Colored glasses

Question 1

Where are there mechanisms for absorption in standard commercial glasses?

Answer 1

~ in the IR and UV

~ NOT in the visible part of the electromagnetic spectrum

Question 2

What happens if transition metals are added to the glass?

Answer 2

~ absorption of light in the visible spectrum IS possible

Question 3

Why are transition metals added to the glass?

Answer 3

~ they have INCOMPLETELY FILLED D ORBITALS

~ 4s level lower energy than 3d, fills first so 3d subshell is partially empty with 10 states

Question 4

What are ligands?

Answer 4

~ neighboring oxygen anions in a glass network

Question 5

What is special about the coordination of transition metals?

Answer 5

~ either tetrahedrally (GLASS FORMER) or octahedrally (NETWORK MODIFIER) coordinated with negatively charged oxygen anions

~ for example, octahedrally coordinated d-orbitals with electron lobes close to ligands shift UP in energy

~ the splitting of previously degenerate states is the reverse for tetrahedral coordination

~ this difference can result in absorption of light in the visible part of the spectrum! via excitation of a d-level electron into the higher energy state

Question 6

What is Δ of the color center altered by?

Answer 6

1. bond angle
2. field from the 2nd nearest neighbor
3. oxidation state of the transition metal

Question 7

Where does absorption occur?

Answer 7

~ over a wide range of wavelengths, which therefore sets a color by the remaining wavelength range still transmitting

Question 8

What is the extinction coefficient?

Answer 8

~ the absorption coefficient divided by the concentration of absorbing ion

Question 9

What are ruby glasses?

Answer 9

~ Au (0.01-0.02wt%)

~ introduced into a lead-silicate via solution in nitric/hydrochloric acid

~ the melt is quenched to a colorless glass

~ upon reheating to above Tg, Au ions agglomerate into neutral Au colloidal precipitates, which function as Rayleigh scattering centers –> red color

Question 10

What is the reheating process in ruby glasses referred to as?

Answer 10

~ “striking a ruby”