Dmitriy Sofich

The development of efficient scintillators emitting in the red and/or infrared spectral range represents an important scientific challenge, as such materials could find numerous practical applications. This work studies newly grown CsI:Yb,Sm and CsI:Eu,Sm single crystals demonstrating red and infrared luminescence. We measured luminescence spectra in the visible and near-IR range, excitation spectra across visible, UV, VUV, and X-ray ranges, Raman spectra, and thermoluminescence spectra. The results show that divalent europium and ytterbium ions can efficiently transfer excitation to samarium ions. The light output of the obtained crystals under X-ray excitation was roughly estimated from the X-ray luminescence spectra, with expected values of 37,000 photons/MeV for CsI:Yb,Sm and 40,000 photons/MeV for CsI:Eu,Sm.

The development of efficient scintillators emitting in the red and/or infrared spectral range represents an important scientific challenge, as such materials could find numerous practical applications. This work studies newly grown CsI:Yb,Sm and CsI:Eu,Sm single crystals demonstrating red and infrared luminescence. We measured luminescence spectra in the visible and near-IR range, excitation spectra across visible, UV, VUV, and X-ray ranges, Raman absorption spectra, and thermoluminescence spectra. The results show that divalent europium and ytterbium ions can efficiently transfer excitation to samarium ions. The measured X-ray light yield reached 37,000 photons/MeV for CsI:Yb,Sm and 40,000 photons/MeV for CsI:Eu,Sm.

The single crystals of CsI-Yb²⁺ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb²⁺ is due to 5d–4f transitions in Yb²⁺ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb²⁺ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb²⁺ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb²⁺ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb²⁺ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors.

Solving the problem of searching for new scintillators based on available materials, we were the first to obtain and study a single crystal of CsI doped with divalent ytterbium ions. This work was directed to study of luminescence mechanism of Yb2+ ions and excitation transfer from crystalline matrix of CsI to dopant ions under VUV excitation. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were discovered. At 10 degrees, the emission of self-trapped excitons was detected. UV and VUV excitation spectra were obtained in the emission bands of ytterbium and self-trapped excitons. It was found that Yb2+ luminescence is excited in the excitonic region in the range of 10-45 eV. The mechanism of charge compensation of Yb2+ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity-vacancy complexes in two different positions.It is concluded that Yb2+ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors.

A series of novel KSrY_1–x Er _x (BO₃)₂ (x = 0–1) phosphors that emit near-infrared radiation was synthesized using solid-state methods. Pure Y and Er crystals were grown using a KF flux via the top-seeded solution growth technique. In situ high-temperature single crystal X-ray diffraction, Raman spectroscopy and DFT calculations were used for characterization. Within the series, a polymorphic phase transition from space group P2₁/m to R 3 m was discovered between 550 and 600°C. The concentration dependence of the luminescence intensity was measured for the samples. A strong emission of Er³⁺ electron transition ⁴I_13/2 → ⁴I_15/2 was detected within the 1529–1549 nm range, with the maximum observed for the KSrY_0.4Er_0.6(BO₃)₂ composition.

The article describes the process and parameters of growing CsI:Sm2+ single crystals by the Czochralski method. Spectroscopic studies of the CsI:Sm2+ single crystal have been carried out; it has been established that samarium ions enter the caesium iodide single crystal in the divalent state. At room temperature, luminescence is observed corresponding to the 4f55d1-4f6 transitions of divalent samarium; on cooling, only radiative 4f6-4f6 transitions are observed. The temperature dependence of the luminescence has been measured, the barrier energy has been determined, and the decay times of the luminescence have been measured.

New polycrystalline powder samples of double Ln2Zr(WO4)5 (Ln = Dy, Tb) tungstates were synthesized using high-temperature solid-phase and sol-gel methods. The conditions of the sol-gel synthesis of tungstates were optimized. The obtained phases were characterized by the X-ray powder diffraction on the basis of the crystallographic data of similar Ln–Zr molybdates. It is found that Ln2Zr(WO4)5 (Ln = Dy, Tb) double tungstates crystallize in the orthorhombic crystal system, space group Cmc21 (Z = 4). The intensive luminescence in the green spectral region for Tb2Zr(WO4)5 and yellow spectral region for Dy2Zr(WO4)5 was shown.

The optical spectra of BaBrI crystals activated by divalent samarium were studied. The samples exhibit bright luminescence in the red region of spectra due to 4f⁶–4f⁶ and 4f⁵5d¹–4f⁶ transitions of Sm²⁺ ions. Luminescence exhibits strong temperature dependence in the range 7–300 K. At low temperatures, luminescence associated with parity-forbidden 4f⁶–4⁶f transitions from ⁵D₀ and ⁵D₁ states is observed. Coloring of the crystals after irradiation by ultraviolet light and long afterglow luminescence of BaBrI:Sm²⁺ were detected.

