Atomistic evolution during the phase transition on a metastable single NaYF4:Yb,Er upconversion nanoparticle

Min Wook Pin,Yong Il Kim,Suji Choi,Chang Hoon Jeon,Eun Jin Park,Tai Hwan Ha,Young Heon Kim

doi:10.1038/s41598-018-20702-9

Abstract

The phase evolution of as-prepared NaYF4:Yb,Er upconversion nanoparticles (UCNPs) with a metastable cubic structure is studied based on in situ heating experiments via transmission electron microscopy (TEM). The atomistic behavior on the single NaYF4:Yb,Er UCNP is observed during the phase transition. The formation and evolution of voids on the NaYF4:Yb,Er UCNP appear at a temperature below 420 °C. Small circular voids are transformed at the initial stage to a large, hexagonal-pillar shaped single void. Two different routes to reach the stable α-phase from the metastable cubic structure are identified on a single NaYF4:Yb,Er UCNP. The first is via a stable β-phase and the second is a direct change via a liquid-like phase. The specific orientation relationships, [110]cubic//[11bar{2}0]hexagonal and {002}cubic//{2bar{2}00}hexagonal, between the cubic and hexagonal structures are confirmed. Additionally, a few extra-half planes terminated in the cubic structures are also observed at the cubic/hexagonal interface.

Highlights

NIR-to-UV/visible upconverting nanoparticles (UCNPs) have attracted much attention in biomedical applications, e.g. bioimaging, biosensors, and near infrared (NIR)-initiated drug delivery systems (DDSs)
Because the α-phase NaYF4:Yb,Er upconversion nanoparticles (UCNPs) are considered a metastable phase at a room temperature, a detailed study on the thermal stability and the phase evolution of the UCNPs is required for more precise applications[24]
We studied the phase evolution of NaYF4:Yb,Er UCNPs as a function of temperature

Summary

OPEN Atomistic evolution during the phase transition on a metastable

Received: 20 September 2017 Accepted: 23 January 2018 Published: xx xx xxxx single NaYF4:Yb,Er upconversion nanoparticle. The phase evolution of as-prepared NaYF4:Yb,Er upconversion nanoparticles (UCNPs) with a metastable cubic structure is studied based on in situ heating experiments via transmission electron microscopy (TEM). Successful syntheses of NaYF4:Yb,Er nanocrystals with β- and α-phases have recently been reported based on various solution methods, e.g. modified precipitation, hydrothermal methods, and non-hydrolytic approaches In these methods, size and shape were controlled by adjusting the growth conditions[9,10,11,12,13,14,15,16,17,18,19,20]. The phase transition from β-phase to α-phase NaYF4:Yb,Er UCNPs, and as-prepared cubic structure to β-phase, was induced by heating experiments with X-ray diffraction analyses[21,22,23]. In situ heating experiments in TEM were systematically conducted to study the thermal stability and phase evolution of the as-prepared materials. Single crystalline NaYF4:Yb, Er nanoparticle image recorded at the electron-beam current density of 2.906 A/cm[2]

Result and Discussion

Conclusion

Author Contributions

Additional Information