Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications
Priti Singh, Hirdyesh Mishra, S. Bahadur
Abstract
Abstract 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, Dy 3+ , Ho 3+ singly doped and Dy 3+ /Ho 3+ co-doped CaTiO 3 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 Dy 3+ doped CaTiO 3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho 3+ doped CaTiO 3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy 3+ and Ho 3+ were co-doped simultaneously in CaTiO 3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy 3+ to Ho 3+ with 367 nm and from Ho 3+ to Dy 3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO 3 :4Dy 3+ /3Ho 3+ and CaTiO 3 :3Ho 3+ /5Dy 3+ 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 4 F 9/2 level of Dy 3+ ion and 5 S 2 level of Ho 3+ ion is decreased in presence of Ho 3+ and Dy 3+ ions, respectively. This is due to energy transfer from Dy 3+ to Ho 3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO 3 :4Dy 3+ /2Ho 3+ 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 CaTiO 3 :4Dy 3+ , CaTiO 3 :4Dy 3+ /2Ho 3+ and CaTiO 3 :3Ho 3+ phosphors, respectively. Hence, Dy 3+ , Ho 3+ singly doped and Dy 3+ /Ho 3+ co-doped CaTiO 3 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.