Bathochromic shift

Bathochromic shift (from Greek βαθύς bathys, "deep" and Greek χρῶμα chrōma, "color") is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency). Because the red color in the visible spectrum has a longer wavelength than most other colors, this effect is also commonly called a red shift.