Correct option is A
Explanation-
Option A - Non-radiative loss of excitation energy
This phenomenon is known as the Stokes shift. When a fluorophore absorbs light (excitation), some of the absorbed energy is lost through non-radiative processes (like vibrational relaxation) before the molecule emits light (emission). As a result, the emitted light has less energy and therefore a longer wavelength than the absorbed (excitation) light.
Incorrect options-
Option B - Partial absorbance of incident light
Partial absorbance refers to how much of the incoming light is absorbed, but it does not explain the shift in wavelength between excitation and emission. It affects intensity, not wavelength.
Option C - Scattering of light by molecules
Scattering affects the direction and possibly the intensity of light but not the wavelength difference between excitation and emission.
Option D - Radiative loss of excitation energy
Radiative processes involve emission of photons (light), not energy loss. The energy lost before emission (causing the red-shift) is non-radiative, not radiative.
So, the correct answer is Option A -Non-radiative loss of excitation energy
This is the correct explanation for the Stokes shift, where some energy is lost through non-radiative processes before emission, causing a longer emission wavelength.
