Stimulated Emission Flashcards
What is fluorescence in the context of electronic emission spectroscopy?
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation, where the emitted light usually has a longer wavelength than the absorbed light, and it occurs without a change in electron spin.
Define phosphorescence and how it differs from fluorescence.
Phosphorescence, unlike fluorescence, involves a change in electron spin and occurs over a longer time scale. It is the emission of light that continues after the excitation source has been removed.
What is a Jablonski diagram?
A Jablonski diagram is a graphical representation of the electronic states of a molecule and the transitions between these states, including absorption, fluorescence, and phosphorescence.
Explain the concept of quantum yield in fluorescence.
Quantum yield in fluorescence is the ratio of the number of photons emitted to the number of photons absorbed, indicating the efficiency of the fluorescence process.
What is stimulated emission, and why is it significant in laser technology?
Stimulated emission is the process by which an incoming photon induces a molecule in an excited state to drop to a lower energy state, releasing a second photon. It is fundamental in laser operation because it leads to the amplification of light.
How does the fluorescence process occur at the molecular level according to the Jablonski diagram?
In fluorescence, an electron absorbs energy and is excited to a higher energy state. It may lose some energy non-radiatively through vibration and then returns to the ground state, emitting a photon with less energy than the absorbed one.
Describe the steps involved in phosphorescence according to the Jablonski diagram.
In phosphorescence, an electron absorbs energy and moves to a higher energy singlet state, undergoes intersystem crossing to a triplet state (change in spin), and then returns to the ground state over a longer period, emitting light.
What are the typical time scales for fluorescence and phosphorescence?
Fluorescence typically occurs within nanoseconds (10^-7 to 10^-9 seconds), while phosphorescence can last from microseconds to several seconds (10^-6 to 1 second).
What factors influence the efficiency of phosphorescence in materials?
The efficiency of phosphorescence is influenced by the presence of heavy atoms which facilitate intersystem crossing, the depth of electron traps in the material, and the temperature which affects the release rate of energy from the traps.
How is the color of the emitted light from a fluorescent material determined?
The color of the emitted light depends on the energy difference between the absorbed photon and the emitted photon, which is determined by the molecular structure of the fluorescent material.
Discuss how the molecular environment affects the quantum yield of fluorescence.
The quantum yield of fluorescence can be affected by factors such as solvent interactions, molecular conformation, and the presence of quenching species which can non-radiatively dissipate the energy absorbed by the molecule.
Consider the applications of phosphorescent materials in technology. What are some practical uses?
Phosphorescent materials are used in emergency signs, glow-in-the-dark products, and other applications where light is needed for an extended period after the energy source is removed.
How does the presence of an optical cavity enhance the process of stimulated emission in lasers?
An optical cavity in a laser setup enhances stimulated emission by reflecting photons back and forth through the gain medium, promoting further stimulated emissions and leading to the amplification of coherent light.
Explore the potential impacts of adjusting the laser’s gain medium composition on its output.
Adjusting the gain medium can change the wavelength, efficiency, and power of the laser output. Different materials and dopants can tailor the laser for specific applications, from medical use to telecommunications.
What challenges exist in measuring the quantum yield of fluorescent substances, and how can they be overcome?
Challenges in measuring quantum yield include ensuring accurate calibration of the spectroscopic equipment, choosing appropriate standards for comparison, and controlling environmental factors that can affect fluorescence. These can be overcome by using rigorous experimental protocols and advanced equipment.
