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Lyubomir Aleksandrov

Lyubomir Aleksandrov

PhD

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60
Publications
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563
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Publications

Publications (60)
Article
Homogenous and transparent 50ZnO:40B2O3:10WO3:xEu³⁺, x = 0, 0.1, 0.5, 1, 2, 5 and 10 mol% glasses were obtained by melt quenching method. Their crystallization behavior was studied by Differential Thermal Analysis (DTA) and X-ray Diffraction Analysis (XRD) measurements. It was established the formation of ZnWO4 as a single crystalline phase after t...
Article
Dy³⁺ doped glasses from the oxide system CaOGeO2Li2OB2O3 with different compositions were prepared by melt quenching technique. The obtained glass samples were characterized by X-ray diffraction (XRD), Differential thermal analyses (DTA), Infrared spectroscopy (IR) and Photoluminescence (PL) measurements. The X-ray analysis reveals amorphous nature...
Article
This work presents results on nanosecond laser-induced surface structuring of AlN ceramic. The process under investigation is performed using the fundamental wavelength of Nd:YAG laser system. It is shown that the change of the ambient air pressure from atmospheric one to 10⁻⁴ Torr, leads to modification of the surface morphology – from ripples str...
Article
Europium doped glasses with three different compositions and different dopant concentrations were prepared from the CaO-GeO2-Li2O-B2O3 system. The influences of Eu³⁺ ions concentration on the thermal stability of the glasses were investigated by DTA analyses. The IR spectra display variations in the glass structures depending on the glass compositi...
Article
Full-text available
In this work, the ablation rate and surface modifications are studied of aluminum nitride ceramic treated by a pulsed nanosecond Nd:YAG laser at four wavelengths—266 nm, 355 nm, 532 nm, and 1064 nm. The ablation depth is presented as a function of the laser fluence and the number of pulses applied. A decrease of the ablation efficiency with the inc...
Article
Full-text available
Terbium doped glasses with three different compositions from the system CaO-GeO2-Li2O-B2O3 and different dopant concentrations were prepared. DTA analyses show weak influence of the rare earth ion on the glass thermal properties. The FTIR spectra revealed variations between glass structures. Excitation and emission spectra of the doped glasses poss...
Article
Eu³⁺ doped glasses and partially crystalized materials of 50ZnO:(50-x)B2O3:xWO3, x = 0, 10, 15, 20 mol% were synthesized by melt quenching. X-ray amorphous samples were prepared from the base binary composition 50ZnO:50B2O3 and from ternary composition containing 10 mol% WO3. By visual observation, phase separation in the binary zinc borate glass w...
Article
Full-text available
In this work, results on a new laser-induced mechanism of microstructures formation on the surface of borosilicate glass are presented. The samples are fabricated by melt quenching method and consist of 50% SiO2, 20% Al2O3, 20% B2O3, 5% CaO, 2% Li2O, 3% MgO (in wt.%). Irradiation at 266 nm delivered by Nd:YAG nanosecond system is used to modify the...
Article
Full-text available
The paper presents results on femtosecond laser irradiation-induced modification of the optical properties of a composite material – gold nanoparticles embedded into a borosilicate glass host. The process is initiated by laser pulses delivered by a Ti:sapphire laser system with pulse duration of 35 fs. The glass samples are prepared by melt quenchi...
Article
This paper describes the luminescence properties of small silver clusters formed by laser treatment of silver-doped borosilicate glass. Using irradiation by a Nd:YAG nanosecond laser system operating at the fourth harmonic wavelength (266 nm), areas are formed in the glass samples that emit bright luminescence peaking at about 600 nm when excited b...
Article
The process of laser radiation-induced formation and decomposition of Ag nanoparticles in glass is studied. Borosilicate glass samples are fabricated by melt quenching method. Silver nitrate is added in the fabrication stage in amount to form final glass samples with compositions of 1, 1.5, 5, and 10 wt% Ag. The fabricated samples are irradiated by...
Article
Glasses of (100-(x + y))·(0.6B 2 O 3 ·0.4Bi 2 O 3)·xLa 2 O 3 ·yWO 3 , x = 0, 10; y = 0 ÷ 40 mol% were prepared by melt quenching. Density measurements, thermal analysis, UV-vis diffuse reflectance spectroscopy, X-ray photoelec-tron spectroscopy and theoretical modeling using Density Functional Theory were employed to identify the effect of WO 3 con...
Article
This work represents results on the response of noble metal-doped borosilicate glass to laser radiation with femto- and nanosecond pulse duration. The material under study is obtained by conventional melt quenching method as samples with noble metal concentration varied up to 10 wt% are fabricated. Optical and morphology changes of the glass sample...
