Yttrium oxide upconverting phosphors. Part 4: Upconversion luminescent emission from thulium-doped yttrium oxide under 632.8-nm light excitation

Article abstract of DOI:10.1021/jp021372s

Strong blue upconversion emission has been observed from Y₂O₃:Tm³⁺ phosphors under 632.8-nm excitation, in addition to weaker green and red emissions. All of these emissions, including the red, showed a two-photon intensity dependence on the incident 632.8-nm laser power. The emissions that showed only a one-photon intensity dependence occurred in the near-IR region of the spectrum. The mechanism for the origins of these emissions was derived from temperature studies over the range of 0 to - 190 ?°C and their dependence on the laser power at room temperature. Energy values are derived for all of the Tm³⁺ levels in the cubic Y₂O₃ lattice between the ³H₆ ground state and the ¹D₂ excited state at ca. 27 500 cm^-1 from the positions of the emission bands.

Full text of DOI:10.1021/jp021372s

1548
J. Phys. Chem. B 2003, 107, 1548-1553
Yttrium Oxide Upconverting Phosphors. Part 4: Upconversion Luminescent Emission from
Thulium-Doped Yttrium Oxide under 632.8-nm Light Excitation
J. Silver,* M. I. Martinez-Rubio, T. G. Ireland, G. R. Fern, and R. Withnall*
Centre for Phosphors and Display Materials, Chemical and Life Sciences, UniVersity of Greenwich,
Chatham Maritime Campus, Chatham, Kent ME4 4TB, United Kingdom
ReceiVed: June 6, 2002; In Final Form: NoVember 19, 2002
Strong blue upconversion emission has been observed from Y2O3:Tm3+ phosphors under 632.8-nm excitation,
in addition to weaker green and red emissions. All of these emissions, including the red, showed a two-
photon intensity dependence on the incident 632.8-nm laser power. The emissions that showed only a one-
photon intensity dependence occurred in the near-IR region of the spectrum. The mechanism for the origins
of these emissions was derived from temperature studies over the range of 0 to -190 °C and their dependence
on the laser power at room temperature. Energy values are derived for all of the Tm3+ levels in the cubic
Y2O3 lattice between the 3H6 ground state and the 1D2 excited state at ca. 27 500 cm-1 from the positions of
the emission bands.
Introduction
We have recently reported studies on cubic Y2O3:Er3+ and
Y2O3:Eu3+ lattices using 632.8-nm laser excitation.1-3 In both
materials, evidence was found for the presence of the dopant
rare-earth element cation on each of the two different lattice
sites. In the cubic Y2O3 lattice, there are two independent M3+
sites, one with C2 symmetry (75% of the M3+ sites) and the
other with S6 symmetry (25% of the M3+ sites), as shown in
Figure 1. In the case of Y2O3:Er3+, the 632.8-nm excitation
directly promotes the Er3+ ion to the F9/2 state, and then the
second photon promotes it to higher-lying levels.1,2 For Y2O3:
Eu3+ under 632.8-nm light excitation, the Eu3+ ion is promoted
to the 5Do level; this is possible only because the 7F2 sublevels
are initially thermally populated, so irradiation with 632.8-nm
light provides sufficient energy to span the Eu3+ 7Fo -5Do
energy gap.3
4
Figure 1. Two Y3+ crystallographic sites in cubic Y2O3.
Experimental Section
Chemical Preparation. The chemicals used in this study are
yttrium oxide (99.99%, Rhone Poulenc, France), thulium(III)
nitrate pentahydrate (99%, Aldrich), urea, and nitric acid (BDH
AnalaR). The urea homogeneous precipitation method7-14 was
used to prepare spherical Y2O3:Tm3+ hydroxycarbonate sub-
micrometer phosphor precursor powders. Yttrium nitrate stock
solution (56.4 g/L) was prepared by dissolving Y2O3 in dilute
nitric acid until the solution reached a pH of 3. Thulium
nitrate (0.02 g) and urea (15.0 g) were dissolved in 500 mL of
the Y(NO3)3 stock solution after it had been diluted 20-fold
with deionized water. The solution was kept boiling on a hot
plate until turbidity was observed, and then it was left for 1 h.
