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

Abstract

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 (Gd0.99-xYxCe0.01)3(Al1-yCry)5O12 (x = 0.25‒0.99, y = 0‒0.02) garnet phosphors. With ≥35 at.% Y3+ substitution for Gd3+, relatively stable garnet crystal structures could be obtained. More Y3+ addition led to shrinkage of the unit cell; however, Cr3+ doping caused crystal lattice expansion. The Ce3+ activated phosphor exhibited a strong broad emission band at 500‒700 nm arising from 2D3/2→ 2F5/2,7/2 transitions of Ce3+, while the Cr3+ codoped sample presented three additional red emission bands in the range of 675‒725 nm arrtibuted to 2Eg (2g) →4A2g (4f) transition of Cr3+ and some phonon sidebands. At a constant Ce3+ content of 1 at.%, the Cr3+ emission intensity increased to maximum at 0.5 at.% Cr3+ concentration via efficient energy transfer from Ce3+ to Cr3+, 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 Y3+/Gd3+ ratio and calcination temperature. The Cr3+ addition further shortened the fluorescence lifetime for the 556 nm emission of Ce3+.