Abstract
A new and facile strategy to enhance the upconversion luminescence (UCL) emission of NaLuF4: Er3+ microcrystals (MCs) using strontium (Sr) as a dopant has been reported. With the introduction of Sr2+, the products change from long NaLuF4: Er3+ hexagonal microtubes to short hexagonal microtubes and finally to hexagonal microprisms. The growth mechanism is profoundly discussed according to the different reaction time-dependent morphologies. More importantly, the total fluorescence intensity is significantly reinforced by doping Sr2+ ions. When 18% Sr2+ is doped into NaLuF4: Er3+ hexagonal microtubes, the maximum green and red luminescence intensities are about 5.8 and 4.4 times higher than those of Sr2+-free samples, respectively. The influences of Sr2+ ion doping content on the phase, the morphology, and the local crystal field symmetry of the as-synthesized NaLuF4 crystals are investigated.
Highlights
Upconversion (UC) micro- and nanocrystals refer to a nonlinear optical process in which lower-energy photons are absorbed and higher-energy photons are emitted [1]
As Sr2+ doping concentration rises from 0 to 10%, all the distinct diffraction peaks in the patterns can be labelled as hexagonal phase NaLuF4 (JCPDS 27-0726)
NaLuF4: Er3+ hexagonal microtubes doped with different concentrations of Sr2+ ions have been synthesized via a simple hydrothermal method
Summary
Upconversion (UC) micro- and nanocrystals refer to a nonlinear optical process in which lower-energy photons are absorbed and higher-energy photons are emitted [1]. Lu3+ in NaLuF4 could sensitize the activator and perform volume compensation, resulting in enhanced emission. Despite these advantages, there are still some insurmountable problems. Wang and coworkers studied the effect of Li+ dopant on NaYF4: Yb3+, Er3+ nanocrystals They observed 34-time green and 101-time red emission enhancement and proposed that UC enhancement could be attributed to local crystal field distortion or disrupted local crystal field symmetry around rare-earth ions [24]. Coworkers doped Ca2+ into NaYF4: Nd3+ microcrystal, and the near-infrared luminescence intensity at 1.06 μm increased by about three times [26]. A plausible mechanism for boosting UC luminescence of the synthesized microcrystals is discussed
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