The size-dependent upconversion luminescence properties of β-NaYF4: Yb3+,Ho3+ microprisms

Upconversion for Photovoltaics – a Review of Materials, Devices and Concepts for Performance Enhancement

“…Chen et al reported on the application of β ‐NaYF 4 :25% Yb 3+ ,1% Ho 3+ microprisms to both a standard p–i–n a‐Si and an a‐Si/a‐Si tandem solar cell. For the tandem solar cell, they reported current enhancements that can be converted to an EQE UC of up to 0.007% under laser illumination at 980 nm with 0.5 W cm −2 irradiance, resulting in a normalized EQE UC of 1.4 × 10 −4 cm 2 W −1 .…”

Reducing Grain Size and Enhancing Luminescence of NaYF4:Yb3+, Er3+ Upconversion Materials

“…As is well-known, fluoride-containing host materials are attracting extensive attention over other materials because of their high photochemical stability, low toxicity, high quantum yield, and lower phonon energies which refrain from nonradiative transitions of rare earth ions. − Among fluoride-containing materials, NaYF 4 , as one of the most efficient hosts for upconversion emission, possesses the merits of low phonon energies (<400 cm –1 ), high radiative emission rates, and low nonradiative decay rates, and thus has been widely studied. , It is known that NaYF 4 has two kinds of crystal structures, cubic (α) and hexagonal (β) phases. Generally, the UC luminescence of the materials strongly depends on their structures and morphologies. , Up to now, it is urgent to explore the fundamental relationship of the crystal structure, morphology, grain size, and luminescence of the NaYF 4 materials. , Many investigations have shown that the UC luminescence intensity of the NaYF 4 materials can be effectively controlled through adjusting their morphology. − For example, Li’s group successfully prepared NaYF 4 nanocrystals with tunable shape and size in a water/alcohol/oleic acid system; , Lin et al synthesized β-NaYF 4 microcrystals with diverse morphologies by a hydrothermal method using sodium citrate as surfactant; − and Zhao’s group demonstrated a facile hydrothermal method to synthesize uniform β-NaYF 4 . , However, from the investigations on the NaYF 4 materials, it can be clearly noted that the enhancement in luminescent intensity is generally accompanied by the significant increase of the grain size of the materials, as shown in Figure . − From Figure , the emission intensity of NaYF 4 :Yb 3+ , Er 3+ microcrystals shows a continuous improvement with grain size increasing, suggesting that increasing the size of the β-NaYF 4 : Yb, Er microprisms is a very effective method of maximizing the UC emission efficiency; the UC and DC emission intensities of β-NaYF 4 :Yb, Er nanocrystals synthesized by a solvothermal decomposition approach can be enhanced with increasing particle sizes; the UC emission intensities of β-NaYF 4 :Yb 3+ , Ho 3+ microcrystals are improved with the increase of gain sizes; and the emission intensity of NaYF 4 :Yb,Er nanocrystals increases as particle size increases . It seems that for the NaYF 4 -based materials, the larger the grain size, the stronger the luminescence.…”

“…33,34 However, from the investigations on the NaYF 4 materials, it can be clearly noted that the enhancement in luminescent intensity is generally accompanied by the significant increase of the grain size of the materials, as shown in Figure 1. 35−38 From Figure 1, the emission intensity of NaYF 4 :Yb 3+ , Er 3+ microcrystals shows a continuous improvement with grain size increasing, suggesting that increasing the size of the β-NaYF 4 : Yb, Er microprisms is a very effective method of maximizing the UC emission efficiency; 35 the UC and DC emission intensities of β-NaYF 4 :Yb, Er nanocrystals synthesized by a solvothermal decomposition approach can be enhanced with increasing particle sizes; 36 the UC emission intensities of β-NaYF 4 :Yb 3+ , Ho 3+ microcrystals are improved with the increase of gain sizes; 37 and the emission intensity of NaYF 4 :Yb,Er nanocrystals increases as particle size increases. 38 It seems that for the NaYF 4 -based materials, the larger the grain size, the stronger the luminescence.…”

Photon Upconversion for Photovoltaics and Photocatalysis: A Critical Review

“…For example, Chen et al demonstrated the application of Yb 3+ /Ho 3+ -doped β-NaYF 4 microcrystals to the rear side of a-Si:H/a-Si:H tandem solar cells and observed an additional J sc of 1 μA when illuminating with a 980 nm laser (80 mW cm −2 ). 196 However, a-Si:H tandem devices are still inherently inefficient. Instead, there are also new device structures and architectures being developed that combine, for example, a wide-bandgap metal halide perovskite solar cell on top of a high efficiency c-Si solar cell, exhibiting efficiency exceeding 29%.…”

“…However, other tandem PV devices exist where UC could play a role. For example, Chen et al demonstrated the application of Yb 3+ /Ho 3+ -doped β-NaYF 4 microcrystals to the rear side of a-Si:H/a-Si:H tandem solar cells and observed an additional J sc of 1 μA when illuminating with a 980 nm laser (80 mW cm –2 ) . However, a-Si:H tandem devices are still inherently inefficient.…”