Excited-state absorption spectra of Pr³⁺ ions doped into LiY<inf>0.3</inf>Lu<inf>0.7</inf>F<inf>4</inf> mixed crystal

© 2016 Optical Society of America.The UV/visible polarized excited-state absorption (ESA) spectra from the 1D2 and 3Pj manifolds of 4f2-configuration of Pr3+ ions doped into LiY0.3Lu0.7F4 mixed crystal were studied at room temperature. The data about ESA cross-sections are necessary to estimate an efficiency of stepwise excitation of 4f5d-states of Pr3+ ions in these crystals

Investigation of gain characteristics in mixed crystals LiMeF4 (Me = Y, Lu, Yb) doped by Ce3+ ions

Differential gain spectra in the range 295-335 nm were measured in crystals of scheelite structure LiY1 - x Lu x F4 (x = 0-1), doped by Ce3+ ions. It is shown that variation of Lu 3+ and Y3+ ions relative content in LiY1 - x Lu x F4 crystals allows to manipulate the spectral width of the amplification band. Cross-sections of excited-state absorption at the wavelengths of Ce3+ luminescence, probability ratios of formation and thermal destruction of color centers depending on the Y3+ ions content in LiY1 - x Lu x F4 crystals were estimated. Even better gain characteristics have been demonstrated by LiLuF 4:Ce3+, doped by Yb3+ ions. The highest optical gain coefficient with a wide amplification band among studied samples was observed in LiLuF4:Ce3+ crystal, codoped by Yb 3+ ions. © 2014 Pleiades Publishing, Ltd

Room-temperature ferromagnetism in cerium dioxide powders

© 2015, Pleiades Publishing, Inc. Room-temperature ferromagnetism is detected in a CeO2 powder with a grain size of about 35 nm and a low (2 sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently

Photoconductivity and photodielectric effect in LiY1 - X Lu x F4 crystals doped with Ce3+ and Yb 3+ ions

Time and spectral dependences of the dielectric permittivity of the LiY1 - x Lu x F4 (x = 0, 0.5, and 1) crystals doped with Ce3+ and co-doped with Yb3+ ions under UV laser excitation were studied by the 8-mm microwave resonant technique at room temperature. The obtained photoconductivity spectrum in 240-310 nm spectral range was interpreted as a stepwise photoionization spectrum of the Ce 3+ ions due to sequential 4f-5d and 5d-6s transitions. Average lifetimes of free and defect trapped (color centers) charge carriers were estimated. © 2014 Pleiades Publishing, Ltd

The concept of fruit in the Gramineae and its use in the taxonomy of the family

O uso do termo "fruto" em Gramíneas é impreciso e inconsistente. Por ser seco, monospérmico, indeiscente e apresentar-se com o pericarpo aderido ao tegumento da semente e frequentemente confundido com esta. Algumas vezes, a unidade de dispersão, a espigueta e o antécio são confundidos com o fruto. O fruto das gramíneas é uma cariopse. Sua morfologia interna e externa encerram grande número de características passíveis de uso taxonômico. As classificações da cariopse atualmente existentes não são inteiramente satisfatórias.The use of the term "fruit" in relation to the Gramineae often lacks precision and consistency. Because it is a dry, monospermic, indehiscent type of fruit and because its pericarp is adherent to the seed coat, it is often mistaken for the seed. The unit of dispersal, the spikelet and the anthoecium are sometimes misinterpreted as the fruit. The basic grass fruit is the caryopsis and its internal and external morphological features represent a great source of evidence for taxonomic use. The existing classification of the caryopsis and research needs in the field are discussed

Color centers transient absorption and ultra-short pulse lasing from LiLu0.7Y0.3F4:Ce3+ active medium

© OSA 2015. We have obtained the single pulse laser oscillation with 400±10 ps pulse duration at 311 nm from LiLu0.7Y0.3F4:Ce3+ crystal due to passive Q-switch by means of pump induced color centers absorption. In this work we discuss the role of intrinsic transient color centers on losses dynamics

Ultra-short pulses UV lasing in multifunctional Ce:LiY<inf>0.3</inf>Lu<inf>0.7</inf>F<inf>4</inf> active medium

© 2016 Optical Society of America.The single pulse laser oscillation with 400 ± 10 ps pulse duration at 311 nm from LiY0.3Lu0.7F4:Ce3+ crystal was obtained from intracavity loss modulation via pump-induced color centers bleaching. Modulation of average losses is regulated via color centers concentration that determines the multifuncionality of solarizable LiY0.3Lu0.7F4:Ce3+ active medium

Pump-probe experiments with Ce3++Yb3+:KY 3F10 and Ce3++Yb3+:CaF2 crystals

Here we report on pump-probe studies of KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions. The crystals Ce3+:KY3F10 and Ce3+: CaF2 show attractive spectral characteristics for tunable UV lasers application but have poor photochemical stability. Their properties under intense UV pumping are affected by excited state absorption and color centers formation. This work was aimed at dynamic processes investigation induced by laser radiation of UV spectral range in KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions. Optical gain was observed on CaF2:Ce3++Yb3+ in the range 325-335 nm for the first time. It proves Yb3+ ions coactivation antisolarant effect elaborated by us earlier3. It is shown that in investigated crystals under a pump radiation, resonant to 4f-5d Ce3+ ions transitions several types of color centers (CC) are formed. Set of these CC types are determine the absorption at expected stimulated emission spectral range and magnitude of the induced loses is dependent on many factors. As a result of competition between CC formation, free charges recombination and CC photodestruction this balance can be shifted towards either rising or dropping losses at 5d-4f Ce3+ ions luminescence spectral range. © 2011 SPIE

Reconstruction of Transcription Control Networks in Mollicutes by High-Throughput Identification of Promoters

Bacteria of the class Mollicutes have significantly reduced genomes and gene expression control systems. They are also efficient pathogens that can colonize a broad range of hosts including plants and animals. Despite their simplicity, Mollicutes demonstrate complex transcriptional responses to various conditions, which contradicts their reduction in gene expression regulation mechanisms. We analyzed the conservation and distribution of transcription regulators across the 50 Mollicutes species. The majority of the transcription factors regulate transport and metabolism, and there are four transcription factors that demonstrate significant conservation across the analyzed bacteria. These factors include repressors of chaperone HrcA, cell cycle regulator MraZ and two regulators with unclear function from the WhiA and YebC/PmpR families. We then used three representative species of the major clades of Mollicutes (Acholeplasma laidlawii, Spiroplasma melliferum and Mycoplasma gallisepticum) to perform promoters mapping and activity quantitation. We revealed that Mollicutes evolved towards a promoter architecture simplification that correlates with a diminishing role of transcription regulation and an increase in transcriptional noise. Using the identified operons structure and a comparative genomics approach, we reconstructed the transcription control networks for these three species. The organization of the networks reflects the adaptation of bacteria to specific conditions and hosts

Thermal profiling of solid-state active media

© 2018 IEEE. The fluorescence intensity ratio technique to the thermal profiling of solid-state laser materials is developed. The temperature distribution inside the excited area of LiY0.8Yb0.2F4: Tm3+(0.2 at.%) crystals during z-scanning was studied