Stokes Shift Calculator

Calculator

Input type Wavelengths (nm) Wavenumbers (cm⁻¹) Energies (eV)

Choose what you measured directly.

Absorption peak value

Absorption maximum in the selected unit.

Emission peak value

Emission maximum in the selected unit.

Decimal precision 0 1 2 3 4 5 6 7 8 9 10

Controls displayed rounding in results.

Calculate Calculate Stokes Shift

Quick reference

ν~(cm⁻¹) = 10⁷ / λ(nm)

E(eV) = 1240 / λ(nm)

Typical case: emission shifts to longer wavelength.

• Wavelength Stokes shift: Δλ = λ_em − λ_abs (nm)
• Wavenumber shift: Δν~ = (1/λ_abs − 1/λ_em) × 10⁷ (cm^-1), with λ in nm
• Energy shift: ΔE = E_abs − E_em (eV), where E(eV) = 1240 / λ(nm)

1. Select the input type that matches your measurement.
2. Enter absorption and emission peak maxima values.
3. Choose the desired decimal precision for display.
4. Press calculate to view results above the form.
5. Use download buttons to export CSV or PDF outputs.

1) What Stokes shift represents

Stokes shift is the separation between a material’s absorption maximum and its emission maximum. It captures how far the spectrum relaxes after excitation, usually toward longer wavelengths. Larger shifts generally reduce self-absorption and improve optical separation between excitation and fluorescence detection.

2) Absorption peak versus emission peak

The absorption peak (λ_abs) indicates where the system most strongly absorbs photons, while the emission peak (λ_em) marks where it radiates most efficiently. In typical fluorescence, λ_em > λ_abs. If λ_em is shorter, the behavior is anti-Stokes and often involves thermal or multi-phonon effects.

3) Why units matter in reporting

Wavelength (nm) is practical for filter selection, but wavenumber (cm^-1) aligns with vibrational spectroscopy and is proportional to energy spacing. Energy (eV) connects directly to electronic transitions in dyes, phosphors, and semiconductors. This calculator provides all three for consistent cross-field reporting.

4) Conversions used by the calculator

When you enter wavenumbers, the calculator converts using ν~(cm^-1) = 10⁷/λ(nm). When you enter energies, it uses E(eV) = 1240/λ(nm). After conversion to wavelengths, it computes Δλ = λ_em − λ_abs, Δν~ = (1/λ_abs − 1/λ_em)×10⁷, and ΔE = E_abs − E_em.

5) Typical ranges and quick interpretation

Many organic dyes show shifts of about 10–80 nm depending on solvent and structure, while some quantum dots and polymer fluorophores can show larger values. A 50 nm shift near 500 nm corresponds to a wavenumber shift on the order of ~2000 cm^-1, useful for comparing relaxation strength across samples.

6) Solvent, temperature, and environment effects

Polar solvents can stabilize excited states and increase the shift, while rigid matrices may limit reorganization and reduce it. Temperature can change nonradiative pathways and peak positions. Record solvent type, concentration, and temperature so differences in Δλ or ΔE reflect the sample, not changing conditions.

7) Peak picking and instrument considerations

Peak maxima can move with detector sensitivity, spectral resolution, and baseline correction. Use the same smoothing method and the same bandwidth settings across runs. For asymmetric emission curves, consider fitting a smooth model and extracting the maximum from the fit to reduce noise-driven errors.

8) Practical workflow for reliable comparisons

Measure absorption and emission spectra under consistent geometry, select your input type, and compute shifts in nm, cm^-1, and eV. Export CSV for lab notebooks and PDF for reports. When comparing batches, keep excitation settings constant and document any optical filter changes.

1) What inputs does this calculator accept?

It accepts absorption and emission peaks as wavelengths (nm), wavenumbers (cm^-1), or energies (eV). Select the input type, enter both peak values, and the calculator converts and reports the Stokes shift in all supported units.

2) Why can the wavelength shift be negative?

If the emission peak is at a shorter wavelength than the absorption peak, Δλ becomes negative. This indicates anti-Stokes behavior, which can occur due to thermal population, upconversion, or strong phonon-assisted processes in some systems.

3) Which Stokes shift definition should I report?

Use nm for optics and filter design, cm^-1 for molecular spectroscopy comparisons, and eV for electronic transition discussions. Reporting two units is common when collaborating across disciplines or preparing publications.

4) Does peak broadening affect the result?

Broad spectra make the maximum more sensitive to noise and baseline choice. Use consistent smoothing and, when possible, fit a curve to extract peak positions. Document resolution and processing so shifts remain comparable across datasets.

5) What if I only have one spectrum?

Stokes shift requires both absorption and emission maxima. If you only have emission, estimate absorption from literature or measure it directly. Using unrelated absorption data can misrepresent the true shift for your specific solvent and concentration.

6) How accurate are the conversions?

The calculator uses standard relations ν~ = 10⁷/λ and E = 1240/λ with λ in nm. Accuracy is typically limited by your peak measurement precision and instrument calibration, not by the arithmetic conversions.

7) Can I use this for phosphorescence or delayed emission?

Yes, if you define the emission peak you want to compare. For delayed processes, peaks may shift due to different excited-state pathways. Report the emission type and measurement timing so your shift is interpreted correctly.

Measure peaks carefully, then report shifts with confidence always.