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Solid state NIR-to-visible photon upconversion (UC) mediated by triplet–triplet annihilation (TTA) is necessitated by numerous practical applications. Yet, efficient TTA-UC remains a highly challenging task. In this work palladium phthalocyanine-sensitized NIR-to-vis solid UC films based on a popular rubrene emitter are thoroughly studied with the primary focus on revealing the impact of t-butyl substitution in rubrene on the TTA-UC performance. The solution-processed UC films were additionally doped with a small amount of emissive singlet sink tetraphenyldibenzoperiflanthene (DBP) for collecting upconverted singlets from rubrene and in this way diminishing detrimental singlet fission. Irrespective of the excitation conditions used, t-butyl-substituted rubrene (TBR) was found to exhibit enhanced TTA-UC performance as compared to that of rubrene at an optimal emitter doping of 80 wt% in polystyrene films. Explicitly, in the TTA dominated regime attained at high excitation densities, 4-fold higher UC quantum yield (ΦUC) achieved in TBR-based films was caused by the reduced fluorescence concentration quenching mainly due to suppressed singlet fission. Under low light conditions, i.e. in the regime governed by spontaneous triplet decay, even though triplet exciton diffusion was obstructed in TBR films by t-butyl moieties, the subsequently reduced TTA rate was counterbalanced by both suppressed singlet fission and non-radiative triplet quenching, still ensuring higher ΦUC of these films as compared to those of unsubstituted rubrene films.

We have deposited a series of ALD oxides HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 , SiO 2 , Al 2 O 3 within same reactor and prepared as GaN-MOS structure. A comprehensible diverse distribution of flat-band voltage depending on two different deposition temperatures 100-125°C and 250-300°C, and oxidant H 2 O or O 3 was obtained. At zero gate voltage and under unstressed condition we have observed a qualitative feature demonstrating different dependence of the net fixed charge in the oxide or/and at the interface with the deposition temperature, namely, an increase of positive charge for oxidant water oxide and an increase of negative charge for oxidant ozone oxide. Best interface quality, least charge only slightly influenced by the deposition temperature, we have observed for the ZrO 2 /H 2 O (oxide/oxidant). Instead, highest deposition temperature dependence we have observed for the Al 2 O 3 /H 2 O.

Transition metal oxide films HfO2, ZrO2, Ta2O5, TiO2, Nb2O5, and Y2O3, together with Al2O3 and SiO2 for reference, were deposited by atomic layer deposition (ALD) and investigated. For all the films ALD process was performed within the same reactor at two temperature ranges 100–125∘C and 250–300∘C. Both water and ozone were used as oxygen sources if processes were available. Most films are amorphous as-deposited, but HfO2, ZrO2, and Y2O3 can be crystalline, depending on deposition temperature and oxygen source. After deposition and initial characterization, the films were annealed to different temperatures up to 1200∘C, depending on the material, to observe the crystallization process. When crystalline phases were observed, grain sizes have been derived from the X-ray diffractograms and compared with feature sizes in SEM images. RMS analysis revealed a general tendency - an increase of roughness with the appearance of crystallization. The temperature-dependent morphological investigations were supported by breakdown field measurements. Those are also strongly affected when a film becomes crystalline. Most values observed for break down fields agree with literature, some values exceed previously reported numbers.

Organic single crystals offering numerous advantages due to their long-range molecular order are considered a promising gain medium for realization of electrically-pumped organic lasers provided their amplified spontaneous emission (ASE) threshold is sufficiently low. Unfortunately, ASE thresholds of such crystals are typically more than one order of magnitude higher (in the range of tens of kW cm−2) as compared to those of amorphous neat/doped films. Here, this issue is addressed by rationally designing bifluorene-based compounds to express weak intermolecular coupling in the crystalline phase. The twisted molecular backbone as well as out-of-plane twisted dimethyl moieties attached at the fluorene end-groups additionally benefit with enhanced electron–vibronic coupling resulting in a large Stokes shift (0.5 eV) and reduced reabsorption of emission. Endowed with such features the bifluorenes exhibit similarly high radiative decay rates (≈1.5 × 109 s−1) when doped in polystyrene matrix at low concentrations and in sublimation-grown single crystals. The high radiative rates accompanied by excellent waveguiding properties, favorable orientation of transition dipole moments as well as non-overlapping excited-state absorption and gain regions enable achieving extremely low ASE thresholds (≈700 W cm−2) in the bifluorene single crystals. The achieved low threshold encourages employment of rationally designed molecules in organic crystals for lasing applications.