Correlational analysis of Eu3+ charge transfer state using La effective charge in La-based mixed-anion host compounds. (31st January 2017)

• Record Type: Journal Article
• Authors: Yoshimatsu, Ryo; Okada, Masahiro; Ishigaki, Tadashi; Watanabe, Shinta; Honma, Tetsuo; Ohmi, Koutoku
• Is Part Of: Japanese journal of applied physics. Volume 56:Number 3(2017)
• Publication Date: 2017-01-31
• Subjects: Physics -- Periodicals; 621.05
• DOI: 10.7567/JJAP.56.032601
• Languages: English
• ISSNs: 0021-4922

Abstract

Abstract: A prediction of the Eu 3+ charge transfer state ( E CT ) was attempted in La-based mixed-anion host compounds. We paid attention to La3 OF3 S2 :Eu, since it is expected to have a more covalent La site than La2 O2 S. The La effective charge (La EC) was proposed as the index factor of covalency and/or ionicity. The correlation between the experimental E CT and the calculated La EC was systematically analyzed for La2 S3, LaFS, La2 O2 S, La2 O3, LaOF, and LaF3 host materials, and good approximation was obtained using the single exponential function with a variable number of La ECs. According to the fitting curve, the E CT of La3 OF3 S2 :Eu was predicted to be 5.8 and 2.1 eV for Eu 3+ centers activated at ionic and covalent sites, respectively. To confirm the prediction accuracy, La3 OF3 S2 :Eu phosphor powder samples were synthesized by solid-state reaction. From the photoluminescence excitation and absorption measurements, the E CT values of about 4.7 eV (ionic La site) and 2.4 eV (covalent La site) were obtained. Even though the energy difference between the predicted and experimental values is large for the higher E CT, La EC is the useful index factor for estimating E CT . In addition, it indicates that the estimation can be applied to phosphor materials having multication sites.