MolDraw › Chemistry tools › UV-Vis Spectrum Viewer
Free UV-Vis Spectrum Viewer
Open UV-Vis spectra, find λmax, work out molar absorptivity or concentration with Beer-Lambert, see the colour of the sample, overlay a whole series and find a band gap with a Tauc plot. Your files stay on your device.
or drop them here. JCAMP-DX (.jdx, .dx) or CSV/TXT (wavelength, absorbance or %T). Pick several files to overlay them.
· Examples are simulated and free to reuse. Download the sample .jdx.
λmax peaks (selected spectrum)
Tap a row to use that λmax in the Beer-Lambert box.
Beer-Lambert: A = ε · l · c
Tauc plot and band gap
Absorbance stands in for the absorption coefficient α, which is fine for finding where the line meets zero. For films or powders, use α or the Kubelka-Munk function for the best numbers.
How to use the UV-Vis spectrum viewer
- Open your file(s), or press an example button.
- Switch between absorbance and %T, and between nm, eV and cm-1.
- Read the λmax table. Tap a row, or tap the plot, to pick the wavelength for Beer-Lambert.
- Enter the path length and concentration to get ε, or ε to get the concentration.
- For a series, open several files and tick Normalise if you want to compare shapes.
- For a semiconductor, open Tauc plot and band gap, choose direct or indirect and read Eg.
- Export a PNG or CSV.
What the numbers mean
λmax is the wavelength where a band absorbs most. Longer conjugated systems absorb at longer λmax. Beer-Lambert says A = ε · l · c, so with A, path length and concentration you get the molar absorptivity ε, or with ε you get the concentration. Keep A below about 1.5 for good numbers.
Colour: a sample that absorbs blue light (435 to 480 nm) looks yellow, because we see the light that is left. The table uses the standard colour wheel. Tauc plot: plot (A·hν)² for a direct gap or (A·hν)^½ for an indirect gap against photon energy, fit the straight edge and read the band gap where the line meets zero.
Frequently asked questions
Is my data uploaded?
No. Files are read and drawn in your browser only.
Which files can I open?
JCAMP-DX (.jdx, .dx) and CSV or TXT with two columns. The x column can be nm, µm, cm-1 or eV and y can be absorbance or transmittance. The tool works out which from the headers or the numbers.
How do I overlay a titration or dilution series?
Pick several files at once, or tick Add to the plot and open more. Each gets its own colour. Tick Normalise to compare band shapes, and tap a name to make it the selected spectrum.
How is the molar absorptivity worked out?
From A = ε · l · c at the λmax or at the wavelength you tap. Enter the path length (usually 1 cm) and the concentration. Enter ε instead to get the concentration.
How does the Tauc band gap work?
The tool turns wavelength into photon energy, plots (A·hν)² for a direct gap or (A·hν)^½ for an indirect gap, finds the steepest straight part of the edge and extends it to zero. You can set the fit range yourself.
Why does my sample look a different colour from the one shown?
The colour comes from the strongest visible band and the colour wheel. Real colour also depends on band width, concentration and the light source, so treat it as a guide.