<!--inline-formula content-type="tex">N^'</inline-formula-->-bis(3-methylphenyl)-N,N'<!--inline-formula content-type="tex">N^'</inline-formula-->-diphenylbenzidine (TPD) with novel p-isopropenyl-calix[8]arenestyrene copolymer buffer layer and Al cathode were investigated. The devices with TPD/Alq3/Al were also fabricated in the same way for comparison. The p-isopropenylcalix[8]arenestyrene copolymer used as buffer layer greatly improved the performance of the device and increased the device efficiency and stability.