Synthesis of garnet-type Mn⁴⁺-activated Y₃(Al,Ga)₅O₁₂ and (Y,Gd)₃Al₅O₁₂ phosphors with controlled emission by cation substitution

Ga- and Gd-substituted garnet-type Y3Al5O12:Mn4+ phosphors, Y3(Al1−xGax)5O12:Mn4+ and (Y1−yGdy)3Al5O12:Mn4+, were synthesized by a conventional solid-state reaction to elucidate the relationship between the emission and the local structure of the activator in the host material. Completely substituted Y3(Al1−xGax)5O12 and ∼80 % substituted (Y1−yGdy)3Al5O12 (y ≤ ∼0.8) solid solutions have been produced. The lattice parameters of the garnet-type solid solutions increased linearly with the substitution of Ga and Gd for Al and Y sites, respectively. The emission peak attributed to the Mn4+ luminescence center of their garnet-type solid solutions shifted toward a longer wavelength side by substituting Ga and Gd. The emission peak wavelength of the Mn4+-activated garnet-type solid solutions increased almost linearly with increasing the average bond length between the cation and anion in the dodecahedral sites. The dodecahedral site in the garnet structure is edge-sharing with the octahedral site where Mn4+ exists. These results indicate that the emission wavelength can be controlled by changing the local structure around Mn4+ due to the cation substitution of coordination polyhedra neighboring Mn4+ coordination polyhedra.