Tunable photoluminescence and energy transfer of Eu3+,Ho3+-doped Ca0.05Y1.93-xO2 nanophosphors for warm white LEDs applications

Abstract

A series of Eu³⁺ ions doped Ca_0.05Y_1.93-xO₃:0.02Ho³⁺ (CYO:Ho³⁺,xEu³⁺) nanophosphors having multicolour tuneability have been synthesised by following a simplistic solution combustion approach. The synthesised samples have been characterised by employing X-ray diffraction (XRD), Transmission electron microscope (TEM), and Fourier transforms infrared spectroscopy (FTIR). The optical properties have been engrossed by UV-visible and photoluminescent excitation and emission spectra, and decay lifetimes measurements. The characteristic emission, which occurs due to the f-f transition of Ho³⁺ and Eu³⁺ has been observed in emission spectra with excitation of 448 nm. By adjusting the doping ratio of Ho³⁺/Eu³⁺, the as-synthesized nanophosphor accomplishes multicolour tunability from green-yellow to red. Emission spectra and decay lifetime curve recommend dipole-dipole interaction causes energy transfer from Ho³⁺ → Eu³⁺. The energy transfer process from Ho³⁺ to Eu³⁺ has been confirmed through electric dipole-dipole interaction with critical distance 15.146 Å. Moreover, temperature dependent emission spectra show the high thermal stability with an activation energy ⁓ 0.21 eV, with the quantum efficiency of 83.6%. CIE coordinate illustrates that the singly doped Ho³⁺ and Eu³⁺ lie in the green and red region, respectively, while the as-synthesized CYO:Ho³⁺,xEu³⁺shows tunability from green to red with low CCT and high colour purity values. Hence, the CYO:Ho³⁺,xEu³⁺nanophosphor may be a near-UV excited multicolour colour-tunable pertinent candidate with potential prospects for multicolour- display and near-ultraviolet lighting applications.