Explain the differences between PL and PLE measurements; Explain why the PLE experiment can provide information about the absorption features of a semiconductor! Explain why PL spectrum is typically much narrower than absorption spectrum; Explain why we say optical transitions are \"vertical\". Solution the PL measurements are based on fixed energy excitation.and detection energy is varied.PLE is just reverse process we have detection energy fixed and excitation energy varied. PLE spectroscopy is a useful method to investigate the electronic level structure of materials with low absorption due to the superior signal-to-noise ratio of the method compared to absorption measurements. PL spectroscopy is a contactless, nondestructive method of probing the electronic structure of materials. Light is directed onto a sample, where it is absorbed and imparts excess energy into the material in a process calledphoto-excitation. One way this excess energy can be dissipated by the sample is through the emission of light, orluminescence. In the case of photo-excitation, this luminescence is calledphotoluminescence or PL. As fluorophores play the central role in fluorescence spectroscopy and imaging we will start with an investigation of their manifold interactions with light. Afluorophore is a component that causes a molecule to absorb energy of a specific wavelength and then re-remit energy at a different but equally specific wavelength. The amount and wavelength of the emitted energy depend on both the fluorophore and the chemical environment of the fluorophore. Fluorophores are also denoted as chromophores, historically speaking the part or moiety of a molecule responsible for its color. In addition, the denotation chromophore implies that the molecule absorbs light while fluorophore means that the molecule, likewise,emits light. The umbrella term used in light emission is luminescence, whereas fluorescence denotes allowed transitions with a lifetime in the nanosecond range from higher to lower excited singlet states of molecule.thats why narrower..

1. Explain the differences between PL and PLE measurements; Explain why the PLE experiment
can provide information about the absorption features of a semiconductor! Explain why PL
spectrum is typically much narrower than absorption spectrum; Explain why we say optical
transitions are "vertical".
Solution
the PL measurements are based on fixed energy excitation.and detection energy is varied.PLE is
just reverse process we have detection energy fixed and excitation energy varied.
PLE spectroscopy is a useful method to investigate the electronic level structure of materials
with low absorption due to the superior signal-to-noise ratio of the method compared to
absorption measurements.
PL spectroscopy is a contactless, nondestructive method of probing the electronic structure of
materials. Light is directed onto a sample, where it is absorbed and imparts excess energy into
the material in a process calledphoto-excitation. One way this excess energy can be dissipated by
the sample is through the emission of light, orluminescence. In the case of photo-excitation, this
luminescence is calledphotoluminescence or PL.
As fluorophores play the central role in fluorescence spectroscopy and imaging we will start with
an investigation of their manifold interactions with light. Afluorophore is a component that
causes a molecule to absorb energy of a specific wavelength and then re-remit energy at a
different but equally specific wavelength. The amount and wavelength of the emitted energy
depend on both the fluorophore and the chemical environment of the fluorophore. Fluorophores
are also denoted as chromophores, historically speaking the part or moiety of a molecule
responsible for its color. In addition, the denotation chromophore implies that the molecule
absorbs light while fluorophore means that the molecule, likewise,emits light. The umbrella term
used in light emission is luminescence, whereas fluorescence denotes allowed transitions with a
lifetime in the nanosecond range from higher to lower excited singlet states of molecule.thats
why narrower.