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Sweet Briar College Honors Summer Research Program
A Study of YVO4
Submitted by Caville Stanbury
Faculty Advisor Hank Yochum
The properties of two samples of YVO4 were studied in order to better understand the differences between
the samples’. Sample 1. was noticeably more yellow than sample 2. although both samples were grown
under similar conditions. The experiments performed were absorption, photoluminescence and decay time
spectra. These experiments were done for each sample. The absorption spectrum of both samples was
noticed as having a shoulder between 375nm and 475nm. The emission spectrum produced by sample 1
peaked at wavelength of 470nm while that of sample 2 peaked at a wavelength of 475nm. The decay time
of sample 1. was shorter than that of sample2.
Introduction
The study of optical materials is pertinent to modern technology. The work done here
represents a preliminary study of YVO4. Yttrium Orthovanadate (YVO4) crystal is a
commercially grown crystal. Commercially grown crystals are grown in chunks or
boules. The most popular method of growth is the Czochralski technique. YVO4 is
effective in many applications because of its birefringence and thermal properties.
Birefringence of a crystal is the splitting of a light wave into two unequally reflected or
transmitted waves by a crystal. The birefringence is dependent on the wavelength of the
incident light. The split waves take different paths. This property is useful in
telecommunications applications such as multiplexing. Other applications that use this
property of crystals are fiber optic isolators, beam displacers and optical combiners.
YVO4 is also a promising laser host material. When some materials are
introduced/pumped with ions they give off energy in the form of light. This property of
some crystals makes them very useful in laser devices. For example the very popular
Nd:YAG laser is produced by pumping the YAG crystal with neodymium. YVO4 may
replace the popular YAG crystal in diode pumped lasers used in scientific, medical and
military applications. When compared to the YAG crystal, YVO4 is found to be
potentially more efficient.
However when YVO4 is grown, defects are often observed in the boule. For our research
we set out to study the properties of two crystal samples. One sample (sample 1.) was
noticeably more yellow than the other (sample 2). The properties we studied were
photoluminescence, optical absorbance and decay time. Studying these properties can
give information about the possible differences in the atomic structure of both samples. It
can also tell how these differences affect the various applications in which the crystal is
used.
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Experimental and Results2
Absorbance
Poly Scientific Division of Northrop Grumman grew the crystals used in these
experiments by the Czochralski technique. A ultra-violet visible spectrophotometer was
used to obtain the absorption spectra of both samples. A graphical representation was
produced of the degree of absorbance of each wavelength, which entered the crystal. The
decay time for sample 1. was 34s and for sample 2. was 43s
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
350
Sample 1
Sample 2
370
390
410
430
450
470
490
Wavelength (nm)
Graph 1.
As shown in Graph 1. both samples have an absorbance shoulder between 375nm –
475nm. However, the absorbance of sample 1. at the shoulder was noticeably more than
that of the sample 2. This increase in absorbance can be attributed to oxygen vacancy in
the atomic structure of sample 2. Oxygen vacancy is a lack of oxygen ions in the
structure of the crystal. This lack of oxygen ions could also be responsible for the more
yellowed appearance of sample 1.
The samples were both excited at 337nm and their fluorescence spectra taken. The
fluorescence spectrum is a graphical representation of the wavelengths produced or
emitted and shows the intensity of each. This excitation wavelength was chosen because
shown in Graph 1. both samples absorbed light of this wavelength significantly. Both
samples emitted light of various wavelengths. As shown in Graph 2, the emission
spectrum produced by sample 1 peaked at wavelength of 470nm while that of sample 2
peaked at a wavelength of 475nm. The emission of both samples was bluish in colour.
The fluorescence spectrum obtained for the sample 1. also showed a shift towards the
larger wavelength. Sample 1. absorbed more of the shorter wavelengths and less of the
longer wavelengths than sample 2.
2
Sample 1.
0.8
Intensity
0.6
Sample2.
0.4
0.2
0
-0.2350
400
450
500
550
600
650
700
-0.4
Wavelength (nm)
Graph 2.
The differences noted in samples’ emission spectra suggest differences in crystal
impurities and/or structure. The YVO4 has zircon tetragonal crystal structure. Our
findings suggest that the structure of our defected sample has a deficiency of oxygen
ions. Previous researches done on YVO4 agree with this hypothesis. While other works
suggest that the emission observed from sample 1. is related to the transition of VO3-4
ions. We are however unable to conclusively attribute the difference in emission to
oxygen vacancies.
For each sample, the decay time of specific emitted wavelengths was taken. Across each
band the decay times were found to be within 3s of each other. That is, for every
wavelength of each sample the decay time was found to be similar. However, the average
decay times for the samples were different. The decay time for sample 1. was 34s and
for sample 2. was 43s.
ln(Intensity)
Comparison Of Natural Log of Intensity
Decay for Coloured and Uncoloured
Sample
0
-0.5 0
-1
-1.5
-2
-2.5
-3
-3.5
20
40
60
80
100
Time (s)
Graph 3.
Graph 3. shows a linear representation of the average decay time for both samples at
their peak wavelengths from their respective fluorescence spectrum.
Sample 1.
This difference in decay times also suggests that there is a difference in the samples’
structures.
Sample 2.
Future Direction
We wish to conduct experiments over a wider range of absorption strengths at the
shoulder. We intend to verify our current results by studying the photoluminescence and
decay time spectra at the observed shoulders of our new samples.
References
Applied Physics Letters, Volume 80 number 7, Anti-Stokes emission in undoped YVO4,
Ryba Romanowski et al, 2002.
Optics Letters, Volume 19, number 16, Decoloration of yttrium orthovanadate laser host
crystals by annealing, Y. Nobe et al, 1994.
YVO4 crystals – puzzles and challenges, W. Ryba Romanowski, 2003
Luminescent Materials. G. Blasse, B.C. Grabmaier, Springer- Verlag, 1994