White light generation in Al2O3:Ce3+:Tb3+:Mn2+ films deposited by ultrasonic spray pyrolysis

Aluminium oxide (Al2O3) films doped with CeCl3, TbCl3 and MnCl2 were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The films were analysed using the X-ray diffraction technique and they exhibited a very broad band without any indication of crystallinity, typical of amorphous materials. Sensitization of Tb3+ and Mn2+ ions by Ce3+ ions gives rise to blue, green and red simultaneous emission when the film activated by such ions is excited with UV radiation. The overall efficiency of such energy transfer results to be about 85% upon excitation at 312 nm. Energy transfer from Ce3+ to Tb3+ ions through an electric dipole–quadrupole interaction mechanism appears to be more probable than the electric dipole–dipole one. A strong white light emission for the Al2O3:Ce3+(1.3 at.%):Tb3+(0.2 at.%):Mn2+(0.3 at.%) film under UV excitation is observed. The high efficiency of energy transfer from Ce3+ to Tb3+ and Mn2+ ions, resulting in cold white light emission (x = 0.30 and y = 0.32 chromaticity coordinates) makes the Ce3+, Tb3+ and Mn2+ triply doped Al2O3 film an interesting material for the design of efficient UV pumped phosphors for white light generation.