Effect of synthesis conditions on the structural characteristics and luminescence properties of Y0.9Eu0.1V1−xCrxO4 (0 ≤ x ≤ 0.5) nanopowders

Y0.9Eu0.1V1−xCrxO4 (0 ≤ x ≤ 0.5) nanophosphors were synthesized under acid conditions (pH = 2) by a one-step sol-gel process followed by a thermal treatment at 843 K in oxygen flow. The obtained nanopowders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and by Raman and photoluminescence (PL) spectroscopies in a confocal microscope. The influence of pH on the structural characteristics and luminescence properties of the nanophospors was also assessed. XRD measurements reveal a progressive loss of crystallinity as chromium substitutes for vanadium in the samples. Such replacement induces a progressive broadening of the Raman peaks as the Cr content increases, evidencing a certain structural distortion involving different (VO4)3− groups due to the insertion of Cr5+ ions into the host. TEM images of the obtained nanopowders show changes in the particle shape and size of samples grown a different pH values. The addition of chromium hampers an effective energy transfer from the vanadate groups to the Eu3+ ions. This results in a strong decrease of the PL emission intensity corresponding to the intraionic transitions of this rare earth, irrespective of the synthesis conditions of the nanopowders.