Polymorphism and photoluminescence properties of K3ErSi2O7. Issue 10 (25th September 2019)

• Record Type: Journal Article
• Authors: Dabić, Predrag; Nikolić, Marko G.; Kovač, Sabina; Kremenović, Aleksandar
• Is Part Of: Acta crystallographica. Volume 75:Issue 10(2019)
• Page Start: 1417
• Page End: 1423
• Publication Date: 2019-09-25
• Subjects: alkali rare‐earth silicates -- lanthanide silicates -- polymorphism -- photoluminescence -- crystal structure; Crystallography -- Periodicals; Crystals -- Periodicals; 548.3
• DOI: 10.1107/S2053229619011926
• Languages: English
• ISSNs: 2053-2296

Abstract

Abstract : The crystal structures of two tripotassium erbium disilicate, K3 ErSi2 O7, polymorphs synthesized by high‐temperature flux crystal growth were determined by single‐crystal X‐ray diffraction analysis. Powder X‐ray diffraction, photoluminescence spectroscopy and scanning electron microscopy equipped with an energy dispersive X‐ray spectrometer elucidated differences between the two polymorphs. Abstract : Two polymorphs of tripotassium erbium disilicate, K3 ErSi2 O7, were synthesized by high‐temperature flux crystal growth during the exploration of the flux technique for growing new alkali rare‐earth elements (REE) containing silicates. Their crystal structures were determined by single‐crystal X‐ray diffraction analysis. One of them (denoted1 ) crystallizes in the space group P 63 / mmc and is isostructural with disilicates K3 LuSi2 O7, K3 ScSi2 O7 and K3 YSi2 O7, while the other (denoted2 ) crystallizes in the space group P 63 / mcm and is isostructural with disilicates K3 NdSi2 O7, K3 REESi2 O7 (REE = Gd–Yb), K3 YSi2 O7, K3 (Y0.9 Dy0.1 )Si2 O7 and K3 SmSi2 O7 . In the crystal structure of polymorph1, the Er cations are in an almost perfect octahedral coordination, while in the crystal structure of polymorph2, part of the Er cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. Sharing six corners, disilicate Si2 O7 groups in the crystal structure of polymorph1 link six ErO6 octahedra, forming a three‐dimensional network and nine‐coordinated potassium cations are located in its holes. In the crystal structure of polymorph2, the disilicate Si2 O7 groups connect four ErO6 octahedra, as well as one ErO6 trigonal prism. Three differently coordinated potassium cations are situated between them. Different site symmetries of the erbium cations in the crystal structures of polymorphs1 and2 affect their photoluminescence properties. Only polymorph2 exhibits luminescence. Intense narrow lines in the emission spectrum are a result of the 4 f –4 f transition. The green emission line at 560 nm is the result of the Er 3+ transition 4 S3/2 → 4 I15/2, and the luminescence line at 690 nm is the result of a 4 F9/2 → 4 I15/2 transition. The crystal morphologies of the two polymorphs are similar. Crystals of polymorph1 are in the form of a hexagonal prism in combination with a hexagonal base, while crystals of polymorph2 contain a dihexagonal prism in combination with a hexagonal base, although poorly developed faces of the dihexagonal pyramid can also be noticed.