Vitali Nagirnyi

University of Tartu, Tartu, Estonia · Institute of Physics

Materials capable of emitting in the ultraviolet UV-C to UV-B spectral range have received considerable attention due to their potential applications in biophotonics, plant lighting, optical cleaning, sterilization, and disinfection. However, progress in the development of phosphors that emit in this short-wavelength range has been relatively slugg...

Luminescence properties of a palmieirite-type K5Eu(MoO4)4 crystal were studied in a wide temperature range of 7-650 K. Eu3+ ions are shown to occupy at least three non-equivalent positions in the...

A set of single-phase Cd1-xZnxWO4 (x = 0–1) solid solutions synthesized by spontaneous crystallization technique was studied by the methods of luminescence and electron paramagnetic resonance (EPR) spectroscopy. Luminescence spectra of all studied solutions are characterised by a single emission band related to the intrinsic emission of self-trappe...

Transparent light-converting Y3Al5O12:Ce (YAG:Ce) ceramics have become promising materials for advanced light-emitting diode and laser-driven white-light-generation technology. However, their functionality is highly dependent on factors such as structural quality, uniformity of dopant distribution, the presence of defects, and the cost of fabricati...

The luminescence properties of NASICON-type Na3.6M1.8(PO4)3 (M = Y, Lu) and Na3Sc2(PO4)3 phosphates, undoped and rare earth-doped (RE = Tb3+, Dy3+, Eu3+, Ce3+), were studied using synchrotron radiation in a wide energy region of 4.5–45 eV. Intrinsic emission originating from self-trapped excitons with electron component localized at the 3d Sc state...

The influence of preparation techniques on the structure and luminescent properties of K5Eu(MoO4)4 (KEMO) was investigated. KEMO phosphors were synthesized by three different techniques: solid state and sol-gel (sg) methods...

Short-wavelength synchrotron radiation excitation has been an indispensable tool in the studies of the properties of wide gap materials using time-resolved low-temperature luminescence spectroscopy. In recent years, several setups for such investigations have been launched at MAX IV Laboratory and Photon Science at DESY. Two permanently stationed t...

The structural and luminescence properties of undoped Y1−xScxPO4 solid solutions have been studied. An intense thermally stable emission with fast decay (τ1/e ~ 10−7 s) and a band position varying from 5.21 to 5.94 eV depending on the Sc/Y ratio is detected and ascribed to the 2p O-3d Sc self-trapped excitons. The quantum yield of the UV-C emission...

In recent years, demand for scintillation detectors with high time resolution (better than 100 ps) has emerged in high-energy physics and medical imaging applications. In particular, time of flight positron emission tomography (TOF-PET) can greatly benefit from increasing time resolution of scintillators, which leads to the increase of signal-to-no...

Na3.6Lu1.8-x(PO4)3:xEu3+ phosphors were synthesized by a high-temperature solid-state reaction. A powder X-ray diffraction study revealed that homogeneous solid solutions with a NASICON-type structure were formed at 0 ≤ x ≤ 0.7. The Na3.6Lu1.8(PO4)3 structure was refined from the powder X-ray diffraction data and the cation distribution in the latt...

Deep-UV (180-280 nm) phosphors have attracted tremendous interest in tri-band-based white light-emitting diode (LED) technology, bio- and photochemistry, as well as various medical fields. However, the application of many UV-emitting materials has been hindered due to their poor thermal or chemical stability, complex synthesis, and environmental ha...

Phase-pure crystalline micropowder samples of BaGeF6 were prepared and studied under excitation by tuneable synchrotron radiation and 10 keV electron beam. Time-resolved photoluminescence emission and excitation spectra and a set of single emission decay curves were recorded at 7 K for the exciting photon energy region of 4.3–45 eV. Several intrins...

Single-phase Na3.6Y1.8-x(PO4)3:xDy³⁺ phosphors were synthesized by high-temperature solid-state reaction. Powder X-ray diffraction study reveals that a homogeneous solid solution with a NASICON-type structure is formed at 0 ≤ x ≤ 0.4. Luminescence properties of the phosphors were studied using the methods of UV and VUV spectroscopy. Narrow emission...

