Direct mechanochemical synthesis of CaMoO4 and Dy3+ doped CaMoO4 nanoparticles and their photoluminescent properties

Abstract

Calcium molybdate (CaMoO4) and Dy3+ doped CaMoO4 (Dy3+ = 0.5, 1, 1.5, 2 and 2.5 at.%) nanoparticles were successfully obtained by mechanochemical approach. The influence of Dy3+ ion concentration on the structure, morphology, and photoluminescent properties were investigated. The CaMoO4 and Dy3+ doped CaMoO4 phases with tetragonal structure were completely prepared after 30 min milling time with applied milling speed of 850 rpm. TEM analysis shows that the synthesized samples consist of mainly spherical particles with narrow particle size distribution. According to both XRD and TEM analysis, the average particles size is below 40 nm. The UV–vis absorption spectra show one peak at 240–245 nm. The calculated optical band gap of pure CaMoO4 is 3.96 eV and it decreases to 3.65 eV with increasing the concentration of Dy3+ ion up to 2.5 at %. The excitation spectra of the Dy3+-doped CaMoO4 samples contain absorption peaks corresponding to the MoO4 group and to the Dy3+ ion. The green and blue light emissions were observed for pure CaMoO4 and Dy3+ doped CaMoO4 samples under different wavelengths excitation (250 and 350 nm) typical for absorption of the host matrix. Emission spectra of all doped powders consist of the characteristic peaks of Dy3+ in the blue (∼480 nm) and yellow (∼575 nm) regions which are assigned to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. The weak peak at 660 nm also is observed due to 4F9/2 → 6H11/2 transition of Dy3+ ion. The highest photoluminescence emission intensity was detected when the sample is doped with 1.5 at.% Dy3+ concentration. It was found that the color coordinates (x and y) of 1.5 at.% and 2 at.% Dy3+-doped CaMoO4 fall close to the white light region in the CIE diagram. The results indicate that the mechanochemically obtained Dy3+ doped CaMoO4 nanoparticles can find application in different optical instruments.