К настоящему времени всесторонне изучены двойные молибдаты одно- и четырёхвалентных элементов, достаточно полно исследованы системы с молибдатами одно- и трёхвалентных элементов. Некоторые материалы на основе двойных молибдатов, например, содержащие лантаниды, являются перспективными для лазерной техники и электроники. Между тем, сведения о свойствах, особенно оптических, у молибдатов, содержащих редкоземельные элементы и цирконий, ограничены. Целью данной работы являлось исследование люминесцентных свойств самоактивированных тербийсодержащих циркономолибдатов составов Tb2Zr3(MoO4)9 (1:3) и Tb2Zr(MoO4)5 (1:1),кристаллизующихся в двух разных структурных типах.Порошковые образцы исследуемых молибдатов синтезированы керамической технологией. В работе использованы методы измерения спектров поглощения, возбуждения и люминесценции с помощью спектрофотометра Perkin Elmer Lambda 950. Люминесценция возбуждалась ксеноновой лампой ДКСШ-250 мощностью 250 Вт через монохроматор МДР-2 и регистрировалась с помощью двойного монохроматора СДЛ-1 с решеткой 600 штрихов/мм. В работе исследованы оптические свойства новых циркономолибдатов, содержащих ионы Tb3+. В них обнаружена яркая люминесценция в зелёной области спектра, обусловленная переходами внутри 4f- оболочки редкоземельного иона Tb3+, возбуждающегося как в полосах, связанных с 4f–4f переходами, так и в полосе с переносом заряда.Идентифицированы наблюдаемые спектральные линии и полосы люминесценции и возбуждения.Показано, что положение широкой полосы возбуждения, связанное с переходами «с переносом заряда» от O2– в группах MoO4 2– через связи Mo–O к люминесцентным центрам (Tb3+), не зависит от структуры матрицы. Структура и интенсивность наблюдаемых спектральных линий, свидетельствующие о низкой симметрии кристаллического окружения Tb3+, коррелируют с данными структурного анализа. Полученные в работе результаты могут быть использованы при создании перспективных люминофоров в зеленой области спектра при ультрафиолетовомвозбуждении. ЛИТЕРАТУРА 1. Софич Д. О., Доржиева С. Г., Чимитова О. Д., Базаров Б. Г., Тушинова Ю. Л., Базарова Ж. Г., Шендрик Р. Ю. Гиперчувствительный переход 5D0−7F2 трехвалентного европия в двойных молибдатах.Изв. РАН, Сер. физич. 2019;83(3): 384–387. DOI: https://doi.org/10.1134/S03676765190302202. Sofi ch D., Tushinova Yu. L., Shendrik R., Bazarov B. G., Dorzhieva S. G., Chimitova O. D., BazarovaJ. G. Optical spectroscopy of molybdates with composition Ln2Zr3(MoO4)9 (Ln: Eu, Tb). Opt. Mater. 2018;81:71–77. DOI: https://doi.org/10.1016/j.optmat.2018.05.0283. Софич Д., Доржиева С. Г., Чимитова О. Д., Базаров Б. Г., Ю.Л. Тушинова Ю. Л., Базарова Ж. Г.,Шендрик Р. Ю. Люминесценция ионов Pr3+ и Nd3+ в двойных молибдатах. ФТТ. 2019;61(5): 943–945.DOI: https://doi.org/10.21883/FTT.2019.05.47598.35F4. Доржиева С. Г., Тушинова Ю. Л., Базаров Б. Г., Непомнящих А. И., Шендрик Р. Ю, Базарова Ж. Г.Люминесценция Ln-Zr-содержащих молибдатов. Изв. РАН. Сер. физич. 2015;79(2): 300–303.DOI: https://doi.org/10.7868/S03676765150200765. Baur F., Justel Th. New red-emitting phosphor La2Zr3(MoO4)9:Eu3+ and the infl uence of host absorptionon its luminescence effi ciency. Aust. J. Chem. 2015;68(11): 1727–1734. DOI: https://doi.org/10.1071/CH152686. Qi S., Huang Y., Cheng H., Seo H. J. Luminescence and application of red-emitting phosphors of Eu3+-activated R2Zr3(MoO4)9 (R = La, Sm, Gd). Electron. Mater. Lett. 2016;12(1): 171–177. DOI: https://doi.org/10.1007/s13391-015-5244-17. Базарова Ж. Г., Тушинова Ю. Л., Базаров Б. Г., Доржиева С. Г. Двойные молибдаты редкоземель-ных элементов и циркония. Изв. АН. Сер. химич. 2017;(4): 587–592. Режим доступа: https://elibrary.ru/item.asp?id=291126318. Клевцова Р. Ф., Солодовников С. Ф., Тушинова Ю. Л., Базаров Б. Г., Глинская Л. А., Базарова Ж. Г.Новый...

The optical spectra of samples of double zirconium molybdates activated by rare-earth Pr3+ and Nd3+ ions are studied. The presence of bands corresponding to the 4 f–4 f transitions of Pr3+...