Impact of crystal defect on upconverted white-light emission in lanthanide-doped LiNbO3 single crystal

Efficient and stable upconversion white-light is critical for optical applications. Herein, LiNbO3:Ho/Yb/Tm single crystals with different [Li]/[Nb] ratios were grown by Czochralski method. It is found that the crystal structures are not changed with [Li]/[Nb] ratios which varied from 0.946 to 0.991 in the single crystals. The RE ion concentrations are reduced faintly and crystal structures approach perfect with increasing the [Li]/[Nb] ratios. More ideal upconversion white-light is obtained when the [Li]/[Nb] ratio is close to 1. The integrated effects of intrinsic defect concentrations and RE ion concentrations affect the upconversion emission intensity of the single crystal. The lower crystal defect in the bulk single crystal has a positive impact on the enhancement of upconversion emission intensity. In addition, all the CIE coordinates are hardly changed with [Li]/[Nb] ratios and located in the white-light region. The upconversion mechanism analysis indicates the longer lifetimes of intermediate energy levels and the shorter lifetimes of luminous energy levels are beneficial to the upconversion process, and the larger intensity variation of upconversion emission arises from its greater lifetime variations of energy levels. The near-stoichiometric LiNbO3:Ho/Yb/Tm single crystal demonstrates potential applications in stable white-light devices and photoelectric instruments.