The precipitates were filtered and washed twice with deionized
water.
The precipitates were dried at 60 °C, giving soft, white
powders that were converted to the oxide by firing at 980 °C
in air for 6 h. The final ion concentration ratio, Tm3+:Y3+, was
1:100. All of the powders consisted of Y2O3 in the cubic phase,
as was made evident by X-ray powder diffraction data.1
Characterization of Physical Properties. The morphologies
and the particle sizes of the samples were determined by
scanning electron microscopy (SEM) using a Cambridge Instru-
ments Stereoscan 90 and transmission electron microscopy
(TEM) using a JEOL JEM-200CX. The average diameter of
the spherical particles was estimated to be 300 ( 50 nm from
the measurement of ∼50 particles per SEM picture.
In this work, the possibility of observing upconversion
emission from cubic Y2O3:Tm3+ under 632.8-nm HeNe laser
light excitation is investigated. There have been two previous
studies4,5 on Tm3+-doped materials excited with red laser light,
but in both cases, the materials were codoped. Cs2NaYCl6:
Tm,Mo and Cs2ZrCl6:Tm,Re were excited with light of wave-
lengths in the range of 620-640 nm using a dye laser4 whereas
Tm3+,Er3+ codoped tellurite glasses were pumped at 650 nm
to investigate the upconversion characteristics of Tm3+ and Er3+
luminescences.5 In both of these cases, the assignments of the
emissions are not in agreement with the current assignments.
This is because, in the work reported herein, the component
states of the 3H term have been reassigned so that they increase
3
3
3
in energy in the order H6, H4, and H5, the last two being
reversed in the previous assignments.
In addition, red-to-blue upconversion has also been observed
in Y2SiO5:Tm3+ using tunable red excitation in the 640-690-
nm range.6 However, minimal assignments were undertaken in
this last work, as it was noted that the internal dynamics were
complicated.
* Corresponding authors. E-mail: j.silver@gre.ac.uk, r.withnall@
gre.ac.uk. Fax: 44-208-331-8405.
10.1021/jp021372s CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/28/2003

Yttrium Oxide Upconverting Phosphors
J. Phys. Chem. B, Vol. 107, No. 7, 2003 1549
Figure 2. (a) Anti-Stokes emission spectrum at 25 °C of particles of Y2O3:Tm3+ fired at 980 °C for 6 h. (b) Stokes emission spectrum at 25 °C
of particles of Y2O3:Tm3+ fired at 980 °C for 6 h.
Luminescence and Raman spectra were obtained using a
Labram Raman spectrometer equipped with 1800 and 600
grooves/mm holographic gratings, a holographic supernotch
filter, and a peltier-cooled CCD detector. Samples were excited
at a wavelength of 632.8 nm using a HeNe laser with an output
of 8 mW of power at the sample, unless an attenuation filter
was used. Precise control of the sample temperature ((0.1 °C)
was achieved by means of a Linkam THMS600 temperature-
programmable heating/cooling microscope stage. For cooling,
the THMS stage was used in conjunction with a Linkam LNP
cooling system.
Results and Discussion
All of the Y2O3:Tm3+ samples were shown to have crystal-
lized in the cubic phase from their X-ray diffraction patterns.
TEM and SEM images of typical samples can be seen in Figures
1S and 2S, respectively, of the Supporting Information. From
the examples shown in these Figures, the samples used for this
work can be seen to be made up of hollow spheres. Such hollow
spheres are not uncommon, and we have previously noted
similar ones for Y2O3:Eu3+ 14,15
.
The emission spectrum of cubic Y2O3:Tm3+ at 25 °C is
presented in Figure 2. The electronic energy levels of Y2O3:
Tm3+ in the 0-30 000-cm-1 region are shown in Figure 9 of
Spectral intensities were normalized using the Stokes Raman
band at 375 cm-1 of cubic Y2O3.

