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Accessing (Ba 1– x Sr x )Al 2 Si 2 O 8 :Eu Phosphors for Solid State White Lighting via Microwave‐assisted Preparation: Tuning Emission Color by Coordination Environment
Author(s) -
Brgoch Jakoah,
Kloß Simon D.,
Denault Kristin A.,
Seshadri Ram
Publication year - 2014
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201400003
Subject(s) - monoclinic crystal system , luminescence , crystallography , materials science , phosphor , phase (matter) , crystal structure , solid solution , barium , hexagonal phase , bond length , analytical chemistry (journal) , hexagonal crystal system , chemistry , optoelectronics , organic chemistry , chromatography , metallurgy
The preparation of Eu 2+ ‐substituted barium aluminum silicates is achieved using a rapid microwave‐assisted preparation. The phase evolution of two BaAl 2 Si 2 O 8 :Eu 2+ polymorphs, the higher temperature hexagonal phase (hexacelsian), and the lower temperature monoclinic phase (celsian), is explored by varying the ramp time and soak time. This preparation method significantly reduces the reaction time needed to form these phases compared to conventional solid state routes. The luminescent properties of the two phases are identified under UV excitation with the hexagonal phase emitting in the UV region ( λ em = 372 nm) and the monoclinic phase emitting in the blue region ( λ em = 438 nm). The differences in optical properties of the two polymorphs are correlated to the coordination number and arrangement of the alkali earth site. The optical properties of the monoclinic phase can be further tuned through the substitution of Sr 2+ , forming the solid solution (Ba 1– x Sr x )Al 2 Si 2 O 8 :Eu 2+ . Changes in the crystal structure due to Sr 2+ substitution produce a surprising blue‐shift in the emission spectrum, which is explained by a greater dispersion of bond lengths in the (Ba/Sr)–O polyhedra. The entire monoclinic solid solution exhibits excellent quantum yields of nearly 90 %, owing to the structural rigidity provided by the highly connected tetrahedral network.