Template-Guided Crystal Chemical Design of Eu2+-Activated La2Ca3[Si4N4O8] Oxonitridosilicate Phosphor

Template-guided crystal-chemical design offers a route to oxonitridosilicates, but transfer of an oxide topology requires compatible cation coordination and charge balance. Here, we report the synthesis and structural characterization of the 6-ring host La2Ca3[Si4N4O8], designed by considering [SiN]+ for [AlO]+ substitution in the Ca3[Al2O6] template together with aliovalent La3+/Ca2+ substitution. The idealized structural description contains isolated rings of corner-sharing [SiN2O2] tetrahedra and partially occupied or vacant cation sites. The nominal substitution scheme, 3Ca2+ → 2La3+ + VCa, provides a charge-balanced crystal-chemical rationale for the cation deficiency. Theoretical calculations reveal that the aliovalent substitution induces cation vacancies accompanied by local charge redistribution and coordination rearrangement, which may alleviate the lattice strain arising from the cation-size mismatch. Eu2+ activation produces broadband orange emission centered near 600 nm, with a reported photoluminescence quantum yield of 29.3%. The phosphor was further applied to a white LED by combining it with multiple phosphors. This work illustrates how cation composition and occupancy can be considered alongside the topology in template-guided exploratory synthesis.