ReviewAnnealing effects on structural and luminescence properties of red Eu3+-doped Y2O3 nanophosphors prepared by sol-gel method

•Europium trivalent (Eu3+) doped Y2O3 powders were synthesized by sol-gel method, followed by annealing at different temperatures, between 300 °C and 1000 °C.•XRD results revealed that at 300 °C the Eu3+-doped Y2O3 is already crystallized.•The charge transfer band (CTB) position evolution in function of grain size (annealing temperature) is studied. It presents a redshift for small grain sizes.•A modified Jørgensen expression is proposed based on Eu3+-O2− distance and the coordination number variations to explain the CTB redshift.

Europium trivalent (Eu3+) doped Y2O3 powders were synthesized by the sol-gel method, followed by annealing at different temperatures, between 300 °C and 1000 °C. The powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence spectroscopy. Effects of annealing treatment on structural, morphological and photoluminescence properties of Eu3+ doped Y2O3 are studied and discussed. XRD results revealed that the Eu3+ doped Y2O3 crystallizes in pure body centered cubic (bcc) phase and at 300 °C, the product is already crystallized. The average crystallite size, found by XRD analysis, increases from 12 to 30 nm as annealing temperature increases. Moreover, different morphology is observed when annealing temperature changes. Also, FESEM shows that the particle size increases with increasing annealing temperature and presents regular spherical shapes. Intense red emissions at 610 and 588 nm assigned to forced electric dipole 5D0→7F2 and to magnetic dipole 5D0→7F1 transitions, respectively, of Eu3+ ion are observed. The emission becomes more intense for higher annealing temperature, which is related to the improvement of crystalline quality. In this study, more attention has been paid to the investigation of the charge transfer band (CTB) position evolution with crystallite size, which depends on the annealing temperature. It was found that when annealing temperature is decreased (small crystallite size) the CTB position presents a redshift. To explain this redshift, modified Jørgensen expression is proposed based on Eu3+-O2− distance and the coordination number variations.