Luminescence of europium and ytterbium ions in strontium hexaborate

Abstract

We have studied the luminescent properties of Eu 2+/3+ and Yb 2+ ions in strontium hexaborate SrB 6 O 10 for excitation in the 120-400 nm region. The luminescence spectra of Ln 2+ ions in SrB 6 O 10 consist of overlapping bands in the 370-520 nm region, due to 5d → 4f transitions at several nonequivalent centers. In the excitation spectra, besides the bands associated with 4f → 5d transitions in the Ln 2+ ions, we also observe a band in the 135-160 nm region due to the transitions O(2p) → B(2s,2p) within the borate anions. The luminescence of the Eu 3+ ions is excited most efficiently in the region of the Eu 3+ charge transfer band (λ max = 226 nm). The results obtained are compared with data for Ln in other strontium borates.Introduction. Alkaline earth borates and solid solutions based on them are widely used as nonlinear optical crystals for obtaining coherent radiation in the UV region of the spectrum [1, 2], and also as luminophores for various purposes [3,4]. This is why a detailed study of their optical and luminescent properties is needed. Luminescence of lanthanide (Ln) ions (Ce 3+ , Sm 3+ , Eu 2+ , Tb 3+ ) in strontium hexaborate SrB 6 O 10 when excited in the 240-400 nm region has been studied in [5][6][7][8][9]. We know [6] that two types of Ce 3+ centers are present in solid solutions of composition Sr 1-x Ce x B 6 O 10 (x ≤ 0.01) obtained in an inert medium (N 2 ). One type of center is formed by direct substitution of strontium ions Sr 2+ with no local charge compensation, while the second type of center is an associate of a Ce 3+ cerium ion and a cationic (Sr) vacancy. The crystal structure of SrB 6 O 10 has not been deciphered in detail, but luminescence and EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy have established the presence in the structure of an Sr position characterized by a high coordination number (N = 9), a comparatively long Sr-O distance (R Sr-O ≥ 2.7 Å), and low point symmetry [6,7]. Efficient Ce 3+ → Tb 3+ energy transfer has been observed in strontium hexaborate, which allowed the authors of [8] to recommend a composition with formula Sr 0.68 Ce 0.08 Tb 0.08 Na 0.16 B 6 O 10 for use in lighting devices as a photoluminophore. The luminescence spectrum of Eu 2+ ions in SrB 6 O 10 for UV excitation consists of three bands with maxima at 390 nm, 435 nm, and 470 nm, which are assigned to 4f 6 5d → 4f 7 transitions in Eu 2+ ions occupying three nonequivalent positions [9]. The excitation and luminescence spectra of Eu 3+ ions in SrB 6 O 10 at 293 K are shown in [10], but the nature of the impurity luminescence centers was not analyzed because fine structure did not appear in the spectra at room temperature.In this paper, we present the results of a more detailed study of the luminescent properties of Eu 2+ /Eu 3+ ions in SrB 6 O 10 for optical and synchrotron excitation in the 120-340 nm region. Note that the results obtained for Eu 3+ ions are considerably different from the data in [10]. Data on the luminescent properties of Yb 2+ ions in SrB 6 O 10 are presented he...

Facile route for synthesis of strontium hexaborate crystalline powders

“…It is the first time that the bandgap of SrB 6 O 10 nanostructure is reported. The value of calculated bandgap is lower than reported values by others 29,30 . The difference among these values maybe is due to the particle size and morphology.…”

“…The value of calculated bandgap is lower than reported values by others. 29,30 The difference among these values maybe is due to the particle size and morphology. It is one of the important aspects of this study in which a method for the preparation of strontium hexaborate compound with its potential high-tech applications is developed.…”