Flux Crystal Growth, Crystal Structure, and Optical Properties of New Germanate Garnet Ce2CaMg2Ge3O12.

Jie Chen,Mark D Smith,Hans-Conrad Zur Loye,Yoshihiro Tsujimoto,Yoshitaka Matsushita,Yuki Iwasa,Akihide Kuwabara,Kazunari Yamaura,Hiraku Ogino,Hong Yan

doi:10.3389/fchem.2020.00091

Abstract

A new germanate garnet compound, Ce2CaMg2Ge3O12, was synthesized via flux crystal growth. Truncated spherical, reddish-orange single crystals with a typical size of 0.1–0.3 mm were grown out of a BaCl2-CaCl2 melt. The single crystals were characterized by single-crystal X-ray diffraction analysis, which revealed that it adopted a cubic garnet-type structure with a = 12.5487(3) Å in the space group Ia−3d. Its composition is best described as A3B2C3O12, where Ce/Ca, Mg, and Ge occupied the A, B, and C sites, respectively. A UV–vis absorption spectroscopy measurement on the germanate garnet revealed a clear absorption edge corresponding to a band gap of 2.21 eV (λ = 561 nm). First-principle calculations indicated that the valence band maximum was composed of Ce 4f bands, whereas the conduction band minimum mainly consisted of Ce 5d bands. These findings explain the observed absorption edge through the Ce 4f → 5d absorption. Photoluminescence emission spectra exhibited a very broad peak centered at 600 nm, corresponding to transition from the lowest energy d level to the 4f levels.

Highlights

The garnet structure, having the general chemical formula {A}3[B]2(C)3O12, has been widely studied as a host material for various optical applications, such as laser amplifiers, color converters, scintillators, and cathode ray phosphors (Zhiguo and Meijerink, 2017)
Owing to the wide range of cations that can be accommodated by the garnet structure, new compositions of garnet phosphors that compensate for the above-mentioned shortcomings of Y3Al5O12 garnet phosphor (YAG):Ce have been successfully synthesized
Single crystals of Ce2CaMg2Ge3O12 were crushed with an agate mortar and pestle to obtain fine powders used for obtaining synchrotron X-ray powder diffraction (SXRD) patterns, UV– vis diffuse reflectance spectra, and photoluminescence (PL) and photoluminescence excitation (PLE) spectra

Summary

INTRODUCTION

The garnet structure, having the general chemical formula {A}3[B]2(C)3O12, has been widely studied as a host material for various optical applications, such as laser amplifiers, color converters, scintillators, and cathode ray phosphors (Zhiguo and Meijerink, 2017). The structure of Ce2CaMg2Ge3O12 was determined by single-crystal X-ray diffraction analysis. Single crystals of Ce2CaMg2Ge3O12 were crushed with an agate mortar and pestle to obtain fine powders used for obtaining synchrotron X-ray powder diffraction (SXRD) patterns, UV– vis diffuse reflectance spectra, and photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The products obtained via solid state reactions were examined at room temperature by powder XRD analysis using a Rigaku MiniFlex X-ray diffractometer (Cu Kα radiation) in the 2θ range of 5–65◦ with a step size of 0.04◦. Structure optimization calculations were carried out until the residual forces were

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT