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

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:Yb ,Tm and GdOF:Yb,Tm 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:Yb ,Tm) was transformed to the cubic phase of nanospheres (GdOF:Yb,Tm), along with their upconversion color change from blue to red. Broadband upconversion emission was observed from GdOF:Yb,Tm 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.