Samples of Gd2O3:Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800oC and 1200oC in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, radiation spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb4+ and Tb3+ respectively. The diffuse reflection spectra of the sample after annealing at 800oC under optical excitation showed a direct charge transition through the bandgap with Eg = 2.56 eV. After elevated annealing temperature the concentration of Tb4+ ions decreases due to reduction to Tb3+. As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with Eg = 2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with Eg = 3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm.
Люминофоры Gd2O2S : Tb(3-7 mol.%), полученные через стадию золь-гель формирования прекурсоров Gd2O3 : Tb с последующим их сульфидированием в парах серы с плавнем LiF при 700oC, показали высокую эффективность свечения. Характеризацией полученных образцов набором физико-химических методов установлено, что увеличение концентрации активатора Tb3+ приводит к его специфическому распределению: по вакансиям гадолиния (VGd)''', замещением ионов Gd3+ и концентрированием его на границах кристаллитов. Отмечено, что при этом изменяется морфология кристаллитов, изменяется ближний порядок структурной единицы решетки (Gd2O2) c внедрением ионов S2- в вакансии кислорода [VO]oo или замещением анионов O2-, в результате чего нарушается дальний порядок анионной подрешетки и уменьшается ширина запрещенной зоны. При этом, образующиеся примесные фазы GdOF : Tb и TbOF способствуют повышению эффективности фотолюминесценции. Вариации этих эффектов при росте концентрации Tb3+ приводят к росту интенсивности полос излучения зеленой области переходов 5D4->7Fj и снижению интенсивности полос излучения синей области переходов 5D3->7Fj. Ключевые слова: люминофор Gd2O2S : Tb(3-7 mol.%), реальная структура решетки, распределение активатора фотолюминесценции, дальняя инфракрасная спектроскопия, рамановская спектроскопия, РФЭС-спектроскопия.
In this work, we investigated the features of the photoluminescence of C-Gd2(1-x)TbxEuxO3 luminophores at x = 1.0 and 2.5 mol%, which are associated with the distribution of Tb3+ and Eu3+ activator ions over the centrosymmetric C3i and noncentrosymmetric C2 positions of cations in the bixbyite lattice, as well as in the positions at the boundaries crystallites CS. We studied the phase transformations of the samples, changes in the morphology of crystallites, photoluminescence spectra, and spectra of the far infrared region 50–600 cm–1 with changes in the annealing modes of the initial products of the sol – gel synthesis Gd2(1 – x)TbxEux(OH)y(CO3)z · n(H2O) at temperatures of 900 and 1200oC in air and hydrogen. Correlations have been established between changes in the characteristics of the samples and the parameters of their annealing. Based on the analysis of these correlations, the redistribution of activators over the indicated cation positions was determined, and a model was proposed for identifying infrared absorption bands in accordance with the localization of activators along the cationic sublattices C3i and C2.
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