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Dive into the research topics where Gediminas Kreiza is active.

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Featured researches published by Gediminas Kreiza.


Applied Physics Letters | 2015

Fluorene- and benzofluorene-cored oligomers as low threshold and high gain amplifying media

Karolis Kazlauskas; Gediminas Kreiza; Olegas Bobrovas; Ona Adomėnienė; Povilas Adomėnas; Vygintas Jankauskas; S. Juršėnas

Deliberate control of intermolecular interactions in fluorene- and benzofluorene-cored oligomers was attempted via introduction of different-length alkyl moieties to attain high emission amplification and low amplified spontaneous emission (ASE) threshold at high oligomer concentrations. Containing fluorenyl peripheral groups decorated with different-length alkyl moieties, the oligomers were found to express weak concentration quenching of emission, yet excellent carrier drift mobilities (close to 10−2 cm2/V/s) in the amorphous films. Owing to the larger radiative decay rates (>1.0 × 109 s−1) and smaller concentration quenching, fluorene-cored oligomers exhibited down to one order of magnitude lower ASE thresholds at higher concentrations as compared to those of benzofluorene counterparts. The lowest threshold (300 W/cm2) obtained for the fluorene-cored oligomers at the concentration of 50 wt % in polymer matrix is among the lowest reported for solution-processed amorphous films in ambient conditions, wha...


Applied Physics Letters | 2018

Exciton diffusion in bifluorene single crystals studied by light induced transient grating technique

Paulius Baronas; Patrik Ščajev; Vladislavas Čerkasovas; Gediminas Kreiza; Povilas Adomėnas; Ona Adomėnienė; Karolis Kazlauskas; Chihaya Adachi; S. Juršėnas

Exciton diffusion is considered to be of prime importance for controlling the recombination zone in organic light emitting devices. This is particularly relevant for organic lasers based on single crystals, where undesirable exciton-exciton annihilation at high concentrations is inevitable. Here, exciton diffusion is studied in bifluorene single crystals specifically designed for organic laser applications, therefore featuring exceptionally low threshold of light amplification. The non-destructive light induced transient grating (LITG) technique capable of simultaneously evaluating the exciton lifetime and diffusion coefficient along different directions of the crystal was employed for this study. Highly anisotropic singlet exciton diffusion with the diffusion coefficient varying from <0.05 up to 0.96 cm2/s (in a perpendicular direction) and the corresponding diffusion lengths changing from <60 up to 300 nm, respectively, was revealed in ethylene-bridged bifluorene crystals. The LITG results on the directionality of exciton diffusion are anticipated to be essential for devising single crystal based organic lasers.Exciton diffusion is considered to be of prime importance for controlling the recombination zone in organic light emitting devices. This is particularly relevant for organic lasers based on single crystals, where undesirable exciton-exciton annihilation at high concentrations is inevitable. Here, exciton diffusion is studied in bifluorene single crystals specifically designed for organic laser applications, therefore featuring exceptionally low threshold of light amplification. The non-destructive light induced transient grating (LITG) technique capable of simultaneously evaluating the exciton lifetime and diffusion coefficient along different directions of the crystal was employed for this study. Highly anisotropic singlet exciton diffusion with the diffusion coefficient varying from <0.05 up to 0.96 cm2/s (in a perpendicular direction) and the corresponding diffusion lengths changing from <60 up to 300 nm, respectively, was revealed in ethylene-bridged bifluorene crystals. The LITG results on the direct...


ACS Applied Materials & Interfaces | 2018

Low-Threshold Light Amplification in Bifluorene Single Crystals: Role of the Trap States

Paulius Baronas; Gediminas Kreiza; Povilas Adomėnas; Ona Adomėnienė; Karolis Kazlauskas; Jean Charles Ribierre; Chihaya Adachi; S. Juršėnas

Organic single crystals (SCs) expressing long-range periodicity and dense molecular packing are an attractive amplifying medium for the realization of electrically driven organic lasers. However, the amplified spontaneous emission (ASE) threshold (1-10 kW/cm2) of SCs is still significantly higher compared to those of amorphous neat or doped films. The current study addresses this issue by investigating ASE properties of rigid bridging group-containing bifluorene SCs. Introduction of the rigid bridges in bifluorenes enables considerable reduction of nonradiative decay, which, along with enhanced fluorescence quantum yield (72-82%) and short excited state lifetime (1.5-2.5 ns), results in high radiative decay rates (∼0.5 × 109 s-1) of the SCs, making them highly attractive for lasing applications. The revealed ASE threshold of 400 W/cm2 in acetylene-bridged bifluorene SCs is found to be among the lowest ever reported for organic crystals. Ultrafast transient absorption spectroscopy enabled one to disclose pronounced differences in the excited state dynamics of the studied SCs, pointing out the essential role of radiative traps in achieving a record low ASE threshold. Although the origin of the trap states was not completely unveiled, the obtained results clearly evidence that the crystal doping approach can be successful in achieving extremely low ASE thresholds required for electrically pumped organic laser.


Dyes and Pigments | 2015

Sol-gel synthesis, characterization and application of selected sub-microsized lanthanide (Ce, Pr, Nd, Tb) ferrites

Olga Opuchovic; Gediminas Kreiza; Jurate Senvaitiene; Karolis Kazlauskas; Aldona Beganskiene; Aivaras Kareiva


Journal of Physical Chemistry C | 2014

Morphology and Emission Tuning in Fluorescent Nanoparticles Based on Phenylenediacetonitrile

Karolis Kazlauskas; Gediminas Kreiza; Eglė Arbačiauskienė; Aurimas Bieliauskas; Vytautas Getautis; Algirdas Šačkus; S. Juršėnas


Physical Chemistry Chemical Physics | 2015

Concentration effects on spontaneous and amplified emission in benzo[c]fluorenes

Karolis Kazlauskas; Gediminas Kreiza; Edvinas Radiunas; Povilas Adomėnas; Ona Adomėnienė; Karolis Karpavičius; Jonas Bucevicius; Vygintas Jankauskas; S. Juršėnas


Dyes and Pigments | 2015

Differently linked fluorene-carbazole triads for light amplification

Paulius Baronas; Karolis Kazlauskas; Gediminas Kreiza; Vygintas Jankauskas; Ausra Tomkeviciene; Jurate Simokaitiene; S. Grigalevicius; Juozas V. Grazulevicius; Saulius Jursenas


Dyes and Pigments | 2015

Impact of non-symmetric 2,9,10-aryl substitution on charge transport and optical properties of anthracene derivatives

Tomas Serevičius; Povilas Adomėnas; Ona Adomėnienė; Karolis Karpavičius; Jonas Bucevicius; Regimantas Komskis; Gediminas Kreiza; Vygintas Jankauskas; Karolis Kazlauskas; S. Juršėnas


Tetrahedron | 2012

Facile synthesis of spiro[benzo[e]indole-2,2′-piperidine] derivatives and their transformation to novel fluorescent scaffolds

Vida Buinauskaitė; Vytas Martynaitis; Sven Mangelinckx; Gediminas Kreiza; Norbert De Kimpe; Algirdas Šačkus


Physical Chemistry Chemical Physics | 2017

Structure–property relationship of blue solid state emissive phenanthroimidazole derivatives

Agne Ivanauskaite; Ramunas Lygaitis; Steponas Raisys; Karolis Kazlauskas; Gediminas Kreiza; Dmytro Volyniuk; Dalius Gudeika; Saulius Jursenas; Juozas V. Grazulevicius

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Algirdas Šačkus

Kaunas University of Technology

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Aurimas Bieliauskas

Kaunas University of Technology

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