Morphology/dimensionality induced tunable upconversion luminescence of BiOCl:Yb3+/Er3+ nano/microcrystals: intense single-band red emission and underlying mechanisms

Abstract

Preparation of lanthanide (Ln³⁺)-doped upconversion (UC) materials with controlled morphology/dimensionality is desired to fulfill the requirements of different applications. In this work, a series of BiOCl:Yb³⁺/Er³⁺ nano/microcrystals with multiform morphologies, such as 1D nanorods (NRs), 2D nanoplates (NPs), and 3D hierarchical architectures (HAs), were successfully synthesized via a facile solvothermal method by altering the Bi source and reaction solvent. Furthermore, the dependences of UC luminescence performance on morphology/dimensionality have been discussed in detail and compared with each other. The results show that with increasing dimensionality from 1D to 3D, the UC luminescence intensities of red emission are enhanced 4-fold , and the red-to-green (R/G) ratio is increased from 2.5 to 85.4. The energy-back-transfer [⁴S_3/2 (Er³⁺) + ²F_7/2 (Yb³⁺) → ⁴I_13/2 (Er³⁺) + ²F_5/2 (Yb³⁺)] processes and the non-radiative relaxation [⁴I_11/2 (Er³⁺) → ⁴I_13/2 (Er³⁺)] rate are found to be responsible for the morphology/dimensionality dependent UC luminescence properties, confirmed by rate equation modeling. The above results may be helpful for design and fabrication of high performance BiOCl:Yb³⁺/Er³⁺ UC materials, and the 3D HA BiOCl:Yb³⁺/Er³⁺ nano/microcrystals may have a promising application in biological imaging.