Fine-tuning of multiple upconversion emissions by controlling the crystal phase and morphology between GdF3:Yb3+,Tm3+ and GdOF:Yb3+,Tm3+ nanocrystals

Abstract

Fine-tuning of multi-color emission characteristics of upconversion lanthanide-ion-doped nanocrystals is of high importance for 3-D color displays, multi-color bio-imaging, and multiplexed cellular labeling. Here, we report a strategy enabling crystal phase transition and morphology transformation between GdF₃:Yb³⁺,Tm³⁺ and GdOF:Yb³⁺,Tm³⁺ nanocrystals for fine-tuning of upconversion multi-color emissions. By controlling the ratio between oleylamine (OM)/octadecene (ODE), the orthorhombic phase of rhombic nanoplates (GdF₃:Yb³⁺,Tm³⁺) was transformed to the cubic phase of nanospheres (GdOF:Yb³⁺,Tm³⁺), along with their upconversion color change from blue to red. Broadband upconversion emission was observed from GdOF:Yb³⁺,Tm³⁺ nanocrystals at a high excitation power, which is expected to originate from oxygen defects. Multi-color upconversion nanocrystals providing broadband emission are expected to find their applications in broad band multi-color biomolecular imaging requiring a high imaging resolution.