Stokes Shift Calculator
The Stokes shift between absorption and emission maxima in nm, cm⁻¹ and eV.
Stokes shift Δλ
40.00 nm
Stokes shift Δν̃
1602.6 cm⁻¹
= 4.804e+4 GHz
Energy difference ΔE
0.1987 eV
= 198.7 meV
Quote the shift in cm⁻¹ or eV: the same Δλ means a larger energy gap in the blue than in the red. The widths only shape the chart; the bands are drawn as Gaussians in wavelength for illustration.
Absorption and emission bands
- Absorption
- Emission
- Shift between the maxima
Δλ = λ_em − λ_abs
Δν̃ = 10⁷ (1/λ_abs − 1/λ_em) cm⁻¹ (λ in nm)
ΔE = hc (1/λ_abs − 1/λ_em), hc = 1239.84 eV·nm
The Stokes shift is the gap between the absorption and emission maxima. After excitation the molecule relaxes vibrationally, and its surroundings reorganise, before it emits, so emission comes from a lower energy. Solvent polarity adds to the shift (Lippert–Mataga). Compare maxima taken on the same axis: a band's maximum moves when a spectrum per nm is converted to one per cm⁻¹. The vibronic model on the band-model page shows how the shift follows from the Huang–Rhys factor.
Model and references
Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers
Exact conversion between the two maxima (vacuum wavelengths). The band shapes in the chart are Gaussians in wavelength, for illustration only.
- Lakowicz J. R. (2006). Principles of Fluorescence Spectroscopy, 3rd ed., ch. 1. Springer.