Article
Noble metal nanoparticle composed glasses attract significant attention due to the unique optical properties that they express in the near UV and visible spectral range. These are related to the high values of the extinction cross section and nonlinear optical characteristics. In this work we study the ability of laser irradiation to induce modific...
Article
Full-text available
We present results on laser-induced color changes in gold- and silver-doped glass. The doped borosilicate glass was prepared by conventional melt quenching. The study was focused on the change of the optical properties after irradiation of the glass by femtosecond laser pulses. Under certain conditions, the laser radiation induces defects associate...
Article
Full-text available
Amorphous hybrid materials with participation of water soluble biopolymer (pectin from apple-AP) and silica derived from tetraethoxy silane (TEOS) were synthesized by sol–gel method. The influence of biopolymer content was determined. The principles of the hybrids formation were developed using structural data from Fourier transform infrared spectr...
Article
New multicomponent (100 − (x − y))·(0.6B2O3·0.4Bi2O3)·xLa2O3·yWO3, x = 0, 10; y = 0 ÷ 40 mol% glasses were obtained by melt quenching technique and its structure were examined by infrared and Raman spectroscopies. Based on the obtained spectral data it was suggested that in the absence of La2O3, tungsten incorporates into boro-bismuthate network in...
Article
In this work the effects of laser radiation and annealing process on the change of the optical properties of gold doped borosilicate glass are presented. The glass is fabricated by conventional melt quenching method as samples with three different concentrations of gold are produced. The laser irradiation is performed by a Nd:YAG system that genera...
Article
Full-text available
The study focused on sol-gel synthesis of biopolymer-silica hybrids further used as materials for laccase immobilization. Silica was obtained from tetraethyl orthosilicate (TEOS), while pectin, derived from citrus fruits, was used as a biopolymer. The structure of the hybrids obtained was investigated by X-ray diffraction, Fourier transform infrare...
Article
Full-text available
We present results on laser-assisted formation of two- and three-dimensional structures comprised of gold nanoparticles in glass. The sample material was gold-ion-doped borosilicate glass prepared by conventional melt quenching. The nanoparticle growth technique consisted of two steps – laser-induced defect formation and annealing. The first step w...
Article
BaO-TeO2 glasses containing 10 to 20-mol% BaO were studied by X-ray diffraction, density, thermal analysis, UV-visible and Raman spectroscopy. The effects of Eu³⁺, Dy³⁺, Er³⁺ and Nd³⁺ on the density, thermal, optical absorption and luminescent properties of barium tellurite glasses were studied. The short-range structure of barium tellurite glasses...
Article
Single phase nanosized NiFe2O4 powders were prepared by a solution combustion method with the use of four different types of fuel (two of them containing nitrogen and the other two - pure hydrocarbons). The resulting materials were characterized with respect to structural and morphological features by using appropriate methods. Magnetization curves...
Article
Full-text available
Reduced graphene oxide-silicate (RGO/SiO2) nanocomposites were prepared by a sol-gel method by mixing 10 wt% and 20 wt% of RGO with tetraethyl orthosilicate (TEOS). RGO sheets were prepared by chemical exfoliation of purified natural graphite powder. The phase formation and the structural transformations of the samples are verified by X-ray diffrac...
Article
Lignin-copper based composite materials have been successfully prepared by saturated steam and water bath. The structural and thermal parameters have been done. Significant decreases in the intensity of the O-H absorption band at 3430 cm⁻¹ can be connected with reduced content of free hydroxyl group in the biopolymer after modification due to coord...
Conference Paper
Glass and glass-crystalline materials with nominal composition 55B(2)O(3)center dot 35Bi(2)O(3)center dot 10La(2)O(3) doped with 1 mol% EU2O3 were synthesized by melt quenching method. Different phases were developed, applying several melting temperatures. According to the XRD data, glass-crystalline materials containing LaBO3 as crystalline phase...
Article
The glasses with the nominal compositions of (50 - x)MoO3-xWO3-25La2O3-25B2O3 with x = 0, 10, 20, 30, 40, and 50 (mol%) were prepared using a conventional melt quenching method and their structure and crystallization behavior were investigated from Raman scattering spectroscopy, infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), an...
Research
Full-text available
Mineral trioxide aggregate (MTA) is based on plain Portland cement and is composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium alumoferrite. This cement is used for various dental clinical applications. The degree of solubility of calcium-silicate based cements is an object of debate among investigators. The p...
Article
Full-text available
Graphene is very attractive material which has strong conductivity and electrical properties. By using the glass as a matrix to incorporate the graphene, it is possible to improve the conductivity and the electrical properties of the glass. In our previous study we synthesized composite material by adding of reduced graphene oxide (RGO) to silica [...
