EFFECTS OF ION Cr3+ CONCENTRATION ON THE OPTICAL PROPERTIES OF ZnAl2O4:Mn2+ PHOSPHOR POWDER VIA SOL-GEL METHOD

Abstract

Green and red emitting co-doped Mn²⁺ and Cr³⁺ ions ZnAl₂O₄ phosphor powders were successfully manufactured via sol-gel method combined with air annealing at different temperatures. The results of X-ray diffraction show that the ZnAl₂O₄ material has the best crystal quality when heated at 1400 ^oC. FE-SEM imaging results show that the powder with particle size increases as the sintering temperature increases, at a temperature of 1400 ^oC the particle size is distributed from several tens of nanometers to hundred nanometers. The results of the fluorescence spectra showed that the material emitted strongly in the reddish-red area and a weak emission in the green light. Weak emission with peak fluorescence at 511 nm is attributed to the transition of Mn^{2 +} ions from the state of ⁴T₁ → ⁶A₁ in ZnAl₂O₄host. Strong emission in red and far red-light region at 686 nm emission peak due to the energy transfer of Ce³⁺ ions from ²T_2g ®⁴A_2g in ZnAl₂O₄ crystal lattice. Fluorescence excitation spectra with a peak of 686 nm showed that the material is most strongly absorbed at the excitation wavelengths of 395 nm and 535 nm corresponding to the transfer of energy of Cr³⁺ ions from the ⁴A_2g ground state to the excited states of ⁴T_1g and ⁴T_2g. The best emitting phosphor is the 0.5% Mn²⁺ and 0.5% Cr³⁺ ions doped ZnAl₂O₄ sample sintered for 2 hours, at 1400 ^oC in air conditions.