Lithium molybdate single crystals up to one kilogram have been grown by a conventional Czochralski process. The growth configuration (geometry, coil, crucible, insulation casing) was optimized by numerical simulation of heat and mass transfer. Dislocations are shown to belong to the basal glide system. Their density (≤ 10⁴ cm⁻²) and luminescence pr...

In recent years, demand for scintillation detectors with high time resolution (better than 100 ps) has emerged in high-energy physics and medical imaging applications. In particular, time of flight positron emission tomography (TOF-PET) can greatly benefit from increasing time resolution of scintillators, which leads to the increase of signal-to-no...

Here, we present the results of the study of structure and luminescence properties of NASICON-type phosphors Na3.6A1.8(PO4)3 (A = Y, Lu) doped with RE ions (Eu3+, Dy3+).

Microsize powder of Mn-doped potassium hexaflourosilicate (PFS, K2SiF6) phosphor has been synthesized using the microwave-hydrothermal (MWHT) method, a new approach for obtaining this material. Special attention has been paid to the identification of the valence states for Mn doping ions using EPR and XANES techniques. Although photoluminescence re...

Highly crystalline K2GeF6 micropowders were prepared by co-precipitation in the hydrofluoric acid-water-alcohol solution and studied by means of the cathodoluminescence and time-resolved luminescence spectroscopy under synchrotron radiation excitation at 7 K. The nature of various intrinsic emissions was revealed. The luminescence band at 510 nm de...

The energy levels of Dy3+ ions have been determined in lithium yttrium borate (Li6Y(BO3)3) single crystals in a wide spectral range between 3000 and 40,000 cm−1 using optical absorption and luminescence spectroscopy, which also allow for an analysis of the ground state. The crystal field splittings of the 6H15/2 ground state and all excited states...

The origin and thermal stability of charge trapping centers were studied in Li2MoO4 cryogenic scintillators by correlated electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) measurements. Up to five electron and three hole trapping centers were detected in the crystals X-ray irradiated at 77 K. The electron traps were...

Cooperative luminescence (CL) of Yb³⁺ pairs was investigated in Yb-doped Li6Y(BO3)3 crystals. It was reliably distinguished from other types of up-conversion luminescence related to the energy transfer from Yb³⁺ ions to other rare-earth ions unintentionally introduced into the crystal. The CL was observed in the region of 19,000–21,000 cm⁻¹ (526-47...

CdWO4:Sm single crystals were studied by optical, electron-paramagnetic and thermoluminescence spectroscopy in the temperature range of 4–750 K. A hopping diffusion of self-trapped excitons and energy transfer to Sm³⁺ centres is demonstrated. The mechanism of energy transfer includes the formation of a Sm³⁺ bound exciton either by direct excitation...

The luminescence properties of ScxY1−xPO4:Eu3+ solid solutions have been studied under excitation by synchrotron radiation in the energy range of 4.5–50 eV. The luminescence originating from three different types of emission centers was observed, and the origin of the emission centers was determined. The light output of ScxY1−xPO4:Eu3+ was shown to...

We describe powders of SrSi2O2N2:Eu²⁺ green phosphor synthesized with various reactive agents in a wide range of concentration. Two approaches are described, the first is adding carbonate reactive agents (K2CO3 and Li2CO3) to the initial powders excessively and, the second, using SrF2 reactive agent as an additional Sr source to increase the reacti...

Large diameter Ti-doped sapphire single crystals grown by the Kyropoulos technique along the A-axis, show detrimental light scattering close to the central C-plane. Thermo-luminescence measurements evidence that this defect is associated to a high level of oxygen vacancies. X-ray topography and Rocking Curve Imaging were performed. They show that t...

The influence of Sc cation substituent on structural and luminescence properties of GAGG:Ce crystals was studied. Unit cell parameters and space group were obtained using the XRD analysis. The chemical compositions of the crystals were determined using SEM-EDX and TEM-EDX techniques. Structures were refined by Rietveld method and the distribution o...

