Photon Factory Activity Report 2019 #37 (2020)

BL-5A/2018G551

Identification and structures of the X-ray induced luminescence centers in the zeolites
Zr,X,Cs,Na-LTA, X = Cl, Br, and I
Hyeon Seung Lim1, Joon Young Kim1, Gi Beom Park1, Jae Gwon Jeong 1, Nam Ho Heo1,*,and Karl Seff2
1
Department of Applied Chemistry, School of Applied Chemical Engineering, Kyungpook National
University, Daegu, 41566, Korea
2
Department of Chemistry, University of Hawaii, 2545 The Mall, Honolulu, Hawaii, 96822, U. S.
1 Introduction
X-ray induced luminescence (XIL) has been extensively
utilized in medical imaging, physics, homeland security,and related industries.1 In applications it is critical that theXIL wavelengths be well matched with optical sensors
such as photomultiplier (PMT) and silicon photomultiplier(SiPM) tubes for the efficient conversion of light toelectronic signals. However, unless the luminescentmaterials are doped with rare earth elements, thisoptimization is methodologically limited.
Recently, Sun et al. reported that color-tunable CsPbX3zeolite Y (X = Cl, Br, and I), where “quantum dots ofperovskite” are encapsulated in the pores of the zeolite,luminesced upon ultraviolet (UV) irradiation. They foundthat the emission spectra of that zeolite could be tuned
throughout the visible spectral range by varying its halide
anion composition.2
In this work, we report the preparation, structures, andluminescent properties of three Cs,Na-A zeolites
containing Zr4+ and different halide anions, Zr,X,Cs,Na-A
where X = Cl, Br, and I.
2 ExperimentSingle crystals of Zr,Cl,Cs,Na-A,3 Zr,Br,Cs,Na-A, andZr,I,Cs,Na-A were prepared from Cs,Na-A (Cs7Na5-LTA)
as follows. Fully dehydrated single crystals of Cs,Na-A
were exposed to ZrCl4(g), ZrBr4(g), and ZrI4(g) at 523 K,
543 K, and 573 K, respectively, for 48 h. Their crystal
structures
weredeterminedbysingle-crystal
crystallography using synchrotron X-radiation and theircompositions were confirmed by SEM-EDX analyses.
Their structures were refined in the space group Pm 3 m (a= 12.230(1), 12.235(2), and 12.210(2) Å), with all uniquedata to the final error indices R1 = 0.069, 0.051, and 0.072,
respectively. XIL images (CCD) of the three crystals wereobtained using synchrotron X-radiation (Figure 1a).
The X-ray induced luminescence spectra of similarly
prepared anhydrous powder samples were recorded at 293
K with a Flame-T spectrometer (Ocean optics, 50 kV, 30mA). The scintillation decay times were measured bydirectly coupling the vessel containing each powder to theentrance window of the photomultiplier tube (PMT,H6610). Each sample was excited with a XR200 pulsed
X-ray beam.

Fig 1. CCD images of anhydrous Zr,X,Cs,Na-A single
crystals luminescing upon synchrotron X-irradiation at 298
K (Photon Factory, Tsukuba, Japan, 16.5 keV, 450 mA):
Zr,Cl,Cs,Na-A (blue), Zr,Br,Cs,Na-A (green), andZr,I,Cs,Na-A (red). (b) X-ray induced luminescence
spectra of anhydrous Zr,Cl,Cs,Na-A, Zr,Br,Cs,Na-A, andZr,I,Cs,Na-A powder samples.
3 Results and Discussion
The XIL domain peaks have red-shifted from 495 nm for
Zr,Cl,Cs,Na-A, to 520 nm for Zr,Br,Cs,Na-A, and to 640
nm for Zr,I,Cs,Na-A (Figure 1b). This may be because theself-trapped excitons (STE) of ZrBr62- and ZrI62- havesmaller band gaps than that of ZrCl62-, a result of thevalence band maximum 4p energy level in Br- being higher(5p in I- even higher) than the 3p energy level in Cl-. In thethree structures, most Na+ and Cs+ ions occupy positions
similar to those in Cs,Na-A. About 14%, 9%, and 6% of
the large cavities of Zr,Cl,Cs,Na-A, Zr,Br,Cs,Na-A, andZr,I,Cs,Na-A are centered by ZrCl62-, ZrBr62-, and ZrI62ions, respectively. These octahedral ZrX62- ions are each
held in place and stabilized at the centers of their large
cavities by 24 bonds between all six of its halide ions anda cube of eight surrounding Cs+ ions. They are further
bridged by 8-ring Cs+ ions to form a 3-dimensional
Cs11ZrX69+ continuum in the surface volume of the crystal(Figure 2).

Fig 2. Complexes and clusters in Zr,X,Cs,Na-A: (a) ZrX62-,(b) each ZrX62- ion associates further with a cube of eightsurrounding Cs+ ions (Cs4), (c) six bridging Cs+ ionsassociate with each Cs8ZrX66+ group to give Cs14ZrX612+,and (d) eight ZrX62- ions (alternatively Cs8ZrX66+ groups)
are bridged by 12 Cs+ ions to show a portion of the cationic
Cs11ZrX69+ continuum.

Photon Factory Activity Report 2019 #37 (2020)

Acknowledgement
We gratefully acknowledge the Photon Factory, HighEnergy Accelerator Research Organization, KEK,
Tsukuba, Japan for the use of their synchrotron facilities
including diffractometer and computing systems.
References[1] S. Derenzo, M. Weber, E. Bourret-Courchesne, M.
Klintenberg, Nucl. Instr. and Meth. A 505, 111 (2003).
[2] J.Y. Sun, F.T. Rabouw, X.F. Yang, X.Y. Huang, X.P.
Jing, S. Ye, Q.Y. Zhang, Adv. Funct. Mater. 27, 1704371(2017).
[3] C.W. Lee, J.Y. Kim, H.J. Kim, N.H. Heo, K. Seff, J.
Phys. Chem. C 120, 18682 (2016).
* nhheo@knu.ac.kr