1550 J. Phys. Chem. B, Vol. 107, No. 7, 2003
Silver et al.
TABLE 1: Possible Electronic Transitions for Emission
from the Y2O3:Tm3+ Phosphor Absorbing a Maximum of
Two 632.8-nm Photons
transition
wavelength
photon dependence
1D2 f 3H6
1D2 f 3H4
1D2 f 3H5
1D2 f 3F4
1D2 f 3F3
a
450-470 nm
2
2
512-517 nm
not observed
small features possibly
observed (see text)
not observed
2
1D2 f 3F2
1D2 f 1G4
1G4 f 3H6
1G4 f 3H4
1G4 f 3H5
a
475-498 nm
648-687 nm
small features possibly
observed (see text)
not observed
2
2
2
1G4 f 3F4
1G4 f 3F3
1G4 f 3F2
3F2 f 3H6
3F2 f 3H4
3F2 f 3H5
a
a
not observed
1079-1127 nm
not observed
1
1
3F2 f 3F4
3F2 f 3F3
a
a
3F3 f 3H6
3F3 f 3H4
3F3 f 3H5
not observed
Figure 3. Emission bands of Tm3+ in Y2O3 in the 445- to 470-nm
region. The spectra are shown in the order of increasing temperature
from bottom to top: -190, -175, -150, -125, -100, -75, -50, -25,
and 0 °C.
a
a
3F3 f 3F4
3F4 f 3H6
3F4 f 3H4
3F4 f 3H5
a
762-836 nm
a
a
3H5 f 3H6
3H5 f 3H4
3H4 f 3H6
not observed
a
a
a Beyond our detection range.
the 3H6 ground level to a phonon-coupled level of the 3F2 excited
state. The phonon energies of the Y2O3 lattice are in the range
of 0-600 cm-1, where bands due to fundamental vibrations
are observed in the Raman spectrum of this lattice.1-3
1
From the assignments in Table 1, the occupation of the D2
level necessitates a two-photon process that occurs in two steps.
This process involves an energy decay of the Tm3+ ion from
the 3F2 level to a lower level before the absorption of a second
1
photon of 632.8-nm light can promote it to the D2 level (see
the schematic energy-level diagram for Y2O3:Tm3+ in Figure 9
of this article). From the energy-level diagram for Y2O3:Tm3+
1
(see later), it can be seen that the D2-3F4 energy gap of the
Tm3+ ion closely matches the energy of a photon of 632.8-nm
light. Thus, the Tm3+ ion has to decay from the 3F2 level to the
3F4 level before a second photon is absorbed, promoting the
Figure 4. Emission bands of Tm3+ in Y2O3 in the 470- to 505-nm
region. The spectra are shown in the order of increasing temperature
from bottom to top: -190, -175, -150, -125, -100, -75, -50, -25,
and 0 °C.
1
ion to the D2 level.
1
From the D2 level, the Tm3+ ion can decay radiatively via
1
3
the D2 f H4 transition, which gives rise to a strong blue
1
3
emission, or via the D2 f H5 transition, which gives rise to
a weak green emission (see Figure 2a). Radiative decay via the
1D2 f 3H6 transition could also occur, but this would give rise
to an emission in the near-UV region at ca. 28 000 cm-1, which
this article, and all possible transitions between them are listed
and assigned to observed emission features, where observed,
in Table 1. When Y2O3:Tm3+ is excited by 632.8-nm radiation,
the main emission features observed over the range of 400-
1
was not observed. Another decay pathway from the D2 level
3
1
875-nm are due to the following transitions: 1D2 f H4 , D2
f H5 , G4 f H6 , G4 f H4, and F4 f H6 .
