Blue upconversion emission from Tm3+ sensitized by Nd3+ in aluminum oxide crystalline ceramic powders

Upconversion (UC) emission in thulium (Tm3+) and neodymium (Nd3+) co-doped aluminum oxide ceramic powders prepared by combustion synthesis was investigated at room temperature using a continuous wave laser operating at 800 nm. Our sample containing Tm3+ (1 wt.%) did not show any UC emission but our sample co-doped with Tm3+ and Nd3+ in 1:2 wt.% proportion presented blue (∼480 nm) UC intensity more than one order of magnitude larger than our sample co-doped with Tm3+ and Nd3+ in 1:1 wt.% proportion. X-ray diffraction data showed the presence of α-Al2O3 and REAlO3 (RE=Tm or Nd) crystalline phases in co-doped powders, while the singly doped powder has only α-Al2O3 phase. Our results show that the UC emission efficiency of Tm3+ and the host crystalline structure can be tailored by manipulating the Nd3+ doping concentration.