Towards White Light Emission Through Metal-to-Metal Charge Transfer (MMCT) Effect in Bi3+ Activated Ca2YTi2-mZrmGa3O12 (0 ≤ m ≤ 2) Garnets

Herein, we report the high-temperature solid-state synthesis and intriguing optical features of Bi3+/Ln3+ doped Ca2YTi2Ga3O12 (CYT). The optical properties of CYT were fine-tuned by judiciously substituting Zr4+ ions at Ti4+ sites and Bi3+, Ln3+ ions at Y3+ sites. All these compounds are crystallized in a cubic crystal system with an Ia-3d (no. 230) space group. The Bi3+ doped systems showed a broad photoluminescence (PL) band in the yellow-orange region centered at ~552 nm from the metal-to-metal charge transfer state (MMCT). The yellow-orange emissive CYT:Bix was co-doped with blue emissive Tm3+ to obtain an excitation wavelength-dependent color tuneable white light phosphor CYT:Tm0.02Bi0.012. Substituting Zr4+ ions in place of Ti4+ ions in CYT gave rise to CYTZ (Ca2YTi2-mZrmGa3O12), which upon doping with Bi gave Ca2YZr2Ga3O12:Bix (CYZ:Bix) and they exhibit the 3P0,1 → 1S0 emission in the violet-indigo region (λem = 395 nm; λex = 315 nm). On co-doping CYTZ:Bix with Sm3+ ions produced white light emissive Ca2YTi0.1Zr1.9Ga3O12:Bi3+; Sm3+, (CYTZ:Bi3+; Sm3+). CYT:Bix showed slower (microsecond) PL decay than the CYZ:Bix (nanosecond). The crystal structure, steady state, and time-resolved optical studies, and semiempirical calculations were employed to rationalize the optical features. The optical features of CYT:Bi0.1, were explored for potential applications in secret writing.