1
occurs via relaxation to the G4 level. Subsequent decay from
3
1
3
1
3
3
3
1
3
the G4 level takes place by radiative decays back to the H6
ground level, giving rise to a second strong, blue emission (see
Stark sublevels of the ground and low-lying excited states of
Tm3+ ions on the C2 sites of cubic Y2O3 have been previously
assigned.16 The energy of the 632.8-nm excitation falls outside
the energy range of the 3H6 f 3F2 transition that was previously
reported.16 Because phonon coupling of the lattice to the rare-
earth cations on both extremities of the lanthanide series is
known to be important, it is likely that the absorption of one
photon of the 632.8-nm laser light promoted the Tm3+ ion from
3
Figure 2a), and to the H4 level, giving a strong, red emission
(see Figure 2b). There is no evidence for radiative decay via
1
3
1
3
the D2 f F2 and D2 f F4 transitions, but we cannot rule
out the possibility that weak emission features in the red region
are due to the 1D2 f 3F3 transition (see later). A further strong
emission, not yet mentioned, occurs in the red region, and this
3
3
is assigned to the F4 f H6 transition (see Figure 2b). In

Yttrium Oxide Upconverting Phosphors
J. Phys. Chem. B, Vol. 107, No. 7, 2003 1551
addition, very weak features observed between 1079 and 1127
3
3
nm are assigned to the F2 f H4 transition. The assignments
of the present work are given in Table 1 and Figure 9 of this
article.
The two-photon process explains how the 1D2 and 1G4 levels
are populated. The population of the lower energy levels can
be explained by a one-photon process.
Thus, the anti-Stokes emission from cubic Y2O3:Tm3+ under
632.8-nm excitation involves a decay by ca. 2500 cm-1 of the
3
Tm3+ ion down to the F4 state, after initial excitation to the
3F2 state, before the absorption of a second photon of 632.8-
nm light. This two-photon absorption mechanism, which results
in anti-Stokes emission, is different from those occurring when
cubic Y2O3:Er3+ and cubic Y2O3:Eu3+ are excited by 632.8-
nm light because the Er3+ and Eu3+ ions do not decay from
their initially excited states before the absorption of a second
photon.1-3 This would be reflected in the time evolution of these
signals, which is beyond the scope of the present work.
To make the assignments of the emission bands shown in
Figure 2, the emission spectra were studied over the temperature
range of 0 to -190 °C, and the laser power dependence of the
band intensities was investigated.
Figure 5. Emission bands of Tm3+ in Y2O3 in the 740- to 830-nm
region. The spectra are shown in the order of increasing temperature
from bottom to top: -190, -175, -150, -125, -100, -75, -50, -25,
and 0 °C.
Temperature Dependence of Emission Peaks (0 to -190
°C). In Figure 3, the temperature dependence of the 1D2 f 3H4
transition is shown from 0 to -190 °C. It is apparent that the
three small bands at 446.8, 448, and 450.5 nm (see Figure 3)
that disappear at -190 °C are clearly behaving differently from
the four bands above 451 nm, at 452.1, 452.6, 453.1, and 453.9
nm, which increase in intensity as the temperature is lowered
to -190 °C. The obvious explanation is that the three small
bands are hot bands originating from thermal population of
higher-energy Stark sublevels of the 1D2 state, which has 2J +
1 ) 5 components, and this thermal population decreases as
the temperature drops. All of the other bands in Figure 3 behave
Stokes side, the Raman bands for the Y2O3 lattice have been
discussed previously.1
The bands starting at 648.5 nm and extending to 683 nm (see
Figures 4S and 5S in Supporting Information) show three main
types of temperature behavior between 0 and -190 °C. Those
at 648.7, 649.3, 650.5, 651.2, 652.1, 654.8, 662.8, 663.7, 669.3,
and 673 nm are most intense at 0 °C and least intense at -190
°C except for the last of these bands (673 nm), which also shows
some intensity at -125 °C. The bands at 653.6, 656.2, and
660.6, the five spanning 671 to 672.5, and all of those from
673.6 to 683 nm are maximized at -125 °C. The bands at 661.6
and 665.1 nm are still increasing in intensity as the temperature
is lowered toward -190 °C. The bands are assigned to the 1G4
f 3H4 transition (see Figure 2b). The temperature dependence
of these bands is dependent on the relative populations of the
Stark sublevels of the 1G4 state from where the emissions arise.
