arXiv subjects

Vojtech Vanecek

Publications and source records attributed to Vojtech Vanecek.

7 recordsLinked to original sources

arXiv2026

In-depth study of spectroscopic properties of new $Pr^{3+}$-ion doped low-phonon sesquisulfide $Lu_2S_3$ material for mid-IR laser sources

$Lu_2S_3$ material from the family of sesquisulfide hosts appears to be a promising low-phonon material for use as a laser gain medium allowing for a laser emission over a broad spectral range from ultraviolet to far mid-infrared wavelengths. In this paper, a praseodymium-ion doped $Lu_2S_3$ single crystal grown by micro-pulling down technique is investigated with focus on its spectroscopic properties. The Raman, excitation, and luminescence spectra are presented. By selective excitation of the main energy levels of $Pr^{3+}$-ions, 26 luminescence transitions of the $Pr:Lu_2S_3$ crystal spanning the 0.49 to 5.5 $\mu$m wavelength range have been identified. The correct assignment of the observed luminescence spectra to the respective $Pr^{3+}$ energy-level transitions was confirmed by the calculation of the optimized squared reduced-matrix elements for the tensor operators U(k) and L + gS.

cond-mat.mtrl-sci↗

arXiv2026

Optimized Photoemission from Organic Molecules in 2D Layered Halide Perovskites

In recent years, hybrid organic-inorganic metal halides have been at the forefront of materials research. Typically, the functional (e.g., optoelectronic) properties of hybrid halides are derived from the inorganic structural part, whereas the organic structural units can add extra advantages in terms of stability, rigidity, and processability. Here, we report the design, synthesis, and characterization of two new hybrid materials in which the outstanding photophysical properties originate from the organic structural part. The new compounds, (C15H16N)2CdCl4 and ((Br)C15H15N)2CdCl4, have 2D layered Ruddlesden-Poppertype perovskite structures. These hybrids are blue-white light emitters just like their corresponding pure organic salts, but with much improved emission efficiencies. Optical spectroscopy and density functional theory (DFT) studies confirm that photoemission comes from the trans-stilbene organic cations. The photoluminescence quantum yield (PLQY) values of these new materials are among the highest known, 50.83 % and 26.60 % for (C15H16N)2CdCl4 and ((Br)C15H15N)2CdCl4, respectively. This is up to a 5-fold increase as compared to the light emission efficiency of the precursor salt C15H16NCl (PLQY of 10.33 %). Alongside their outstanding optical properties, their environmental and thermal stability allow their consideration for potential practical applications such as radiation detection. This work shows that hybrid metal halides can be compositionally and structurally engineered to have highly efficient photoemission originating from the organic components for fast scintillation applications.

cond-mat.mtrl-sci↗

arXiv2026

Bridgman method grown $Cs_2Li_3I_5$: an inter-alkali metal scintillator with high lithium content

In this study, we report on the growth of ternary caesium lithium iodide ($Cs_2Li_3I_5$, CLI) bulk crystals, both undoped and doped with thallium (Tl) and indium (In), using the miniaturised vertical Bridgman method (mVB). X-ray Powder Diffraction (XRPD) confirmed the presence of the ternary CLI phase in all three crystals, with CLI : In appearing homogeneous structure-wise throughout the entire ingot. Measurements of radioluminescence (RL), photoluminescence emission (PL), photoluminescence excitation (PLE) spectra, and photoluminescence decay kinetics (PL decay) demonstrated that the primary luminescence centers originate from the matrix itself. When doped with thallium, the efficiency of the luminescence was significantly increased. Furthermore, CLI : Tl and CLI : In crystals exhibited emission spectra similar to those of their doped caesium iodide counterparts, CsI : Tl and CsI : In, respectively. The main component of the PL decay was 523 ns, 557 ns, and 554 ns for the undoped, Tl+-doped, and In+-doped crystals, respectively. It is worthy of note that only CLI : Tl exhibited a single exponential decay. Differential Scanning Calorimetry (DSC) measurements revealed two endothermic peaks corresponding to the eutectic and liquidus temperature for CLI and CLI : In, indicating that this ternary compound has a congruent melting behaviour. Finally, the melting point of CLI was estimated to be approximately 220 {\deg}C.

