Page 59 - Practical book PC406-MNU-2025

MANSOURA NATIONAL UNIVERSIY
PHARM D- CLINICAL PHARMACY LEVEL II INSTRUNENTAL ANALYSIS (PC 406)

 Photoluminescence should involve both photo-excitation and and
emission processes:

1- Photoexcitation process:
It may occur by absorption of one of the following forms of radiant energy:

a- sunlight

b- visible radiation

c- UV

d- X-rays

2- The emission process:

 It is the emission of radiant energy from an excited electronic state.

 Photoluminescence is called fluorescence when the spin of the excited electron

does not change as the photoexcited species undergoes a transition from the

excited state to the ground state.

 The difference in the energy level (∆E) between the excited and unexcited

states during excitation (absorption), fluorescence and phosphorescence are in the

order:

∆E (absorption) > ∆E (fluorescence) > ∆E (phosphorescence)

 As the wavelengths corresponding to the ∆E values are inversely

proportional to the wavelengths, the order of the λ max are:

λ (absorption) < λ (fluorescence) < λ (phosphorescence)

For example, the wavelengths of maximum excitation, fluorescence and

phosphorescence of anthracene are 255nm, 425nm, 680 nm respectively.

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