The final envelope of emission bands is shown in Figure 5.
Two different temperature dependencies are seen for these
bands. One subset sharpens as the temperature approaches -190
°C whereas the other almost disappears at -190 °C. In Figure
5, it is apparent that all of the features from 765 to 825 nm
sharpen as the temperature decreases, and in several cases, the
intensities of the emission bands are much higher at -190 °C
than at 0 °C. In the 745- to 765-nm region, the opposite behavior
is apparent because the intensities of the bands decrease as the
temperature decreases (particularly that at 750.4 nm). In this
case, the different thermal behavior is due to the fact that there
are two different transitions that give rise to the emission bands
1
identically, in keeping with them all arising from the D2 f
3H4 transition.
The emission bands observed between 474 and 500 nm are
presented in Figure 4. The bands in the range of 475-485 nm
sharpen considerably, and that at 480 nm splits on going down
in temperature, but the other bands in the 485-500-nm range
do not split and show very little sharpening. The only transition
1
that can possibly explain these two groups of bands is the G4
f 3H6 transition. At -190 °C, two of the bands not only have
narrowed but also have split into a number of components. These
are the bands around 480 nm (four bands at -190 °C but only
one band at 0 °C) and that at 483 nm (which is a doublet at
-190 °C and almost a singlet at 0 °C). The most likely
explanation for these observations is a change in the Maxwell-
Boltzmann distribution of populations of the Stark sublevels as
the temperature decreases. There is a small triplet at 515.5 nm
at 0 °C that sharpens to five bands (514.4, 514.6, 515.4, 515.6,
and 516.3 nm) at -190 °C (see Figure 3S of Supporting Infor-
mation). This group of bands has a different temperature de-
pendence than the group of bands between 474 and 500 nm
because the former is still increasing in intensity as the tem-
perature is lowered toward -190 °C whereas the latter has maxi-
mum intensity at -50 °C (see Figure 4). This triplet is assigned
3
3
in this region. The main transition is F4 f H6, and a second
transition accounts for the bands between 745 and 760 nm and
is discussed in Laser Power Dependence (see below).
There was no indication in this study for different temperature
behavior of the Tm3+ ions on the C2 and S6 crystallographic
sites of the cubic Y2O3 lattice; therefore, it is not possible to
identify Stark levels of Tm3+ ions on either site. However, there
is a higher probability that the cations are located on the C2
sites because there are 3 times as many as the S6 sites.
The concentration of Tm3+ ions is 1:100 of the total cations.
Because the phosphor material was prepared by homogeneous
precipitation, it is reasonable to assume that clustering of Tm3+
ions has not occurred. It would therefore be reasonable to expect
1
3
to the D2 f H5 transition. In addition, there is a sixth band
around 513 nm, which is apparent at the lower temperatures
and is also assigned to this transition. Again, the most likely
explanation for these observations is a change in the relative
populations of the Stark sublevels as the temperature decreases.
All of the other features between 517 nm and the laser line
on the anti-Stokes side are anti-Stokes Raman bands.1 On the

1552 J. Phys. Chem. B, Vol. 107, No. 7, 2003
Silver et al.
Figure 8. Power dependence of the blue emission bands in the 470-
to 510-nm region. The spectra are shown in the order of increasing
laser exciting power from bottom to top: 0.08, 0.8, 2, 4, and 8 mW.
The insert shows a logarithmic plot of emission intensity vs laser power
showing a two-photon dependence of this emission.
Figure 6. Power dependence of the near-IR emission bands in the
725- to 855-nm region. The spectra are shown in the order of increasing
laser exciting power from bottom to top: 0.08, 0.8, 2, 4, and 8 mW.
The insert shows a logarithmic plot of emission intensity vs laser power
showing a one-photon dependence of this emission.
Figure 9. Schematic energy-level diagram for Tm3+ ions in cubic Y2O3.
