Structural features and photoluminescence behaviors of color-temperature tunable (Gd,Y)3Al5O12:Ce3+/Cr3+ phosphors with varying compositions

We designed a chemical coprecipitation method to obtain hollow round precursors with hydrated basic carbonate sulfate structures; these precursors were then thermally treated to yield near-spherical (Gd _{0.99- x}Y _xCe _0.01) ₃(Al _{1- y}Cr _y) ₅O ₁₂ ( x = 0.25‒0.99, y = 0‒0.02) garnet phosphors. With ≥35 at.% Y ³⁺ substitution for Gd ³⁺, relatively stable garnet crystal structures could be obtained. More Y ³⁺ addition led to shrinkage of the unit cell; however, Cr ³⁺ doping caused crystal lattice expansion. The Ce ³⁺ activated phosphor exhibited a strong broad emission band at 500‒700 nm arising from ²D _3/2→ ²F _5/2,7/2 transitions of Ce ³⁺, while the Cr ³⁺ codoped sample presented three additional red emission bands in the range of 675‒725 nm arrtibuted to ²E _g (2g) → ⁴A _2g (4f) transition of Cr ³⁺ and some phonon sidebands. At a constant Ce ³⁺ content of 1 at.%, the Cr ³⁺ emission intensity increased to maximum at 0.5 at.% Cr ³⁺ concentration via efficient energy transfer from Ce ³⁺ to Cr ³⁺, which was attributed to electric multipole interactions such as dipole-quadrupole interactions. A higher particle calcination temperature significantly enhanced the luminescence intensity as well as caused spectral redshifts via correlation-induced enhancement of the crystal field splitting. The color temperature could be tailored in a wide range of ∼5075‒3374 K by controlling both Y ³⁺/Gd ³⁺ ratio and calcination temperature. The Cr ³⁺ addition further shortened the fluorescence lifetime for the 556 nm emission of Ce ³⁺.