Aerosol Flame Synthesis and Manipulating Upconversion Luminescence of Ultrasmall Y2O3:Yb3+/Ho3+ Nanoparticles

The synthesis of upconversion nanoparticles (UCNPs) by flame aerosol is of great significance to realize industrial large-scale production of UCNPs and develop nanotechnology further. Here, for the first time, we successfully fabricated the ultrasmall Y
₂
O
₃
:Yb
³⁺
/Ho
³⁺
UCNPs by a self-build swirl flame spray pyrolysis (SFSP) method with a high production rate of ∼40 g
$ \cdot $
h
⁻¹
. These flame-made UCNPs are all pure cubic phases with an average ultrasmall size of ∼14 nm. Excited by 980 nm laser, the synthesized UCNPs show bright green (
²
F
₄
,
⁵
S
₂
→
⁵
I
₈
) and relatively weak red (
⁵
F
₅
→
⁵
I
₈
) upconversion luminescence (UCL). Based on the UCL spectra of Y
₂
O
₃
:Yb
³⁺
/Ho
³⁺
UCNPs, the optimal doping concentrations of 6 mol% Yb
³⁺
and 0.1 mol% Ho
³⁺
were determined to reach the most intense UCL. The dependence of UCL intensity and pump power was further analyzed, and it indicated that the green and red UCL are two-photon processes. In addition, the UCL properties with different synthesized conditions were also demonstrated. The UCL mechanism of these flame-made Y
₂
O
₃
:Yb
³⁺
/Ho
³⁺
UCNPs were illustrated in detail. Our results prove that industrial large-scale production of continuous one-step synthesis of UCNPs by flame aerosol technology is completely feasible and deserves further study.