The values of the energies of the levels above the ground state are
derived in this work.
Figure 7. Power dependence of the red emission bands in the 645- to
690-nm region. The spectra are shown in the order of increasing laser
exciting power from bottom to top: 0.08, 0.8, 2, 4, and 8 mW. The
insert shows a logarithmic plot of emission intensity vs laser power
showing a two-photon dependence of this emission.
1
3
both. There is no evidence for the presence of a D2 f F2
transition.
each Tm3+ ion to be separated from its nearest Tm3+ neighbor
by over 8 Å, and hence the Tm3+ concentration is at the single-
ion level.
Laser Power Dependence. Stokes Emission Bands. Figure
6 presents the laser power experimental data for the region 760-
840 nm. The inset, which is a logarithmic plot of laser power
versus emission intensity having a slope of 1.0, shows that most
of these features in this spectral region are due to a one-photon
process. From the energy range of this transition, we assign it
For the emission bands above the Stokes Raman band at 375
cm-1 (648 nm) to 679 nm (see Figure 7), the photon dependence
was determined by plotting the intensity of the peak at 653.5
nm (see the inset of Figure 7, which indicates a two-photon
dependence). Because there is no two-photon dependence of
the 3F4
f f
3H6 transition, the 1D2 3F4 transition can be
eliminated, leaving the 1G4 f 3H4 transition as the only possible
transition to which this band can be assigned.
Anti-Stokes Emission Bands. Figure 8 presents the 470- to
510-nm anti-Stokes region. The inset, which is a logarithmic
plot of laser power versus emission intensity, shows that this
transition is due to a two-photon process. This is consistent with
3
3
to the F4 f H6 transition. As the laser photon has a closer
energy match to the F2-3H6 energy gap, nonradiative decay
3
from the 3F2 to the 3F4 level must then occur. Because no other
bands in the spectra show a one-photon dependence, we can
1
3
1
a G4 f H6 transition. For this transition to occur, the D2 f
1G4 transition must occur first, although this is outside the
detection range of the Raman spectrometer used in this study.
The anti-Stokes emission bands in the 445- to 470-nm region
are given in Figure 7S in Supporting Information. In the inset
to Figure 7S, it is apparent that the slope indicates a two-photon
eliminate the F3-3H6 and the F2-3H6 from occurring under
3
3
red laser excitation.
Figure 6 also shows some very small features in the region
745.5 to 768.6 nm, a small band at 771.0 nm, and a band at
785.9 nm that have a photon dependence greater than 1 (see
Figure 6S in Supporting Information). These bands either arise
1
dependence, and these wavelengths are consistent with a D2
f H4 transition.
1
3
1
3
3
from the D2 f F3 transition or the G4 f H5 transition or

Yttrium Oxide Upconverting Phosphors
J. Phys. Chem. B, Vol. 107, No. 7, 2003 1553
The 1G4 f 3H6 transition is approximately equal in intensity
to the D2 f H4 transition.
There was no observable discrimination between emissions
from Tm3+ ions on C2 and S6 sites of the Y2O3 lattice.
The temperature dependence of the spectra can be largely
explained by the effects of phonon coupling of the lattice to
the rare-earth cations.
1
3
The small features between 1079 and 1127 nm due to the
3
3F2 f H4 transition showed a one-photon dependence.
In Figure 9, we present the overall energy-level diagram for
Y2O3: Tm3+, which shows the transitions giving rise to the
emission bands that we have observed when using 632.8-nm
excitation. The values of the energies of the levels above the
ground state shown in Figure 9 are derived from the spectra
reported in this work. These values do not take account of the
spread of the energies in the 3H6 ground state arising from Stark
split levels and the coupling of lattice phonons to these levels.
However, when considering the values quoted in a previous
Acknowledgment. We express our gratitude to the EPSRC
(grant ref nos. GR/L85176, GR/M78847, and GR/N28535).
