Question 1

What does UV-vis spectroscopy show for iron oxide nanoparticles?

Accepted Answer

Featureless, without a sharp plasmon peak. Hematite (α-Fe2O3) has a strong absorption edge around 550–600 nm and absorbs most of the blue and green, which makes it red, with absorption rising steeply into the UV; magnetite (Fe3O4) absorbs almost evenly across the whole visible and near-infrared (small particles even slightly more at 550 than at 400 nm, tables above), which makes it black. Small particles mostly absorb; above about 100 nm scattering becomes comparable.

Question 2

Magnetite or hematite: what is the difference?

Accepted Answer

Magnetite (Fe3O4) is black and ferrimagnetic, the material of most magnetic nanoparticles (SPIONs, ferrofluids); it often oxidizes to maghemite (γ-Fe2O3), brown. Hematite (α-Fe2O3) is the red, weakly magnetic oxide of rust and red pigments. Choose either in the calculator.

Question 3

What is the refractive index of iron oxide?

Accepted Answer

Magnetite: about 2.3 + 0.1i at 550 nm. Hematite: about 2.9–3.3 with k ≈ 0.4–0.5 at 550 nm (ordinary and extraordinary rays differ). Values from Querry (1985), used by the calculators.

Question 4

Do iron oxide nanoparticles heat under light?

Accepted Answer

Yes. They absorb broadly, including the near-infrared, so laser light heats them (photothermal heating), separately from the magnetic hyperthermia used with alternating magnetic fields. The heating calculator gives the temperature rise for any size and intensity.

Question 5

How do I find the concentration of iron oxide nanoparticles from UV-vis?

Accepted Answer

Measure the absorbance at a fixed wavelength (400 or 550 nm), take the molar extinction coefficient for your size from the tables, and use c = A / (ε ℓ); for other sizes or media the calculator gives Cext and hence ε directly.

Question 6

Can I compute iron oxide nanospheres, core–shell nanoparticles, arrays, near fields, heating or substrates?

Accepted Answer

Yes: both iron oxides can be used for spectra and optical properties of nanospheres and core–shell nanoparticles (add a shell), near-field enhancement maps, nanoparticle arrays and lattice resonances, particles on a substrate and laser heating.

Diameter	ε at 400 nm	ε at 550 nm	Absorbed share at 550 nm
5 nm	1.91 × 10⁵ M⁻¹ cm⁻¹	2.51 × 10⁵ M⁻¹ cm⁻¹	100 %
10 nm	1.55 × 10⁶ M⁻¹ cm⁻¹	2.02 × 10⁶ M⁻¹ cm⁻¹	100 %
20 nm	1.35 × 10⁷ M⁻¹ cm⁻¹	1.66 × 10⁷ M⁻¹ cm⁻¹	99 %
50 nm	4.60 × 10⁸ M⁻¹ cm⁻¹	3.31 × 10⁸ M⁻¹ cm⁻¹	85 %
100 nm	1.69 × 10¹⁰ M⁻¹ cm⁻¹	6.29 × 10⁹ M⁻¹ cm⁻¹	46 %
200 nm	3.23 × 10¹¹ M⁻¹ cm⁻¹	1.89 × 10¹¹ M⁻¹ cm⁻¹	24 %

Diameter	ε at 400 nm	ε at 550 nm	Absorbed share at 550 nm
5 nm	2.95 × 10⁶ M⁻¹ cm⁻¹	6.40 × 10⁵ M⁻¹ cm⁻¹	100 %
10 nm	2.39 × 10⁷ M⁻¹ cm⁻¹	5.16 × 10⁶ M⁻¹ cm⁻¹	100 %
20 nm	2.01 × 10⁸ M⁻¹ cm⁻¹	4.29 × 10⁷ M⁻¹ cm⁻¹	99 %
50 nm	4.45 × 10⁹ M⁻¹ cm⁻¹	9.35 × 10⁸ M⁻¹ cm⁻¹	86 %
100 nm	5.61 × 10¹⁰ M⁻¹ cm⁻¹	2.19 × 10¹⁰ M⁻¹ cm⁻¹	55 %
200 nm	2.45 × 10¹¹ M⁻¹ cm⁻¹	2.96 × 10¹¹ M⁻¹ cm⁻¹	42 %

Iron oxide nanoparticle UV-vis spectrum calculator

Questions & answers

What does UV-vis spectroscopy show for iron oxide nanoparticles?

Magnetite or hematite: what is the difference?

What is the refractive index of iron oxide?

Do iron oxide nanoparticles heat under light?

How do I find the concentration of iron oxide nanoparticles from UV-vis?

Can I compute iron oxide nanospheres, core–shell nanoparticles, arrays, near fields, heating or substrates?

Magnetite (Fe₃O₄) nanoparticles: extinction by size

Hematite (α-Fe₂O₃) nanoparticles: extinction by size

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