Effect of annealing temperature on Eu²⁺ and Eu³⁺ ratios in AlN:Eu thin films

Eu-doped aluminum nitride (AlN:Eu) thin films were fabricated and characterized in a way of white light generation. AlN exhibits blue luminescence originating from defect levels. Furthermore, Eu²⁺ demonstrates green luminescence, while Eu³⁺ emits red light. Consequently, white luminescence is anticipated in Eu-doped AIN thin films. The concept is to control the ratio of Eu²⁺/Eu³⁺ in the thin film to vary the emission colors. We aimed to manipulate the Eu valence ratio in AIN:Eu thin films by changing the annealing temperature and examining the resultant luminescence characteristics. Our findings revealed an increase in defect-related luminescence in AIN samples annealed at higher temperatures, along with a rise in the Eu²⁺ fraction. We explore these outcomes in relation to the structural models surrounding Al and Eu ions, as elaborated in the main text.