Multicolor tunable emission through energy transfer in Dy³⁺/Ho³⁺ co-doped CaTiO₃ phosphors with high thermal...

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED's and multicolor display devices. In this paper, Dy³⁺, Ho³⁺ singly doped and Dy³⁺/Ho³⁺ co-doped CaTiO₃ phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy³⁺ doped CaTiO₃ phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho³⁺ doped CaTiO₃ phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy³⁺ and Ho³⁺ were co-doped simultaneously in CaTiO₃ host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy³⁺ to Ho³⁺ with 367 nm and from Ho³⁺ to Dy³⁺ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO₃:4Dy³⁺/3Ho³⁺ and CaTiO₃:3Ho³⁺/5Dy³⁺ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of ⁴F_9/2 level of Dy³⁺ ion and ⁵S₂ level of Ho³⁺ ion is decreased in presence of Ho³⁺ and Dy³⁺ ions, respectively. This is due to energy transfer from Dy³⁺ to Ho³⁺ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO₃:4Dy³⁺/2Ho³⁺ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303-483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO₃:4Dy³⁺, CaTiO₃:4Dy³⁺/2Ho³⁺ and CaTiO₃:3Ho³⁺ phosphors, respectively. Hence, Dy³⁺, Ho³⁺ singly doped and Dy³⁺/Ho³⁺ co-doped CaTiO₃ phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED's and photodynamic therapy for the cancer treatment.