cond-mat.mtrl-sci↗

arXiv2024

Advanced Halide Scintillators: From the Bulk to Nano

Halide scintillators play a crucial role in the detection of ionizing radiation since the discovery of scintillation in NaI:Tl in 1948. The discovery of NaI:Tl motivated the research and development (R&D) of halide scintillators resulting in the development of CsI:Tl, CsI:Na, CaF$_2$:Eu, etc. Later, the R&D shifted toward oxide materials due to their high mechanical and chemical stability, good scintillation properties, and relative ease of bulk single crystal growth. However, the development in crystal growth technology allowed for the growth of high-quality single crystals of hygroscopic and mechanically fragile materials including SrI$_2$ and LaBr$_3$. Scintillators based on these materials exhibit excellent performance and push the limits of inorganic scintillators. These results motivated intense research of a large variety of halide-based scintillators. Moreover, materials based on lead halide perovskites found application in the fields of photovoltaics, solid-state lighting, and lasers. The first studies show also the significant potential of lead halide perovskites as ultrafast scintillators in the form of NCs. The purpose of this review is to summarize the R&D in the field of halide scintillators during the last decade and to highlight perspectives for future development.

physics.app-ph↗

arXiv2024

Ultraviolet cross-luminescence in ternary chlorides of alkali and alkaline-earth metals

After the discovery of a cross-luminescence (CL) in BaF2 in 1982, a large number of CL scintillators were investigated. However, no CL scintillator superior to BaF2 has been discovered, and the research of CL scintillators has subsided. Recent technological development in medical imaging and high-energy physics created a new demand for ultra-fast scintillators further supported by the development of UV-sensitive semiconductor photodetectors. As a consequence, renewed interest in CL scintillators appeared. To satisfy the requirements of fast timing applications high photo-detection efficiency, e. i. a good spectral match between the scintillator and photodetector must be achieved. Cesium-based ternary chlorides could provide a red-shift (~1.5 eV) of CL towards the sensitive region of the photodetector (PMT or SiPM) while keeping light output and timing characteristics comparable to BaF2.

physics.ins-det↗

arXiv2024

Growth and Spectroscopic Properties of Pr$^{3+}$ Doped Lu$_2$S$_3$ SingleCrystals

For the first time Lu$_2$S$_3$ (undoped and Pr-doped) single crystals were successfully grown from melt using micro-pulling-down (mPD) technique. Customization of halide mPD apparatus allowed us to grow rod-shaped (\O 2 mm and length around 20 mm) crystals of Lu$_2$S$_3$ with high melting temperature (~1750 $^\circ$C). X-ray powder diffraction revealed that the grown crystals exhibit the {\epsilon}-Lu$_2$S$_3$ crystal structure ($\alpha$-Al$_2$O$_3$ type, space group R-3c). Optical and scintillation properties of both the undoped and Pr$^{3+}$ doped Lu$_2$S$_3$ were investigated. Fast 5d-4f Pr$^{3+}$ luminescence was observed in both photoluminescence and radioluminescence spectra. The presented technology is an effective tool for the exploration of a large family of high-melting sulfides. Such materials show promise for application as scintillators, active laser media, and optoelectronic components.

cond-mat.mtrl-sci↗

arXiv2024

Li$_2$MnCl$_4$ single crystal: new candidate for red-emitting neutron scintillator

Novel red-emitting scintillator Li$_2$MnCl$_4$ is proposed as a candidate for thermal neutron detection. It features high Li content, low density, low effective atomic number, and emission in red-NIR region. These characteristics make it an interesting candidate for long distance neutron detection in harsh enviroments e. g. decomisioning of nuclear powerplants. The absorption spectrum is thoroughly investigated in the scope of Tanabe-Sugano diagram. Luminescence mechanism in the undoped Li$_2$MnCl$_4$ is studied in depth. Doping by Eu$^{2+}$ and Ce$^{3+}$ is introduced as a trial to improve the scintillation efficiency. We show in the Eu$^{2+}$ and Ce$^{3+}$ doped Li$_2$MnCl$_4$ that luminescence mechanism involves energy transfer from the dopants to Mn$^{2+}$, and propose the local lattice distortion around the dopant and a possible charge compensation mechanisms.

cond-mat.mtrl-sci↗