Article
Full-text available
This article presents data referring to the mechanochemical activated synthesis of amorphous and crystalline LaBWO 6. A stoichiometric mixture of La 2 O 3 , B 2 O 3 and WO 3 of a 1:1:2 molar ratio was subjected to intense mechanical treatment in air using a planetary ball mill (Fritsch-Premium line-Pulversette No. 7). The obtained samples were anal...
Article
The glass formation region in the section 90(xZnO.yWO3.zLa2O3).10Al2O3 of a constant Al2O3 content of 10 mol % and varying amounts of WO3, ZnO and Nd2O3 from ZnO-WO3-La2O3-Al2O3 system is determined by the melt quenching technique (with cooling rates of 10 Ks-1 - 102 Ks-1). The glasses are obtained from compositions of a high WO3 content (60 mol %...
Article
The structure of many Eu3+ doped Bi2O3-B2O3-WO3-Al2O3 glasses of a different composition is studied using infrared spectroscopic technique (IR). It is found that distorted BiO6 (of a band at 480 cm-1), BO3 (of bands at 1390, 1230, 620 cm-1), BO4 (of a band at 1020 cm-1) and WO4 polyhedra (of a band at 880 cm-1) are the main building units forming t...
Chapter
Full-text available
In a previous paper (Shalaby A, Yaneva V, Staneva A, Aleksandrov L, Iordanova R, Dimitriev Y, Nanoscience & nanotechnology – nanostructured materials application and innovation transfer (14), ISSN 1313-8995, 2014) we studied reduced graphene oxide (RGO)/SiO2 composite material by adding a small amount of RGO to silica in order to avoid the aggregat...
Data
Full-text available
Abstract: Graphene the wonder material has attracted of a great deal of scientific interest in recent years. Graphene and its composites have been applied in the fields of nanoelectronic devices, transparent conductors, biosensors, photothermal therapy and drug delivery. Thermal stability is an important property of graphene required to be investig...
Article
Full-text available
Graphene the wonder material has attracted of a great deal of scientific interest in recent years. Graphene and its composites have been applied in the fields of nanoelectronic devices, transparent conductors, biosensors, photothermal therapy and drug delivery. Thermal stability is an important property of graphene required to be investigated due t...
Article
In WO3–La2O3–B2O3 system, glasses were obtained in the region between 20 and 30 mol% La2O3. A liquid-phase separation region was observed near the WO3–B2O3 side. A glass with nominal composition 50WO3:25L2O3:25B2O3 doped with Eu2O3 was synthesized by melt quenching method. The obtained glass was characterized by X-ray diffraction (XRD), differentia...
Article
Full-text available
Molybdenum oxide (MoO3) is known to be only slightly soluble in borate and borosilicate glasses inducing liquid phase separation in supercooled melts during cooling. The goal of this study is to verify the tendency to immiscibility and crystallization in multicomponent compositions of the system SiO2–B2O3–Na2O–ZnO–Nd2O3–MoO3, in which the content o...
Article
In this work we focus on the comparison of the structure, thermal stability and crystallization behavior of MeO3-La2O3-B2O3 glasses (Me=Mo and W). The amorphous materials are prepared by a conventional melt quenching method. The thermal parameters are determined by differential thermal analysis (DTA), and the crystalline phases obtained after heat...
Article
Glasses with the nominal compositions of xWO325La2O3(75−x)B2O3 (mol%) with x=15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical...
Article
The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi2O3–MoO3–B2O3. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microsc...
Article
The glass formation region in the ternary ZnO―Bi2O3―WO3 system is determined by melt quenching technique (cooling rates 101–102 K/s). New original glasses are obtained in a narrow concentration range with high WO3 content (60–75 mol%). Homogeneous glasses of the composition (100 − x)[0.2ZnO·0.3Bi2O3·0.5WO3]xMoO3, were obtained between 20 and 60 mol...
Article
The purpose of this paper is to study the glass formation tendency in the ternary system B2O3―Bi2O3―MoO3 and to define the main structural units building the amorphous network. A wide glass formation area was determined which is situated near the Bi2O3―B2O3 side. A liquid phase separation region was observed near the MoO3―B2O3 side for compositions...
Article
The ternary MoO3–La2O3–B2O3 glasses containing a large amount of MoO3 (10–50mol%) are prepared, and their structure and crystallization behavior are examined from the Raman scattering spectrum measurements and X-ray diffraction analyses. It is found that the glass transition and crystallization temperatures and the thermal stability against crystal...
Article
Molybdenum oxide (MoO3)-containing glasses of xMoO3–50ZnO–(50−x)B2O3 (x=10, 20, and 30) are prepared using a conventional melt quenching method, and the glass structure and crystallization behaviour are clarified. It is found that the thermal stability against crystallization of the glasses decreases drastically with increasing MoO3 content. The ma...
