photoluminescence

Question 1

fingerprint treatments

Answer 1

1930s salts of some lanthanides are fluorescent

1942 complexes of europium, terbium, and samarium luminescence when excited by UV light

long emission lifetime, sharp emission profiles

Lanthanides absorb light with low efficiency

absorbed energy is transferred to the lanthanide which then emits light.

Question 2

gated imaging in 1979

Answer 2

• background fluorescence on the order of a nanosecond
• fingerprint treatment leads to a luminescence lifetime substantially longer than a nanosecond,
• position of the camera defined the gate delay
• fingerprint dusted with a powder terbium complex
  which luminesces with a lifetime on the order of a millisecond.
  -limited in the speed of rotation of the cylinder,
  limits to fingerprint treatments that yield very long lifetimes.
  -eventually the distance between camera and sample becomes too large to get good image resolution.

Question 3

gated imaging mid 1980s

Answer 3

electronically turned on and off very rapidly, in times on the order of 10-8 seconds

Question 4

fluorescent CdSe/ZnS stabilized by octadecaneamine

Answer 4

fingermarks on silicon wafers or paper were immersed in a petroleum ether solution of CdSe/ZnS.

Detailed fluorescent prints were obtained on the silicon wafer specimens but fingermarks were not observed on paper due to heavy background fluorescence under UV illumination.

Question 5

dendrimers

Answer 5

• repetitively branched molecules
• first dendrimers were made by Fritz Vögtle in 1978
• Dendrimers separate and trap the nanoparticles limiting their aggregation size.
• By controlling the chemical structure and size of the dendrimers, different size nanoclusters can be prepared.
• nanoclusters tailored by size to have luminescences ranging from blue to red,
• By tailoring the size of the cluster, the luminescence lifetime is also altered

Question 6

Diimide enhancement

Answer 6

• bonding of lipids (fatty acids) of fingerprint material, to amine functional groups of dendrimers to form the amide linkage does not occur easily.
• diimides convert the carboxylic acid to an ester that more readily reacts with the amine functional group of the dendrimer