Concentration quenching of blue upconversion luminescence in Tm 3+ /Yb 3+ co-doped Gd 2 (WO 4 ) 3 phosphors under 980 and 808 nm excitation

Abstract

Abstract This paper reported on the upconversion (UC) spectroscopic properties of Tm 3+ /Yb 3+ codoped Gd 2 (WO 4 ) 3 phosphors synthesized by a traditional co-precipitation method upon excitation of 980 and 808 nm commercial available fiber lasers, respectively. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to characterize the crystal structure and morphology of the samples. Intense blue emission ( 1 G 4 → 3 H 6 ) and near-infrared (NIR) emission ( 3 H 4 → 3 H 6 ) as well as weak red emission ( 1 G 4 → 3 F 4 ) of Tm 3+ were observed under 980 nm excitation. The concentration quenching processes for blue and NIR emissions were discussed. The blue emission intensity has a cubic dependence on the fiber laser working current, indicating a three-photon process involved in blue UC emission. The blue emission and its concentration quenching process for Tm 3+ /Yb 3+ codoped Gd 2 (WO 4 ) 3 phosphors were also investigated under 808 nm excitation. Weak blue emission ( 1 D 2 → 3 F 4 ) was detected in the UC spectra other than the weak red emissions ( 1 G 4 → 3 F 4 , 3 F 2,3 → 3 H 6 ). The dominant mechanism for blue emission under 808 nm excitation was attributed to the back energy transfer (BET) Tm 3+ → Yb 3+ and the energy transfer (ET) Yb 3+ → Tm 3+ processes. Upon 808 nm excitation, a two-photon process was deduced from the quadratic dependence of blue UC emission intensity on the fiber laser working current.