Synthesis and photoluminescence properties of perovskite KMgF 3 :Eu nanocubes
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KMgF3:Eu nanocubes with a mean edge length of ;12 nm were synthesized by a hydrothermal method. Result of x-ray diffraction reveals that the nanocubes are perovskite phase. Under ultraviolet excitation, the broad emission bands from trace oxygen and color centers in KMgF3 matrix were observed. In comparison with a bulk sample having the same chemical compositions, no characteristic emissions of Eu21 were observed, which can be attributed to the overlappment of the emissions of Eu21 and color centers in KMgF3:Eu nanocubes. In addition, the emissions of Eu31 were also detected, and the intensity ratio of 5D0 / 7F2 to 5D0 / 7F1 changed with excitation wavelength, indicating that the material has multiple luminescence centers or emitting states. I. INTRODUCTION
II. EXPERIMENTAL
Fluorides doped with rare-earth (RE) ions have garnered extensive research attention due to their potential applications in optical telecommunication, lasers, optoelectronic devices, diagnostics, and biological labels.1–12 In comparison with oxygen-based systems, fluorides have an advantage as a fluorescent host matrix owing to their low phonon energies and the resulting minimization of the quenching of the excited state of the RE ions.13,14 In particular, KMgF3 was an ideal host lattice for RE ions because not only KMgF3 has good homogeneous optics, high thermal stability, low melting point, anisotropy, and high optical transparency, but also KMgF3 could stabilize low-valence RE ions, which could be used to further refine spectral structure of these RE ions. For example, Eu21 ion in KMgF3 single crystals can substitute K1 ion and exhibits an intense blue fluorescence, which is assigned to the d–f transition within Eu21 electronic configuration.15,16 Pure and doped KMgF3 single crystals have been studied extensively by Shi et al.17–19 Recently, a great deal of research effort has been devoted to the synthesis of RE-doped nanocrystals.20–24 Nanosized phosphors or optoelectronic devices usually exhibit novel capabilities, such as high efficiencies, tunable wavelengths, and rapid responsibilities,25–31 resulting from the quantum effects and a high surface-to-volume ratio compared to their bulk counterparts. Herein, we successfully prepared perovskite KMgF3:Eu nanocubes with a mean edge length of ;12 nm according to our reported liquid–solid–solution (LSS) strategy.12,32 The photoluminescence properties were studied in detail.
In a typical synthesis, 4 mL of KF aqueous solution (0.5 mol/L) and 1 mL of chlorate (MgCl2 and EuCl3) aqueous solution (0.5 mol/L) were added to a mixture of NaOH (1.2 g), ethanol (8 mL), deionized water (4 mL), and oleic acid (20 mL), and the solution was thoroughly stirred. Subsequently, the milky colloidal solution was transferred to a 50 mL Teflon-lined autoclave and heated at 160 °C for 24 h. The systems were then allowed to cool to room temperature. The final products were collected by means of centrifugation, washed with ethanol, and finally dried in vacuum at 80 °C for 4 h. For comparison, the corresponding bulk sample with
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