Scintillators with ultrafast response are of demand in medical imaging for time-of-flight positron emission tomography, in high-energy physics calorimetry and other applications. There are several fast luminescence processes in solid-state materials, which could be good candidates for fast timing applications. The development of new ultrafast silic...

Charge carrier trapping was studied using EPR and TSL methods in ZnWO4, MgWO4 and mixed ZnxMg1-xWO4 crystals. An electron trapped at a perturbed W site was detected in MgWO4. It was also shown that holes are trapped at oxygen ions thus forming O−centers. Two different O− centers, one perturbed by a cation vacancy, another by Al impurity, were found...

Recent progress in various fields of scintillator applications has created a high demand for ultrafast timing. One of the perspective scintillation mechanisms for that is hot intraband luminescence (IBL). This is a universal intrinsic luminescence effect that occurs at the time scale of electron-phonon relaxation with characteristic time below 1 ps...

New features of isothermal build-up of thermally stimulated luminescence (TSL) related to deep traps in anion-deficient alumina single crystals are revealed. It was found that the TSL build-up at 630–750 K depends on the structure of the glow curve and is associated with the presence of a high-temperature component with Tm = 700 K. Isothermal TSL b...

For the first time we report the synthesis of nanocrystalline powders of Na3Al2Li3F12 phase, both pure and doped with Mn4+ using slow room temperature co-precipitation in methanol-water mixtures. Optical properties of obtained highly crystalline nanoparticles with the size in the range of 40-80 nm are studied. The synthesized Mn4+ doped fluoride ga...

FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5–1450 eV). A new mobile luminescence spectrosc...

The 14th International Conference on Inorganic Scintillators and Their Applications (SCINT 2017) was organized by CERN, and held on September 17–22, 2017, in Chamonix, France. This was a particular event in the series of SCINT conferences, since we celebrated the 25th anniversary of its birth in 1992. Intentionally, it has also been held at the pla...

The luminescence spectroscopy of various TbPO4, EuPO4 and TbPO4:Eu³⁺ polycrystalline materials has been systematically investigated upon near and vacuum UV excitation. Evidence was found for an efficient overall Tb³⁺→Eu³⁺ energy transfer in TbPO4:Eu³⁺. Upon UV excitation, this process leads to a significant change in the resulting emission colour o...

Cathodoluminescence yield of hot intraband luminescence (IBL) under ∼100 keV pulsed electron excitation was evaluated in several halide and oxide compounds. Its values lie in the range of 5–35 ph/MeV, which is in accordance with the general assumptions on the mechanism of IBL. The expected inverse correlation between the IBL yield and highest phono...

Single-phase ceramic samples of silicate apatites M2Ln8(SiO4)6O2 (M = Mg, Ca, Sr; Ln = Y, La) undoped and doped with Eu3+ , Ce3+ , or Mn2+ ions were obtained by the high-temperature solid-state reaction technique using precursors synthesized under hydrothermal conditions. The phosphors were characterized by XRD analysis, Raman spectroscopy, and ste...

Luminescent, optical and electronic properties of Na2Mo2O7 single crystals grown by two different procedures, the conventional Czochralski method and the low-temperature gradient Czochralski technique, are presented. The band structure calculations were performed in generalized gradient and local density approximations and allowed to determine the...

Manganese doped Li2B4O7 (LTB) crystals have been studied using luminescence and EPR spectroscopy, extending the investigations for the first time from the X band to the Q band for higher resolution. Mn²⁺ ions are shown to substitute dominantly at lithium sites charge compensated by a nearby lithium vacancy. Excitation spectra of the Mn²⁺ ion emissi...

Based on the results of spectroscopy studies and electronic band structure calculations, the analysis of excitation energy transformation into luminescence is performed for a set of molybdates MIIMoO4 (MII = Ca, Sr, Zn, Pb) and Li2MoO4. The bandgap energies were determined from comparison of experimental and calculated reflectivity spectra as 3.3 e...

