Abstract
In this study, the upconversion (UC) emissions of Er3+ and Yb3+ co-doped SrZrO3 nanocrystals (NCs) were investigated in terms of the thermal annealing temperature and concentration of Er3+ ions and compared with the emissions under a near-ultraviolet (near-UV) excitation. The NCs were synthesized by the combustion method, and the as-synthesized NCs were post-annealed at high temperatures. The X-ray diffraction patterns revealed that the grain sizes and crystallinity degrees of the samples increased with increasing annealing temperatures. The photoluminescence spectra of our samples exhibited strong green and very weak red emissions with the near-UV excitation, originating from the f-f transitions in the Er3+ ions. Interestingly, under near-infrared (near-IR) excitation, we identified sizable visible emissions at 525, 547, and 660 nm in our NCs, which indicated that the UC process successfully occurred in our NCs. These UC emissions were maximized in the NCs with an Er3+ concentration of 0.02 and thermal annealing at 1000 °C. We found that the intensity ratios of red to green emissions increased with increasing annealing temperatures. We discussed the differences in the emissions between near-UV and near-IR excitations.
Highlights
Upconversion (UC) phosphors have attracted considerable attention from researchers because of their various possible applications, such as flat panel display, solidstate laser, and bioimaging
We investigated the emission properties of Er3+ and Yb3+ ion doped SZO NCs synthesized by the combustion method with post-thermal annealing under near-UV
The X-ray diffraction (XRD) patterns revealed that with increasing annealing temperature, the grain sizes and crystallinity degrees of the NCs increased for all Er3+ concentrations
Summary
Upconversion (UC) phosphors have attracted considerable attention from researchers because of their various possible applications, such as flat panel display, solidstate laser, and bioimaging. UC is a nonlinear antiStokes optical process, where two or more photons are sequentially absorbed and light at a shorter wavelength than the excitation wavelength is emitted [1,2]. As a representative RE element for the UC process, Er3+ has been known to show green and red UC emissions [3,4,5,6]. To improve the UC intensity of Er3+, Yb3+ ions, with a large absorption cross section at around 980 nm, have been used as sensitizers [9,10]. Various phosphors combining the UC properties of Er3+ and Yb3+ ions have been intensively studied [11,12,13,14,15]
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