Photoluminescence and afterglow of Yb2+doped CaAl2O4

The photoluminescence (PL) and afterglow properties of Yb2+ doped CaAl2O4 phosphors (0-2.0 x 104 ppm) are investigated. The 4f14-4f135d1 transitions of Yb2+ dopant are evidenced by a number of sharp lines in the excitation and emission spectra of Yb2+ doped CaAl2O4. As a contrast, the host emission of Yb2+ doped CaAl2O4 is characteristic of a broadband PL spectrum which can be deconvoluted into three overlapped subbands: an ultraviolet subband peaking at 3.30 eV (375.8 nm), a blue subband peaking at 2.81 eV (441.3 nm) and a green subband peaking at 2.35 eV (527.7 nm). The afterglow spectrum of Yb2+ doped CaAl2O4 consists of three discrete subbands: an ultraviolet subband centered at around 3.54 eV (350 nm), a blue subband centered at around 2.82 eV (440 nm) and a green subband centered at about 2.30 eV (540 nm). Depending on their intensities of the afterglow subbands, the perception color of the afterglow of Yb2+ doped CaAl2O4 evolves from blue to green, and the afterglow of Yb2+ doped CaAl2O4 lasts for 86 min at the optimal doping level of 20 ppm. Our results demonstrate that: (i) the ultraviolet and the blue afterglow subbands of the phosphor originate from oxygen and cation vacancies in CaAl2O4; (ii) the green afterglow (PL) subband of Yb2+ doped CaAl2O4 originates from Mn2+ impurity in CaAl2O4; and (iii) instead of a luminescence center of afterglow, Yb2+ works as a luminescence center of PL and sensitizes CaAl2O4 by enhancing the ultraviolet light harvesting efficiency of the host.