Investigations of radioluminescence saturation in monocrystalline cerium doped yttrium aluminum garnet (Ce:YAG) exposed to intense extreme ultraviolet (XUV), soft X-ray and X-ray radiation delivered from three free-electron lasers are described in this article. The measurements were performed with wavelengths of 98, 25.6, 13.5 and 0.15 nm. We have...

Hot intraband luminescence (IBL) was observed under excitation by high-power (120keV, 10A/cm²) pulsed electron beam, low-energy (10keV) and low-current (2μA) continuous electron beam as well as pulsed x-rays. Thus, the fundamental possibility of IBL excitation by x-rays was confirmed, and for most studied materials the absence of the dependence of...

This work concerns the optical properties of alkaline earth yttrium apatites according to the composition AE2Y8Si6O26 (AE = Mg, Ca, Sr) doped with Eu³⁺, which are materials of interest for LED applications. Using a multistep preparation route, which includes hydrothermal synthesis of precursors for solid state reaction, ceramic samples were prepare...

Thermally stimulated luminescence (TSL) spectra in the 313–580 K temperature range have been studied in anion-defective alumina crystals (named in literature as Al2O3:C) exposed to different irradiation doses. The TSL curve features two peaks with the maxima at Tm1=437 K and Tm2=565 K. The TSL spectrum of the first peak contains the emission of F c...

Europium ions doped M2La8Si6O26 (M = Mg, Ca, Sr) silicate apatite phosphors have been synthesized by using solid-state reaction method, post-treated in a reducing atmosphere and studied by optical spectroscopy techniques. It has been revealed that the emission spectra from all the synthesized samples contain a set of spectral lines due to the 4 f –...

Research and development of new high-efficiency phosphors for white light generation using light emitting diodes (LEDs) is presently one of the most important topics for development of light sources for general and special lighting. LED light sources offer significant advantages compared to other lighting technologies: low power consumption, high e...

Nonlinear interaction of electronic excitations has been shown to play a remarkable role in luminescent material performance. Recently, it has been intensely studied in semiconductors and wide-gap scintillators. The nonlinear interaction is a cause of the nonproportionality of scintillator response to the energy of the absorbed ionizing radiation a...

Defects that are formed during crystal growth pose a serious obstacle for potential application of La3Ga5.5Ta0.5O14 (LGT) as a laser or piezoelectric crystal. We have performed the study of the defects origin in LGT crystals grown in different atmospheres using optical, EPR and time-resolved luminescence characterization methods. The absorption ban...

The creation spectrum of stable F centres (being part of F-H pairs of Frenkel defects) by synchrotron radiation of 7-40 eV has been measured for highly pure NaCl single crystals at 12 K using a highly sensitive luminescent method. It is shown that the efficiency of F centre creation in a closely packed NaCl is low at the decay of anion or cation ex...

The creation spectrum of stable F centres (being part of F–H pairs of Frenkel defects) by synchrotron radia-tion of 7−40 eV has been measured for highly pure NaCl single crystals at 12 K using a highly sensitive lumi-nescent method. It is shown that the efficiency of F centre creation in a closely packed NaCl is low at the decay of anion or cation...

Intraband luminescence (IBL) is a prompt emission originating from the radiative intraband transitions of charge carriers during thermalisation. Despite its low intensity, IBL can hopefully enhance scintillation time resolution, for instance, in positron emission tomography. The continuous and structureless spectrum of IBL spans over the whole tran...

The influence of growth conditions and doping with tungsten on the luminescent properties of ZnMoO4 is studied. An enhancement of luminescence intensity in crystals grown from the melt with Mo excess was detected and the origin of the effect is discussed. Time-resolved spectroscopy of ZnMoO4 allowed to separate two emission bands at 480 and 560 nm,...

The structural and luminescent properties of perspective scintillating ZnxMg1-xWO4 mixed crystals were studied. The following characteristics were found to depend linearly on x value: the energy of several vibrational modes detected by Raman spectroscopy, the bandgap width deduced from the shift of the excitation spectrum onset of a self-trapped ex...

