# Upconversion nanoparticles: two infrared photons in, one visible photon out

> Lanthanide upconversion written as a sum: two near-infrared photons absorbed by ytterbium ions in a NaYF₄ core are relayed to erbium, which emits one visible photon. Under the sum, the energy ladder, how a shell lifts quantum yields from fractions of a percent towards 13%, and uses written as small equations: hidden inks, 28 nm nanoscopy and zebrafish embryos.

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- Updated: 2026-10-14
- Category: Graphical abstracts
- Method: Graphical abstract
- Starting materials: NaYF₄ nanocrystals doped with Yb³⁺ (sensitizer) and Er³⁺ (activator), grown inside a shell
- Product: Nanoparticles that turn 980 nm near-infrared light into visible green and red light
- Key result: QY 0.005–0.3% (10–100 nm) vs 3% bulk (Boyer & van Veggel 2010); up to 13% core–ultrathick shell (Liu & Jiang 2026); 28 nm STED resolution (Liu et al. 2017)
- Figure: 1920 × 1080 px, 111 editable layers

## Steps

1. **Two photons in**: Yb³⁺ ions absorb near-infrared light (980 nm excitation) and pass the energy to Er³⁺ in two transfers (Jung et al. 2015)
2. **One photon out**: Er³⁺ emits in two green bands and one red band; the red mostly via ⁴I₁₁/₂ → ⁴I₁₃/₂ → ⁴F₉/₂ (Jung et al. 2015)
3. **A shell keeps the light**: Bare 10–100 nm particles: 0.005–0.3% quantum yield, bulk 3% (Boyer & van Veggel 2010); a core in an ultrathick shell: up to 13% (Liu & Jiang 2026)
4. **Uses**: Inks read under 980 nm (Xu et al. 2019), STED nanoscopy at 28 nm (Liu et al. 2017), particles in zebrafish embryos with minimal toxicity (Mirmajidi et al. 2024); little autofluorescence background (Liu & Chen 2026)

## Uses

- Graphical abstracts on lanthanide upconversion
- Talks on near-infrared-excited probes and anti-Stokes emission
- Teaching sensitizer–activator energy transfer

## References

1. Jung et al., “The preferred upconversion pathway for the red emission of lanthanide-doped upconverting nanoparticles, NaYF4:Yb3+,Er3+”, Phys. Chem. Chem. Phys. 2015. https://doi.org/10.1039/c5cp01634g (primary)
2. Boyer & van Veggel, “Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles”, Nanoscale 2010. https://doi.org/10.1039/c0nr00253d (primary)
3. Liu & Jiang, “Brightening Upconversion Nanoparticles”, Acc. Chem. Res. 2026. https://doi.org/10.1021/acs.accounts.5c00910 (review)
4. Liu & Chen, “Photophysics-Guided Upconversion Nanosystems for Sensing”, Acc. Chem. Res. 2026. https://doi.org/10.1021/acs.accounts.5c00916 (review)
5. Liu et al., “Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy”, Nature 2017. https://doi.org/10.1038/nature21366 (primary)
6. Xu et al., “Dual-Mode, Color-Tunable, Lanthanide-Doped Core-Shell Nanoarchitectures for Anti-Counterfeiting Inks and Latent Fingerprint Recognition”, ACS Appl. Mater. Interfaces 2019. https://doi.org/10.1021/acsami.9b10989 (primary)
7. Mirmajidi et al., “Nano-bio interactions of Gum Arabic-stabilized lanthanide-based upconverting nanoparticles: in vitro and in vivo study”, J. Mater. Chem. B 2024. https://doi.org/10.1039/d4tb01579g (primary)
8. Wang et al., “Tuning upconversion through energy migration in core-shell nanoparticles”, Nat. Mater. 2011. https://doi.org/10.1038/nmat3149 (further reading)

Credit: Drawn by LabCanvas after Jung et al., Phys. Chem. Chem. Phys. 2015 (doi:10.1039/c5cp01634g); Boyer & van Veggel, Nanoscale 2010 (doi:10.1039/c0nr00253d); Liu & Jiang, Acc. Chem. Res. 2026 (doi:10.1021/acs.accounts.5c00910); Liu et al., Nature 2017 (doi:10.1038/nature21366); Xu et al., ACS Appl. Mater. Interfaces 2019 (doi:10.1021/acsami.9b10989); Mirmajidi et al., J. Mater. Chem. B 2024 (doi:10.1039/d4tb01579g).

## Questions

**What does the “Upconversion nanoparticles: two infrared photons in, one visible photon out” template show?** Lanthanide upconversion written as a sum: two near-infrared photons absorbed by ytterbium ions in a NaYF₄ core are relayed to erbium, which emits one visible photon. Under the sum, the energy ladder, how a shell lifts quantum yields from fractions of a percent towards 13%, and uses written as small equations: hidden inks, 28 nm nanoscopy and zebrafish embryos.

**What are the steps shown in “Upconversion nanoparticles: two infrared photons in, one visible photon out”?** 1. Two photons in: Yb³⁺ ions absorb near-infrared light (980 nm excitation) and pass the energy to Er³⁺ in two transfers (Jung et al. 2015). 2. One photon out: Er³⁺ emits in two green bands and one red band; the red mostly via ⁴I₁₁/₂ → ⁴I₁₃/₂ → ⁴F₉/₂ (Jung et al. 2015). 3. A shell keeps the light: Bare 10–100 nm particles: 0.005–0.3% quantum yield, bulk 3% (Boyer & van Veggel 2010); a core in an ultrathick shell: up to 13% (Liu & Jiang 2026). 4. Uses: Inks read under 980 nm (Xu et al. 2019), STED nanoscopy at 28 nm (Liu et al. 2017), particles in zebrafish embryos with minimal toxicity (Mirmajidi et al. 2024); little autofluorescence background (Liu & Chen 2026).

**What are the starting materials and the product?** Starting materials: NaYF₄ nanocrystals doped with Yb³⁺ (sensitizer) and Er³⁺ (activator), grown inside a shell. Product: Nanoparticles that turn 980 nm near-infrared light into visible green and red light.

**Which papers is “Upconversion nanoparticles: two infrared photons in, one visible photon out” based on?** Jung et al., “The preferred upconversion pathway for the red emission of lanthanide-doped upconverting nanoparticles, NaYF4:Yb3+,Er3+”, Phys. Chem. Chem. Phys. 2015 (doi:10.1039/c5cp01634g); Boyer & van Veggel, “Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles”, Nanoscale 2010 (doi:10.1039/c0nr00253d); Liu & Jiang, “Brightening Upconversion Nanoparticles”, Acc. Chem. Res. 2026 (doi:10.1021/acs.accounts.5c00910); Liu & Chen, “Photophysics-Guided Upconversion Nanosystems for Sensing”, Acc. Chem. Res. 2026 (doi:10.1021/acs.accounts.5c00916); Liu et al., “Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy”, Nature 2017 (doi:10.1038/nature21366); Xu et al., “Dual-Mode, Color-Tunable, Lanthanide-Doped Core-Shell Nanoarchitectures for Anti-Counterfeiting Inks and Latent Fingerprint Recognition”, ACS Appl. Mater. Interfaces 2019 (doi:10.1021/acsami.9b10989); Mirmajidi et al., “Nano-bio interactions of Gum Arabic-stabilized lanthanide-based upconverting nanoparticles: in vitro and in vivo study”, J. Mater. Chem. B 2024 (doi:10.1039/d4tb01579g); Wang et al., “Tuning upconversion through energy migration in core-shell nanoparticles”, Nat. Mater. 2011 (doi:10.1038/nmat3149).

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