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Material Properties and Structural Characterization of M 3 Si 6 O 12 N 2 :Eu 2+ (M=Ba, Sr)—A Comprehensive Study on a Promising Green Phosphor for pc‐LEDs
Author(s) -
Braun Cordula,
Seibald Markus,
Börger Saskia L.,
Oeckler Oliver,
Boyko Teak D.,
Moewes Alexander,
Miehe Gerhard,
Tücks Andreas,
Schnick Wolfgang
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000660
Subject(s) - luminescence , phosphor , crystallography , crystal structure , materials science , full width at half maximum , silicon , analytical chemistry (journal) , chemistry , optoelectronics , chromatography , metallurgy
The efficient green phosphor Ba 3 Si 6 O 12 N 2 :Eu 2+ and its solid‐solution series Ba 3− x Sr x Si 6 O 12 N 2 (with x ≈0.4 and 1) were synthesized in a radio‐frequency furnace under nitrogen atmosphere at temperatures up to 1425 °C. The crystal structure (Ba 3 Si 6 O 12 N 2 , space group P $\bar 3$ (no. 147), a =7.5218(1), c =6.4684(1) Å, wR 2=0.048, Z =1) has been solved and refined on the basis of both single‐crystal and powder X‐ray diffraction data. Ba 3 Si 6 O 12 N 2 :Eu 2+ is a layer‐like oxonitridosilicate and consists of vertex‐sharing SiO 3 N‐tetrahedra forming 6er‐ and 4er‐rings as fundamental building units (FBU). The nitrogen atoms are connected to three silicon atoms (N3), while the oxygen atoms are either terminally bound (O1) or bridge two silicon atoms (O2) (numbers in superscripted square brackets after atoms indicate the coordination number of the atom in question). Two crystallographically independent Ba 2+ sites are situated between the silicate layers. Luminescence investigations have shown that Ba 3 Si 6 O 12 N 2 :Eu 2+ exhibits excellent luminescence properties (emission maximum at ≈527 nm, full width at half maximum (FWHM) of ≈65 nm, low thermal quenching), which provides potential for industrial application in phosphor‐converted light‐emitting diodes (pc‐LEDs). In‐situ high‐pressure and high‐temperature investigations with synchrotron X‐ray diffraction indicate decomposition of Ba 3 Si 6 O 12 N 2 under these conditions. The band gap of Ba 3 Si 6 O 12 N 2 :Eu 2+ was measured to be 7.05±0.25 eV by means of X‐ray emission spectroscopy (XES) and X‐ray absorption near edge spectroscopy (XANES). This agrees well with calculated band gap of 6.93 eV using the mBJ‐GGA potential. Bonding to the Ba atoms is highly ionic with only the 4p 3/2 orbitals participating in covalent bonds. The valence band consists primarily of N and O p states and the conduction band contains primarily Ba d and f states with a small contribution from the N and O p states.