Zn(Al$_{1-x}$Cr$_x$)$_2$O$_4$ powders with Cr$^{3+}$ contents ranging from x = 0.005 to 0.3 have been synthesized by sol-gel method using the following precursors: zinc nitrate (Zn(NO$_3$)$_2\cdot6$H$_2$O), aluminium nitrate (Al(NO$_3$)$_3\cdot9$H$_2$O), chrome nitrate (Cr(NO$_3$)$_3\cdot9$H$_2$O), and citric acid. The effect of the Cr$^{3+}$ concentration on structural and optical properties of the synthesized samples has been studied. For the samples with low Cr$^{3+}$-dopant concentrations, the photoluminescent (PL) spectra consist of sharp lines assigned to the $^2$E($^2$G) $\to$ $^4$A$_2$($^4$F) transition of ions Cr$^{3+}$ in strong octahedral field. But for the samples with high Cr$^{3+}$-dopant concentrations, the PL spectra consist of a broad band centered at longer wavelengths assigned to the $^4$T$_2$($^4$F) $\to$ $^4$A$_2$($^4$F) transition of ions Cr$^{3+}$ in weak octahedral field.
