Combinatorial chemistry of oxynitride phosphors and discovery of a novel phosphor for use in light emitting diodes, Ca1.5Ba0.5Si5N6O3:Eu2+

Abstract

Solid-state combinatorial chemistry (combi-chem) has been proven to be a versatile tool for the discovery of novel phosphors in the multi-compositional (oxy)nitride search space. Since the advent of a unique solid-state combi-chem technique involving heuristic optimization strategies such as a non-dominated sorting genetic algorithm (NSGA), we have discovered several novel phosphors. The present investigation was focused on a phosphor that was previously discovered using this technique, but was incompletely identified, on pinpointing the optimum processing composition of the discovered phosphor exhibiting promising PL properties with the assistance of particle swarm optimization (PSO), and on identifying the exact structure based on synchrotron X-ray diffraction data. The exact stoichiometry of the discovered, unknown phosphor was determined to be Ca_1.5Ba_0.5Si₅N₆O₃:Eu²⁺ and was indexed as a monoclinic lattice in the Cm space group, with lattice parameters a = 7.07033(2) Å, b = 23.86709(7) Å, c = 4.825304(15) Å, and β = 109.0647(2)°. A structural determination process that involved a direct method, simulated annealing, and Rietveld refinement revealed that the exact structure of Ca_1.5Ba_0.5Si₅N₆O₃:Eu²⁺ was somewhat a composite structure combining the well known CaSi₂N₂O₂:Eu²⁺ and BaSi₆N₈O:Eu²⁺ structures. The discovered phosphor showed a broad-band type emission of yellow-red light under UV and blue light excitations, which makes it a promising candidate for practical use in LED applications.