Cold white light generation from hafnium oxide films activated with Ce³⁺, Tb³⁺, and Mn²⁺ ions

Hafnium oxide films doubly doped with CeCl₃ and TbCl₃ and triply doped with CeCl₃, TbCl₃, and MnCl₂ were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The green and yellow emissions of Tb³⁺ ions and the yellow-red emission of Mn²⁺ ions can be generated upon ultraviolet (UV) excitation via a nonradiative energy transfer from Ce³⁺ to Tb³⁺ and Ce³⁺ to Mn²⁺. In the doubly doped film Ce³⁺ → Tb³⁺ energy transfer via an electric dipole–quadrupole interaction appears to be the most probable transfer mechanism; the efficiency of this transfer is about 81% upon excitation at 270 nm. In the HfO₂ films activated with Ce³⁺, Tb³⁺, and Mn²⁺ the efficiency of energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions is enhanced by increasing the Mn²⁺ concentration, up to about 76% for the film with the highest manganese content (1.6 at.%). In addition, it is demonstrated that these triply doped films can generate cold white light emission upon excitation at 270 nm (peak emission wave length of an AlGaN/GaN-based LEDs).