In fluorescence, how do the energies of excitation and emission compare? Which is greater?

• A. Both energies are always zero.
• B. The energy of emission is greater than the energy of excitation.
• C. The energy of excitation is greater than the energy of emission.
• D. The energies of excitation and emission are equal.

Answer: (C)

Verified step by step guidance

1. Understand that fluorescence involves absorption of light (excitation) followed by emission of light at a longer wavelength.
2. Recall that energy of a photon is related to its wavelength by the equation \(E = \frac{hc}{\lambda}\), where \(h\) is Planck's constant, \(c\) is the speed of light, and \(\lambda\) is the wavelength.
3. Since emission occurs at a longer wavelength than excitation, the emitted photon has lower energy because energy is inversely proportional to wavelength.
4. Therefore, the energy of excitation (absorbed photon) is greater than the energy of emission (emitted photon).
5. This difference in energy corresponds to some energy lost as heat or vibrational relaxation before emission occurs.