Low-Temperature Solid-State Synthesis and Upconversion Luminescence Properties in (Na/Li)Bi(MoO):Yb,Er and Color Tuning in (Na/Li)Bi(MoO):Yb,Ho,Ce Phosphors.

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO):Yb,Er [(N/L)BMO:Yb,Er] and (Na/Li)Bi(MoO):Yb,Ho,Ce [(N/L)BMO:Yb,Ho,Ce] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb,Er codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er, H → I) and 551 nm (Er, S → I), in addition to a very weak one at 655 nm (Er, F → I). The (N/L)BMO:Yb,Ho mainly showed a green band around 544 nm (S,F → I) and a red band around 654 nm (F → I) upon 975 nm laser excitation. With increasing Yb concentrations in (N/L)BMO:Yb,0.01Ho, the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb,Er and Yb,Ho were determined to be two-phonons absorption processes in (N/L)BMO:Yb,Er/Ho. The Ce ions were introduced into Yb,Ho codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho (F,S) + Ce (F) → Ho (F) + Ce (F) and (CR2) Ho(I) + Ce (F) → Ho (I) + Ce (F), which is based on the energy matching of CeF-F level pairs with HoI-I and F,S-F level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb, Er and (N/L)BMO:Yb, Ho, Ce materials, and color modulation is easily controlled by varying Yb concentration and a cross relaxation process between Ce and Ho, which provides efficient methods to regulate the emission color of UCL phosphors.