Upconversion luminescence properties of NaBi(MoO4)2:Ln3+, Yb3+ (Ln = Er, Ho) nanomaterials synthesized at room temperature

Studies on lanthanide ions doped upconversion nanomaterials are increasing exponentially due to their widespread applications in various fields such as diagnosis, therapy, bio-imaging, anti-counterfeiting, photocatalysis, solar cells and sensors, etc. Here, we are reporting upconversion luminescence properties of NaBi(MoO4)(2):Ln(3+), Yb3+ (Ln = Er, Ho) nanomaterials synthesized at room temperature by simple co-precipitation method. Diffraction and spectroscopic studies revealed that these nanomaterials are effectively doped with Ln(3+) ions in the scheelite lattice. DR UV-vis spectra of these materials exhibit two broad bands in the range of 200-350 nm correspond to MoO42- charge transfer, s-p transition of Bi3+ ions and sharp peaks due to f-f transition of Ln(3+) ions. Upconversion luminescence properties of these nanomaterials are investigated under 980 nm excitation. Doping concentration of Er3+ and Yb3+ ions is optimized to obtain best upconversion photoluminescence in NaBi(MoO4)(2) nanomaterials and is found to be 5, 10 mol % for Er3+, Yb3+, respectively. NaBi(MoO4)(2) nanomaterials co-doped with Er3+, Yb3+ exhibit strong green upconversion luminescence, whereas Ho3+, Yb3+ codoped materials show strong red emission. Power dependent photoluminescence studies demonstrate that emission intensity increases with increasing pump power. Fluorescence intensity ratio (FIR) and population redistribution ability (PRA) of (2) H-11/2 -> I-4(15/2), S-4(3/2) -> I-4(15/2) transitions of Er3+ increases with increasing the Yb3+ concentration. Also, these values increase linearly with increasing the pump power up to 2 W. It reveal that these thermally coupled energy levels are effectively redistributed in co-doped samples due to local heating caused by Yb3+.