Towards White Light Emission Through Metal-to-Metal Charge Transfer (MMCT) Effect in Bi Activated CaYTiZrGaO (0≤m≤2) Garnets.

Herein, we report the high-temperature solid-state synthesis and intriguing optical features of Bi/Ln doped CaYTiGaO (CYT). The optical properties of CYT were fine-tuned by judiciously substituting Zr ions at Ti sites and Bi, Ln ions at Y sites. All these compounds are crystallized in a cubic crystal system with an Ia-3d (no. 230) space group. The Bi 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:Bi was co-doped with blue emissive Tm to obtain an excitation wavelength-dependent color tuneable white light phosphor CYT:TmBi. Substituting Zr ions in place of Ti ions in CYT gave rise to CYTZ (CaYTiZrGaO), which upon doping with Bi gave CaYZrGaO:Bi (CYZ:Bi) and they exhibit the P→S emission in the violet-indigo region ( λ=395 nm; λ=315 nm). On co-doping CYTZ:Bix with Sm ions produced white light emissive CaYTiZrGaO:Bi; Sm, (CYTZ:Bi; Sm). 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 observed optical features of these compounds. The optical features of CYT:Bi, were explored for potential applications in secret writing.