A small percentage of cations in an
inert Y2O3 host are replaced by luminescent Eu+3
ions to give a red phosphor. The quality of x-ray diffraction depends on the
particle size and the efficiency of the 4f phosphor transitions is also influenced
by crystallinity of the host. In this experiment measurements are made on the
initial product and on the product after further heating. The study of solid-state
luminescence impacts a wide variety of technologies, including display (CRTs
and flat televisions), lighting (fluorescent lamps and mercury-free lamps),
and medical imaging.
Add 3 mL water, 1.00 g Y(NO3)3.6H2O,
0.06 g Eu(NO3)3.6H2O, and
0.41 g urea to a 30 mL beaker. Because a potentially explosive mixture
is being prepared, add the chemicals to water rather than diluting a mixture
of the solids.
Cover with a watch glass.
Heat the solution in a hood in an oven at 500 degrees C for 10 minutes
(long enough for the reaction to finish and the brown NO2 gas
to disperse).
The heating should be done in a hood in an oven with the door closed.
The movie shows what you would observe if you could see into the oven.
Caution: the brown NO2 gas produced by the reaction is extremely
hazardous to inhale.
The mixture reacts to form a foamy white solid.
Transfer half the product to an alumina crucible.
Heat to 850 degrees C overnight.
Alternate illumination by room light and short-wave ultraviolet light.
The sample on the left has not had the final heat treatment.
Prepare samples for powder diffraction by spreading the powder on double-sided
tape on a glass microscope slide.
Compare the powder diffraction pattern of the product before and after
the last heating step. Increased crystallinity gives narrower diffraction
lines. The reference above explains the method for calculating particle
size based on the data.
Materials
Yttrium(III) nitrate hexahydrate(99.9%), Strem 93-3937 or Aldrich 237957-25G
Europium(III) nitrate hexahydrate (99.9%), Strem 93-6310 or pentahydrate
Aldrich 207918-1G
