Modulating Optical Properties through Cation Substitution: Composition-Property Relationships in MI3MIIIP3O9N:Eu2+ (MI=Na, K; MIII=Al, Ga, In)

Developing phosphors with narrow photoluminescence emission peaks and high chromatic stability holds significant importance in light-emitting diode (LED) display technologies, where a wide color gamut is essential to achieve the Rec. 2020 specifications. This research focuses on the optical properties of a solid solution: M^I_2.97Eu_0.015M^IIIP₃O₉N [M^I=Na, K; M^III=Al, (Al_0.75Ga_0.25), (Al_0.5Ga_0.5), (Al_0.25Ga_0.75), Ga, (Ga_0.75In_0.25), (Ga_0.5In_0.5)] to understand how the narrow-emitting photoluminescence in K₃AlP₃O₉N:Eu²⁺ can evolve during host structure cation substitution. Photoluminescence measurements at low temperature (15 K) support that Eu²⁺ replaces three crystallographically independent Na⁺ sites in Na_2.97Eu_0.015AlP₃O₉N, similar to the parent K⁺ phosphor, but substituting Ga³⁺ and In³⁺ for Al³⁺ leads to a change in Eu²⁺ site preference, narrowing the full-width-at-half-maximum (fwhm) of the emission peak. The chromatic stability and photoluminescence quantum yield are also enhanced with higher Ga³⁺ content in the host but not with In³⁺. Thermoluminescence analysis indicates the relationship between trap states and the enhanced quantum yield with Ga³⁺ leads to the series’ best performance. The analysis of the M^I_2.97Eu_0.015M^IIIP₃O₉N series offers insight into the potential method for modulating optical properties with cation substitution in the host structure.