Polyhedral distortion control of unusual photoluminescence color tuning in garnet phosphors via cation substitution

Controllable luminescence properties for phosphors can be realized through optimum composition design and structural tuning. The local microstructural evolutions and luminescent properties of Y3Al5O12:Ce3+ via the substitution of the cations Ga3+/Sc3+ for Al3+ are investigated. The emission spectrum of Y3Al2-xGaxAl3O12:Ce3+ has a blueshift from 559 to 531 nm with the substitution Ga3+ for Al3+. This outcome can be attributed to a lengthened Ce-O bond, which leads to a smaller crystal splitting. In the above ending composition Y3Ga2Al3O12:Ce3+, an unusual redshift from 531 to 545 nm can be observed by further replacing Ga3+ with the larger Sc3+. Combining first-principles calculations and the position of energy level analysis, introduced Sc3+ into Y3Al5O12 lattices can cause a sharp increase in (Ce-O-8) polyhedron distortion, leading to a larger additional distorted crystal-field splitting of eg, levels compared to that of Ga3+ dopant. Moreover, a relatively larger electronegativity of Sc3+ can enhance the nephelauxetic effect and further lower the lowest 5d level. These two factors are responsible for the unusual redshift. A formula was generalized to describe the polyhedral distortion that can explain the unusual redshift very well. This work gives a clear relationship between the composition, structure and photoluminescent properties in garnet-type phosphors and provides a guide for targeted optimization of photoluminescent properties in other systems.