The influence of Cr³⁺ concentration on the structure and photoluminescence of MgAl₂O₄:0.1% Eu³⁺, x% Cr³⁺ (0≤x≤0.15%)nanophosphor synthesized by sol-gel process

MgAl₂O₄ and 0.1% Eu³⁺, x% Cr³⁺ co-activated nano-phosphors were successfully prepared using the sol-gel method. The co-activator (Cr³⁺) mol% was varied at a range of 0≤x≤0.15%. All annealed samples consist of the pure cubic MgAl₂O₄ structure. Varying the Cr³⁺ concentration influenced the surface morphology of the nano-phosphor. The host, 0.1% Cr³⁺ and 0.1% Eu³⁺ activated nanophosphor emits at different wavelengths. The emission peak at 398 nm is attributed to the defect within the host. The emission peaks at 403, 565 and 694 nm are attributed to arise from the Cr³⁺ transitions from ⁴T₁ → ⁴A, ⁴T₂ → ⁴A ₂ and ²E → ⁴A₂, respectively. The emission peaks at 574 and 619 nm are respectively attributed to the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions in the Eu³⁺ ion. No evidence of energy transfer was observed. The emission colour could be turned by varying the co-activator concentration and excitation wavelength.