Highly enhanced f–f transitions of Eu3+ in La2O3 phosphor via citric acid and poly (ethylene glycol) precursor route

The luminescent material europium-activated La2O3 have been prepared by the citric acid and poly (ethylene glycol) (PEG) precursor route. Their structures and optical properties were characterized by FT-IR spectrum, X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), UV–vis spectroscopy, and photoluminescence (PL) spectra, respectively. The results show considerable enhancement of the photoluminescence, especially the Eu3+ f–f transition excitation lines and the charge transfer band (CT). The samples can exhibit strong red emission centered at 626 nm excited at either the CT band (300 nm) or the Eu3+ f–f transition (396 nm), suggesting the potential application as the red phosphors for ultraviolet light-emitting diodes (LEDs), which can be attributed to the 5D0→7F2 transition of Eu3+. The remarkable enhancement of color purity of red emission and the concentration quenching of Eu3+ in La2O3 were also observed with increasing Eu3+ doped concentration.