Article
In this study, we focus on the structure and crystallization behavior of MoO3-La2O3-B2O3 and MoO3-ZnO-B2O3 glasses. Glasses of both systems were prepared by a melt-quenching method. The thermal stability of the glasses was examined using differential thermal anaysis (DTA) measurements, and the crystalline phases formed by heat treatments were ident...
Article
The aim of the present work is to verify the synthesis of bismuth borates by crystallization from glasses. Several bismuth boromolybdate glasses were selected and heat treated at 500-530 °C for different exposure times. Obtaining of BiBO3 polymorphs, Bi4B2O 9, Bi3B5O12 and Bi 2MoO6 has been detected by X-ray diffraction (XRD). Additional informatio...
Article
In MoO3–Nd2O3–B2O3 and MoO3–Nd2O3–La2O3–B2O3 systems, glasses were obtained in the region between 20 and 30 mol% Ln2O3. A liquid-phase separation region was observed near the MoO3–B2O3 side up to 20 mol% Ln2O3 (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spect...
Article
Full-text available
Glasses in the MoO3-La2O3-B2O3 and MoO3-Nd2O3-B2O3 systems were obtained between 20 and 40 mol% Ln2O3 (Ln=La, Nd). A liquid phase separation region was observed near the MoO3-B2O3 side for compositions containing below 20 mol% Ln2O3. New original glasses containing between 45 and 70 mol% ZnO were prepared in the MoO3-ZnO-B2O3 system. The amorphous...
Article
The title compound, dineodymium(III) tris[tungstate(VI)], is a member of the Eu2(WO4)3 structure family and crystallizes isotypically with other rare earth tungstates and molybdates of this formula type. The structure is a derivative of the scheelite (CaWO4) structure and can be considered as an ordered defect variant with a threefold scheelite sup...
Article
Low melting glasses in the MoO3-Nd2O3-Bi2O3 system were obtained at slow (102 K/s) and high cooling rates (104-105 K/s). The amorphous state of the samples was proved by X-ray diffraction. Comparative analysis of the infrared spectra of the obtained glasses and other available molybdate spectral data was carried out. The structure of glasses with a...
Article
Novel low melting glasses in the MoO3-La2O3-Nd2O3 system were obtained at different cooling rates (102 K/s and 104-105 K/s). Characterization of the amorphous samples was made by differential thermal analysis (DTA) and X-ray absorption fine structure (XAFS) method. According to DTA data of the glass samples, the glass transition temperatures are at...
Article
Novel low melting glasses in the MoO3-La2O 3-Nd2O3 system were obtained at different cooling rates (102 K/s and 104-105 K/s). Characterization of the amorphous samples was made by differential thermal analysis (DTA) and X-ray absorption fine structure (XAFS) method. According to DTA data of the glass samples, the glass transition temperatures are a...
Article
Low melting glasses in the MoO3-Nd2O 3-Bi2O3 system were obtained at slow (10 2 K/s) and high cooling rates (104-105 K/s). The amorphous state of the samples was proved by X-ray diffraction. Comparative analysis of the infrared spectra of the obtained glasses and other available molybdate spectral data was carried out. The structure of glasses with...

Projects

Projects (3)
Project
The main goal of the project is preparation of new glass-ceramic luminescent materials, containing Ca2GeO4, Li2CaGeO4 or Ca5Ge3O11 phases doped by Tb3+, Eu3+ and Dy3+ ions. The planed studies are pioneer since obtaining of oxide glass-ceramic with luminescent properties from germanate systems has not been described in the literature. The problem is actual because finding of new promising luminescent materials is relevant to ecology, energy saving and improvement of the human life.
Project
The main aim of the project is to obtain new multicomponent glasses in the systems WO3-La2O3-B2O3-Nb2O5 and WO3-ZnO-B2O3-Nb2O5 doped with Eu3+, as a transparent active media for optical application. The actuality of this research is determined by the urgent need of new matrixes for light-emitting diodes (led). Compared to the conventional light sources, LEDs are one of today's most energy-efficient, environmental friendly and rapidly developing lighting technologies, which has the potential to fundamentally change the future of lighting.
Archived project
Main research goals in the project: - development of a method for laser induced formation of 3D noble metal nanoparticle ensembles in glass materials; - understanding the role of the material composition and experimental conditions of laser and heat treatment on the spatial properties of the structures; - fabrication of 3D noble metal nanoparticle structures and description of their optical properties. Bulgarian Academy of Sciences: Institute of Electronics, Institute of Solid State Physics, Institute of General and Inorganic Chemistry