Supporting Information Available: TEM and SEM mi-
crographs of particles of Y2O3: Tm3+ after firing at 980 °C in
air for 6 h. Emission bands of Tm3+ in Y2O3 in the 510- to
520-nm, 645- to 660-nm, and 660- to 685-nm regions Power
dependence of near-IR emission in the 740- to 790-nm region.
This information is available free of charge via the Internet at
http://pubs.acs.org.
3
3
report for the H6 f F2 transition16 (which show very good
agreement with our results), the initial excitation by one photon
of 632.8-nm light (15 803 cm-1) would promote the Tm3+ ion
to a level that is no more than one phonon of ∼600 cm-1
References and Notes
3
(1) Silver, J.; Martinez-Rubio, M. I.; Ireland, T. G.; Fern, G. R.;
Withnall, R. J. Phys. Chem. B 2001, 105, 948.
(2) Silver, J.; Martinez-Rubio, M. I.; Ireland, T. G.; Withnall, R., J.
Phys. Chem. B 2001, 105, 7200.
magnitude away from the F2 state. We might well expect the
other transitions to be affected to a similar extent by phonon
coupling of the lattice to the rare-earth cations.
(3) Silver, J.; Martinez-Rubio, M. I.; Ireland, T. G.; Fern, G. R.;
Withnall, R. J. Phys. Chem. B 2001, 105, 9107.
(4) Kirk, A. D.; Furer, N.; Gu¨del, H. U. J. Lumin. 1996, 68, 77.
(5) Tanabe, S.; Suzuki, K.; Soga, N.; Hanada, T. J. Lumin. 1995, 65,
247.
(6) Bielejec, E.; Kisel, E.; Silversmith, A. J. Lumin. 1997, 72-74, 62.
(7) Sordelet, D.; Akinc, M. J. Colloid Interface Sci. 1988, 122, 47.
(8) Milosevic, O.; Jordovic, B.; Uskokovic, D. Mater. Lett. 1994, 19,
165.
(9) Kim, M. J.; Matijevic, E. J. Mater. Res. 1991, 6, 840.
(10) Giesche, H.; Matijevic, E. J. Mater. Res. 1994, 9, 436.
(11) Nishisu, Y.; Kobayashi, M. U.S. Patent 5,413,736, 1995.
(12) Pei, Y.; Liu, X. Chin. J. Lumin. 1996, 17, 5.
Conclusions
It is demonstrated herein that when cubic Y2O3: Tm3+ is
excited by 632.8-nm red laser light the incoming photon effects
a transition to the F2 level of the Tm3+ ion. This excited ion
3
relaxes to the 3F4 level, from where it returns to the 3H6 ground
state producing 762-836-nm emission unless a second incident
632.8-nm photon is absorbed by the excited Tm3+ ion. The
second photon excites the Tm3+ ion to the 1D2 level. From this
level, all of the observed emissions (see Table 1 and Figure 9)
showing a two-photon dependence originate either directly or
indirectly after relaxation to the 1G4 level. Among these, there
are two intense emissions due to the 1D2 f 3H4 and 1G4 f 3H6
transitions in the blue region of the spectrum and, surprisingly,
a red emission due to the 1G4 f 3H4 transition at lower energy
than that of the exciting 632.8-nm photons.
(13) Jiang, Y. D.; Wang, Z. L.; Zhang, F.; Paris, H. G.; Summers, C. J.
J. Mater. Res. 1998, 13, 2950.
(14) Vecht, A.; Gibbons, C.; Davies, D.; Jing, X.; Marsh, P.; Ireland,
T. G.; Silver, J.; Newport, A. J. Vac. Sci. Technol., B 1999, 17, 750.
(15) Jing, X.; Ireland, T. G.; Gibbons, C.; Barber, D. J.; Silver, J.; Vecht,
A.; Fern, G.; Trogwa, P.; Morton, D. J. Electrochem. Soc. 1999, 146, 4564.
(16) Leavitt, R. P.; Gruber, J. B.; Chang, N. C.; Morrison, C. A. J. Chem.
Phys. 1982, 76, 4775.