Date: 2025-05-20
New Paper!
S. Pazylbek, J. Stadulis, G. Doke, A. Antuzevics, V. Pankratov, G. Merkininkaite, A. Katelnikovas, A. Zarkov, Tunable broadband visible emission achieved by phase transformation-driven self-reduction of Eu3+ to Eu2+ in a calcium phosphate matrix, Dalton Transactions 54(21) (2025) 8625-8634.
Abstract:
In this work, we report the synthesis of Eu2+-doped alpha-tricalcium phosphate (α-TCP, α-Ca3(PO4)2) via a phase transformation of Eu3+-doped CaHPO4·2H2O. The phase conversion accompanied by a reduction of Eu3+ to Eu2+ occurred during the annealing of the starting material in a vacuum. The optical properties of the obtained α-TCP:Eu2+ were investigated by photoluminescence (PL), thermally stimulated luminescence, and persistent luminescence decay measurements. The obtained material exhibited tunable broadband PL with FWHM values ranging from 87 to 142 nm at room temperature. The PL can be tuned in terms of emission maximum and FWHM by varying the excitation wavelength. The broadband emission was achieved due to the multi-site occurrence of Eu2+ ions in the complex α-TCP matrix. Three types of traps were determined with activation energy values of 0.80, 0.75, and 0.68 eV. After irradiation with X-rays, an afterglow characterizable by an Eu2+ broadband spectrum with a maximum at around 480 nm can be detected for at least 10 h.
Link: https://pubs.rsc.org/en/content/articlelanding/2025/dt/d5dt00681c
Date: 2024-12-13
New Paper!
S. Pazylbek, J. Stadulis, G. Doke, A. Antuzevics, M. Sandomierski, A. Katelnikovas, C.-Y. Su, H.‑W. Fang, A. Zarkov, Luminescent properties of near-infrared-emitting Cr3+-activated beta-Ca3(PO4)2, Optical Materials 159 (2025) 116569.
Abstract:
In this study, we present a novel dissolution-precipitation approach for the synthesis of rhabdophane-type GdPO4·nH2O nanostructures using amorphous calcium phosphate (ACP) as a precursor. It was shown that in aqueous medium in the presence of Gd3+ ions ACP can be successfully converted to GdPO4·nH2O. We systematically investigated the effects of synthesis duration, P-to-Gd molar ratio in the reaction mixture, synthesis temperature, and hydrothermal reactor filling volume on the phase composition and morphology of the obtained products. The samples were analyzed using powder X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Furthermore, the assessment of the specific surface area (SBET) and magnetic properties of the selected samples was performed. The GdPO4·nH2O particles prepared under certain synthesis conditions were characterized by notably high SBET values reaching up to 157 m2g⁻1.
Link: https://doi.org/10.1016/j.optmat.2024.116569
Date: 2024-11-10
New Paper!
E. Butkevic, E. Raudonyte-Svirbutaviciene, K. Mazeika, V. Pankratov, A.I. Popov, A. Kareiva, A. Zarkov, Amorphous Calcium Phosphate as a Precursor for the Synthesis of GdPO4·nH2O Nanostructures, Ceramics International (2024) https://doi.org/10.1016/j.ceramint.2024.11.153.
Abstract:
In this study, we present a novel dissolution-precipitation approach for the synthesis of rhabdophane-type GdPO4·nH2O nanostructures using amorphous calcium phosphate (ACP) as a precursor. It was shown that in aqueous medium in the presence of Gd3+ ions ACP can be successfully converted to GdPO4·nH2O. We systematically investigated the effects of synthesis duration, P-to-Gd molar ratio in the reaction mixture, synthesis temperature, and hydrothermal reactor filling volume on the phase composition and morphology of the obtained products. The samples were analyzed using powder X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Furthermore, the assessment of the specific surface area (SBET) and magnetic properties of the selected samples was performed. The GdPO4·nH2O particles prepared under certain synthesis conditions were characterized by notably high SBET values reaching up to 157 m2g⁻1.
Link: https://doi.org/10.1016/j.ceramint.2024.11.153
Date: 2024-04-04
New Paper!
E. Kabasinskas, D. Karoblis, D. Griesiute, E. Raudonyte-Svirbutaviciene, S. Pazylbek, R. Lemezis, V. Klimavicius, A. Kareiva, A. Zarkov, Synthesis and morphological control of Ca5(PO4)3Cl and Ca2PO4Cl via the phase transformation of amorphous calcium phosphate in molten chlorides, Ceramics International 50(10) (2024) 16844-16851.
Abstract:
In the present work, the phase conversion of amorphous calcium phosphate (ACP) in different molten chlorides (LiCl, NaCl, KCl, CaCl2) was investigated in detail. The main synthesis parameters influencing the phase purity and morphological features of the products include the chemical composition of molten salts, the heat treatment temperature and the ACP-to-flux ratio. The selective synthesis of single-phase Ca5(PO4)3Cl or Ca2PO4Cl depends on the content of CaCl2 in the reaction medium. The morphology control of Ca5(PO4)3Cl powders was achieved by varying the KCl/CaCl2 ratio in the flux, resulting in the formation of the particles of different size and shape. The KCl-rich fluxes led to the formation of relatively small nearly spherical particles, whereas the CaCl2-rich fluxes promoted an anisotropic growth of the Ca5(PO4)3Cl crystals resulting in the formation of monodispersed hexagonally-shaped microrods. Whereas the anisotropic growth was observed at relatively low temperature (750 °C) the increase of the reaction temperature up to 1200 °C significantly reduced this effect leading to the formation of the particles with obviously low aspect ratio. The phase crystallinity and purity were analyzed using powder X-ray diffraction, FTIR spectroscopy as well as 31P, 35Cl and 1H solid-state NMR. The morphological features and chemical composition of the synthesized products were studied by SEM/EDX analysis.
Link: https://doi.org/10.1016/j.ceramint.2024.02.157
Date: 2023-10-18
New Paper!
A. Afonina, A. Dubauskas, V. Klimavicius, A. Zarkov, A. Kareiva, I. Grigoraviciute, Phase transformations during the dissolution-precipitation synthesis of magnesium whitlockite nanopowders from gypsum, Ceramics International 49(23, Part A) (2023) 38157-38164.
Abstract:
In the present work, magnesium whitlockite (Mg-WH) powders were synthesized via a low-temperature dissolution-precipitation process using gypsum as a starting material. The suggested synthetic approach is cost-effective and environmentally friendly solution, promoting sustainable manufacturing practises. The phase evolution and formation of Mg-WH in an aqueous medium in the presence of magnesium and phosphate ions under static and rotating conditions were investigated. Powder XRD patterns, FTIR spectra and SEM images were obtained for samples synthesized for different times to monitor the gradual phase transformation. It was found that single-phase Mg-WH can be obtained using both synthetic approaches, however, the reaction under rotating conditions favors faster formation of Mg-WH crystals. Samples obtained under static conditions had larger crystallite size and higher crystallinity, while those prepared under rotating conditions had smaller crystallites and lower crystallinity. The Rietveld refinement confirmed the structural parameters of the synthesized samples, indicating a slight change in the lattice parameters and magnesium occupancy with an extended synthesis time. We state that the phase composition, crystallite size, crystallinity, and powder morphology can be facilely controlled by regulating the synthesis time and selecting the synthesis setup.