The blue and green terbium luminescence excitation spectra (5–15 eV) at a temperature of 9 or 300 K have been measured for a set of CaSO4 : Tb3+ phosphors with calcium and terbium ions characterized by fundamental features, which were synthesized by the solid-state reaction method with variations in the composition of the raw material, the type of...

Homologue scheelite crystals CaWO4, SrWO4, and BaWO4 possess similar crystal and electronic structure, but their luminescence exhibits drastically different thermal stabilities. By measuring the temperature dependence of the decay time of the intrinsic luminescence and fitting it to a three level model, we have qualitatively shown the effective exc...

Solid phases of visible fluorescence substance (VFS) of biological fluids (blood, urine, hemodialysate) which was proposed earlier as a morbidity and mortality marker by renal failure and diabetes were investigated in-depth by the methods of electron and confocal microscopy, optical spectroscopy and matrix assisted laser desorption-ionization (MALD...

The structure of gadolinium oxyfluoride nanoparticles was revised. Extensive studies including X-ray diffraction and Rietveld refinement as well as Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the monoclinic P12/c1 crystal structure of Gd4O3F6. Morphological analysis using transmission electron microscopy showed the nano...

The international community of researchers on fundamentals, development, and applications of inorganic scintillator materials has found the biennial meetings of the SCINT series to be an excellent chance to exchange data and ideas. These can range from very basic physical concepts and atomistic mechanisms in the materials under study up to truly ap...

The combined luminescence and Raman-scattering microspectroscopy technique allows separate spectroscopic studies on several crystal phases in mixed compounds. A mixed sample of LiBaAlF6 and Ba3Al2F12 doped with Pr was studied. The Pr3+ concentration was found to be much higher in the Ba3Al2F12 phase. Several non-equivalent Pr3+ centers are present...

Non-irradiated and irradiated ceramics of Li2B4O7:Mn, Li2B4O7:Mn,Be, and Li2B4O7:Mn,Cu were studied using electron paramagnetic resonance and luminescence spectroscopy. The emission of Mn2+ centres is observed in the thermoluminescence spectra of the low-temperature and dosimetric high-temperature glow peaks in irradiated samples. Arguments are giv...

Time-resolved emission and excitation spectra as well as emission decay kinetics of CaF2, SrF2, BaF2 doped with HoF3 were investigated. Intensive emission bands near 168 nm, having long decay time, are caused by the spin-forbidden transitions from the 5d14f9 high-spin states to the ground 5I8 states of Ho3+ ions. Weak spin allowed 5d14f9(low-spin)-...

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO4:Tb3+ phosphors with different charge compensators (Na+, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (5D4 → 7FJ) and blue emission (5D3 → 7...

The decay kinetics of the excitonic emission of CdWO4 scintillators was studied under excitation by powerful 100 fs laser pulses in the band tail (Urbach) absorption region. A special imaging technique possessing both spatial and temporal resolution provided a unique insight into the Förster dipole-dipole interaction of self-trapped excitons, which...

Triclinic Gd1-xEuxBO3 nanophosphors have been prepared by a hydrothermal method without using additional coreagents and prior precipitation of precursor (in situ). The formation of the borate nanorods and their crystal structure was refined on the basis of X-ray diffraction patterns (XRD) and well confirmed using various techniques such as infrared...

The influence of some impurity ions on the increase/decrease in the resistance against irradiation of metal oxides with X-rays and electrons (low-dense excitation) or ∼2 GeV Au198 and U238 ions providing a superhigh density of electronic excitations along cylindrical tracks (LET > 30 keV nm−1) has been investigated for fcc MgO single crystals with...

Two technologically important tungstate crystals – CdWO4 and ZnWO4 – are studied theoretically using the plane wave based first-principles calculations. The optimized crystal structures were used to calculate the structural, electronic and elastic properties of both materials under varying hydrostatic pressure. It was shown that the band gaps, whic...