| Room temperature bright upconversion (UC) emission in Yb3+-Er3+ ions doped 12CaO·7Al2O3 (C12A7: Yb-Er) powder prepared by the sol-gel method was observed under single-wavelength diode laser excitation of 980 nm.The high light developing yellow or green color consists of the violet, blue green, and red (408, 483,520/540, and 660 nm) UC radiations which correspond to the transitions 2H9/2→4I15/2, 4F7/2→4I15/2, 2H11/2/4S3/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions, respectively.X-ray diffraction patterns and SEM observations showed that C12A7:Yb-Er powders with the grain size of 200-300 nm were synthesized, demonstrate that the UC emission is mainly from bulk effect in C12A7: Yb-Er particles rather than surface effect. A green band integrated intensity to the others bands integrated intensity ratio (R) parameter was introduced, defined as the UC intensity ratio of the green bands to the other detected excitation bands, and R values approximately 1-14 were experimentally obtained. The R has decreased with an increase of concentration of Yb3+ ions. Yb3+ ions play an important role in generating and tailoring for the UC spectrum.
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