Lecture 2

Question 1

main ways light is generated?

Answer 1

radiation (heat sources)
radioactivity (gamma rays)
luminescence(sources other than heat)
-photoluminescence: abs of another photon(fluorescence, phosphorescence, most scattering events)
-chemiluminescence: chem rxn
-electroluminescence: electric current
-mechanoluminescence: mech stress

Question 2

main way light is generated?

Answer 2

-electrons are excited to a higher energy level by means of heating for luminescence
-light is generated on discrete levels depending on subs electrons are being excited from
-when electrons drop to normal state, a photon is released

Question 3

fluorescence?

Answer 3

-fluorescent dyes used in biology
-can be described as property of a compound to absorb light in a certain range of wavelengths and emit a different wavelength of light, usually longer (less energy)
-usually a short mean lifetime
-used for immediate applications

Question 4

phosphorescence?

Answer 4

doesnt immediately absorb and re-emit light like fluorescence,it has a transition state that makes light emit at lower energy for longer period of time

Question 5

how does chemiluminescence work?

Answer 5

-emission of light that occurs from chemical rxns that produce high amts of energy lost as photons (These photons are the light)

Question 6

how does bioluminescence work?

Answer 6

-rxns are ATP-driven and relate to luciferin

luciferin + O2 -> (luciferase) oxiluciferin +light

atp is hydrolysed by luciferase enzyme to oxidize luciferin (exciting it) and upon return to ground state a photon is released

Question 7

how can light interact with matter?

Answer 7

reflection, absorption,emission,scattering

Question 8

rayleigh scattering?

Answer 8

elastic (no energy lost) scattering on molcules/objects SMALLER than incident wavelength

Question 9

mie scattering?

Answer 9

elastic (no energy lost) scattering on molecules/objects similar toor larger than incident wavelength

Question 10

raman scattering?

Answer 10

inelastic (energy lost) scattering of photons by matter, meaning that there is both an exchange of energy and change of lights direction (usually scattered photons have lower energy than incident photons)

Question 11

What is the difference
between chemiluminescence,
fluorescence, and
phosphorescence?

Answer 11

Fluorescence and Phosphorescence are based on ability of substance to absorb light and emit light of a longer wavelength and lower energy. The difference between these two is that phosphorescence lingers for a longer period of time.
Chemiluminescence needs activation for chemical reaction (requires ATP in
the bioluminescent case)

Question 12

What is the main
difference between
bioluminescence and thermal
radiation?

Answer 12

Bioluminescence: generated from a source other than heat (ATP-driven chemical reaction)
Thermal Radiation: generated by a heat source

Question 13

What evolutionary pressures
drive bioluminescence?

Answer 13

Two Main Evolutionary Pressures:
1. Survival
a. Counterillumination camouflage, mimicry of other animals, for
example to lure prey or escape predators.
2. Reproduction
a. Signaling to other individuals of the same species to attract mates.

Question 14

What is the photoelectric
effect?

Answer 14

The emission of electrons when electromagnetic radiation, such as light, hits
a material. Electrons emitted in this manner are called photoelectrons.
Photoemission can occur from any material, but it is most common in
metals and other conductors.