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 Y2O3:Yb 3+ /Ho 3+ UCNPs by a self-build swirl flame spray pyrolysis (SFSP) method with a high production rate of ~40 g 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 F4, 5 S2 → 5 I8) and relatively weak red ( 5 F5 → 5 I8) upconversion luminescence (UCL). Based on the UCL spectra of Y2O3: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 Y2O3: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.
Index Terms-Photonic materials, synthesis and fabrication methods, luminiescence and fluorescence, optical properties of photonic materials
I. INTRODUCTIONCNPs refer to the lanthanide-doped nanoparticles that can harvest and convert near-infrared low-energy photons into visible or ultraviolet high-energy photons to realize photon upconversion (UC), which are of broad applications in the fields of three-dimensional display, anticounterfeiting, laser materials, sensors, biological issues, and photovoltaics [1], [2]. Generally, the strategies of synthesizing UCNPs mainly focus on wet chemical routes, including hydrothermal [3]-[5], sol-gel [6]-[8], co-precipitation [9]-[11], thermal decomposition [12]-[14] and ion exchange method [15], [16]. Moreover, some newly emerging methods, such as laser ablation [17], [18], solid state reaction [19]-[22], and electrospinning [23], [24] are also used for fabricating the UCNPs. However, the UCNPs fabricated by these routes are always accompanied by complex chemical processes and harsh experimental conditions. In terms of the traditional wet This paragraph of the first footnote will contain the date on which you submitted your paper for review, which is populated by IEEE.
