Elsevier

Journal of Luminescence

Volume 128, Issue 7, July 2008, Pages 1108-1112
Journal of Luminescence

Optical properties and local structure of Eu3+-doped synthetic analogue of the microporous titanosilicate mineral sitinakite

https://doi.org/10.1016/j.jlumin.2007.11.085Get rights and content

Abstract

The synthetic analogue of the microporous titanosilicate mineral sitinakite has been hydrothermally synthesized and used as a host in the preparation of a new photoluminescent material. The inclusion of Eu3+ in the pores of the sitinakite doubles the unit cell volume and changes the symmetry of the initial sodium phase. The Eu3+-doped material displays a stable room temperature emission ascribed to the Eu3+ intra-4f6 5D07F0−4 transitions, with a maximum external quantum yield of 6%. The observation of two components for the non-degenerated 5D07F0 transition, the local field splitting of the 5D07F1−2 transitions, and the 5D0 emission decay curves point out the presence of two optically active Eu3+ sites. Possible structural distribution of the detected Eu3+ cations is discussed.

Introduction

The recent history of the family of the microporous titanosilicates is dominated by investigations of their classical zeolitic properties of catalysis, ion exchange, adsorption and separation. However, not long time ago a new possible application of these materials as a host for optically active environments has been proposed [1]. Here we turn our attention to the microporous titanosilicate analogue of the mineral sitinakite [2], [3]. Recently, the synthetic sitinakite (Na2Ti2O3SiO4·2H2O) has attracted considerable interest due to its selective ion exchange properties, which makes it a promising material for remediation of ground water and certain type of nuclear wastes [4], [5]. The structure of sitinakite has a one-dimensional channel system composed of TiO6 octahedra occurring in clusters of four sharing edges to form a cube-like unit. The clusters are connected along c-axis by Ti–O–Ti bonds, and along a- and b-axis by SiO4 tetrahedra whose oxygen atoms form part of the cluster. There are two crystallographic positions for eight Na+ ions in the unit cell. One sodium site is within the framework bonded to four oxygen atoms of silicate and two water molecules. The other site is in the tunnels with pore openings approximately 3.5 Å wide [3].

In this report, we extend the classical zeolitic properties of sitinakite and use its open framework as host to embedding Eu3+, which results in the creation of a new optical material. The properties and local distribution of the Eu3+ local coordination sites within the framework and in the channels are studied on the basis of photoluminescence spectroscopic data. In this paper, we also report, for the first time, absolute emission quantum yields on microporous titanosilicates, enabling the quantification of the photoluminescence features of such materials class.

Section snippets

Experimental

The synthetic sitinakite was prepared using the following molar composition: 1.6Na2O:SiO2:0.78TiO2:20H2O. Typically, sodium silicate solution (27 wt% SiO2, 8 wt% Na2O, Merck), water, NaOH and anatase were mixed and heated in a Teflon-lined autoclave at 170 °C for 6–7 days. Autoclave was removed and quenched in cold water. The resulting crystals were filtered and washed at room temperature with distilled water, and dried at 90–100 °C.

Eu3+-doped sitinakite powder was prepared via ion exchange as

Results and discussion

Fig. 1 shows direct comparison between powder XRD patterns of the as-synthesized and Eu3+-doped sitinakite. The phase retains its structural integrity although the inclusion of Eu3+ has resulted in vastly decreased crystallinity. Using the FullProf program [6] the unit cell parameters of the as-synthesized sodium sitinakite were refined (P42/mcm, a=b=7.806(3)Å, c=11.959(1) Å, V=728.76 Å3), and are in a fair agreement with the previously reported ones (P42/mcm, a=b=7.8082(2)Å, c=11.9735(4) Å, V

Conclusion

In summary, a synthetic analogue of the mineral sitinakite is synthesized and doped with Eu3+. The inclusion of Eu3+ in the pore system causes structural changes detected by powder XRD and studied by the photoluminescence spectroscopy. It is estimated that Eu3+-doped sitinakite has doubled unit cell volume and higher symmetry when compared with the initial sodium phase. Photoluminescence study indicates the presence of two active local europium sites, which supports the powder XRD

Acknowledgments

The authors thank the financial support from FCT, POCI2010 and FEDER. S. Ferdov also thanks FCT (SFRH/BPD/23771/2005) for the grant.

References (14)

  • Z. Lin et al.

    Microporous Mesoporous Mater.

    (2005)
  • A. Tripathi et al.

    J. Solid State Chem.

    (2005)
  • R.G. Anthony et al.

    Waste Manage.

    (1993)
  • A. Tripathi et al.

    J. Solid State Chem.

    (2003)
  • G. Blasse et al.

    J. Inorg. Nucl. Chem.

    (1967)
  • G.F. de Sá et al.

    Coord. Chem. Rev.

    (2000)
  • E.V. Sokolova et al.

    Dokl. Akad. Nauk SSSR

    (1989)
There are more references available in the full text version of this article.

Cited by (7)

  • Temperature and time controlled crystallization in Na<inf>2</inf>O–SiO<inf>2</inf>–TiO<inf>2</inf>–H<inf>2</inf>O system

    2022, Microporous and Mesoporous Materials
    Citation Excerpt :

    In 2007, Kostov-Kytin et al. reported a systematic study on the synthesis of titanosilicates and reduced the time for crystallization of CST to only 24 h by using TiCl4, SiO2 (200 μm particle size) and NaOH [17]. Ferdov et al. obtained synthetic sitinakite using TiO2 (anatase), Na2SiO3, and NaOH at 170 °C for 144–168 h in 2008 [9] and GTS-1 at 90 °C for 18 h using TiCl4 in 2004 [18]. Kalashnikova et al. showed crystallization fields of different titanosilicates where our estimate indicates that the synthetic analogue of the mineral sitinakite might have been obtained for 4 h. However, powder XRD patterns and discussion about the exact duration of the synthesis have not been presented [19].

  • Photoluminescent porous and layered lanthanide silicates: A review

    2016, Microporous and Mesoporous Materials
    Citation Excerpt :

    In 2009, Yakovenchuk et al. [80] reported the existence of the mineral ivanyukite, a titanosilicate of the pharmacosiderite type whose distinct nomenclature was given due to observable differences on the symmetry of the crystal structure caused by the existence of an extraframework cation [80,81]. Concerning the doping of both materials with Eu3+, Ferdov et al. [33,34] did not follow the common procedure described previously for ETS-10 and synthetic umbite because the calcination was not necessary. Hence, after the synthesis, sitinakite and ivanyukite were doped with the lanthanide by means of a conventional ion exchange, creating new optical materials that display a stable room temperature emission in the red spectral region.

  • Thermal flexibility of microporous titanosilicate with distorted pharmacosiderite structure

    2012, Microporous and Mesoporous Materials
    Citation Excerpt :

    Together with ETS-4 there are known ten synthetic hydrated open framework titanosilicates [12], whose thermal behavior and applied properties are extensively studied. Among them the microporous titanosilicates with pharmacosiderite (GTS-1) [13–15] and sitinakite (TAM-5) [16–18] structures have attracted an interest due to thir specific zeolitic properties and the possibility for optical activation by doping with rare-earth elements [19,20]. These porous solids allow selective uptake of Sr2+ and Cs+ in the presence of ppm levels of Ca2+, Mg2+, K+ and Na+ in slightly acid to neutral solutions [16–18,21–22].

View all citing articles on Scopus
1

On leave from the Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences.

View full text