Mechanism for bifurcation of broadband luminescence spectra from Ce3+ ions at dodecahedral sites in garnets {CaY2}[M2](Al2Si)O12 (MÂ = Al, Ga, Sc)

- Ce3+ doped multicomponent garnets CaY2M2Al2SiO12 (M = Al, Ga, Sc) were synthesized.
- Broadband luminescence from two optical Ce3+ centers is detected in each garnet.
- Two centers are related to Ca2+ and Y3+ at the dodecahedral site in garnet structure.
- Spectral bifurcation leads to increasing the Stokes shift of Ce3+ luminescence.
- CaY2Al4SiO12:Ce3+ phosphor has high luminescence quenching temperature T1/2 = 635 K.

Cerium doped CaY2Al4SiO12, CaY2Ga2Al2SiO12 and CaY2Sc2Al2SiO12 garnet phosphors have been synthesized by using a high temperature solid-state reaction method and studied by optical spectroscopy techniques in the wide temperature range. It has been revealed that the emission spectra from all the synthesized samples can be well represented as the sum of spectral bands due to the 5d - 4f transitions of two optical Ce3+ centers having different local environment. It is proposed that these two centers arise due to various types of distortions caused by crystal chemical differences between calcium and yttrium ions located at the dodecahedral crystallographic site in the garnet structure. Such a dual-mode distortion site leads to increasing the Stokes shift of Ce3+ emission spectra for the studied garnets in comparison with YAG:Ce3+. The phosphor CaY2Al4SiO12:Ce3+ shows a weak blue shift of Ce3+ luminescence compared to YAG:Ce3+ and demonstrates excellent thermal stability on temperature quenching effects by manifesting the thermal quenching temperature T1/2 at 635 K. Substitution of Al3+ by larger cations Ga3+ or Sc3+ has resulted in the additional blue shift of the luminescence spectrum and the appearance of strong thermal quenching.