Novel fabrication, microstructure and upconversion photoluminescence properties of Tm3+, Yb3+co-doped Y2O3translucent ceramics

Article abstract of DOI:10.1016/j.jallcom.2016.07.065

A novel fabrication of Y₂O₃:Tm,Yb translucent ceramics by sintering method using synthetic YF₃:Tm,Yb microtube powders was reported for the first time. The experimental results showed that the full dense microstructure could be obtained with grain size of about 2?μm. The obtained Y₂O₃:Tm,Yb ceramics had less pores and high optical transparency. By using a 980?nm diode laser as the pumping source, the Y₂O₃:Tm,Yb ceramics gave intense blue and red upconversion luminescence emissions, which were ascribed to the radiative transitions of¹G₄→³H_6,¹G₄→³F₄and³F_2,3?→?³H₆of Tm³⁺ions, respectively. The dependence of upconversion emission intensity on the excitation power was examined, and the possible upconversion mechanisms had been proposed accordingly.

Full text of DOI:10.1016/j.jallcom.2016.07.065

Accepted Manuscript
Novel fabrication, microstructure and upconversion photoluminescence properties of
3+
3+
Tm , Yb co-doped Y O translucent ceramics
2 3
Yanyan Guo, Dianyuan Wang, Xinghua Wu, Qingkai Wang, Yong He
PII:
S0925-8388(16)32098-9
10.1016/j.jallcom.2016.07.065
JALCOM 38233
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 21 May 2016
Revised Date: 3 July 2016
Accepted Date: 5 July 2016
Please cite this article as: Y. Guo, D. Wang, X. Wu, Q. Wang, Y. He, Novel fabrication, microstructure
3+
3+
and upconversion photoluminescence properties of Tm , Yb co-doped Y O translucent ceramics,
2 3
Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.07.065.
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Novel fabrication, microstructure and upconversion
photoluminescence properties of Tm3+, Yb3+ co-doped Y2O3
translucent ceramics
Yanyan Guo a, Dianyuan Wang b, Xinghua Wu a,b, Qingkai Wang b, Yong He a,
aFaculty of Materials Science and Chemistry, China University of Geosciences, Wuhan, 430074, China
bCollege of Science, Jiujiang University, Jiujiang 332005, China
ABSTRACT
A novel fabrication of Y2O3:Tm,Yb translucent ceramics by sintering method using
synthetic YF3:Tm,Yb microtube powders was reported for the first time. The experimental
results showed that the full dense microstructure could be obtained with grain size of about
2µm. The obtained Y2O3:Tm,Yb ceramics had less pores and high optical transparency. By
using a 980nm diode laser as the pumping source, the Y2O3:Tm,Yb ceramics gave intense
blue and red upconversion luminescence emissions, which were ascribed to the radiative
1
3
transitions of G4→3H6, 1G4→3F4 and F2,3→3H6 of Tm3+ ions, respectively. The dependence
of upconversion emission intensity on the excitation power was examined, and the possible
upconversion mechanisms had been proposed accordingly.
Keywords: Y2O3:Tm,Yb ceramics; Microstructure; Upconversion; Photoluminescence
Corresponding author. Tel./fax: +86 27 67884286.
E-mail address: yonghe246@126.com (Y. He).

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1. Introduction
In recent years, Rare earth (RE) ion doped near-infrared (NIR) to visible upconversion
(UC) photoluminescence materials possess great potential applications in upconversion lasers,
light emitting display, biological fluorescence labelling, solar cells, and so on [1–8]. It is well
known that UC efficiency is strongly dependent on the host material and doped active ions,
especially the former [9–10], therefore ongoing research mainly focuses on the exploration for
host materials with good thermal stability and low phonon cutoff energy, which makes them
suitable for practical application, and the later one would decrease the possibility of
nanoradiative transitions and in turn result in a high upconversion efficiency. These host
materials that had been developed exist in the forms of crystals, glasses or nanopowders
[11–14]. Although these materials own relatively high upconversion efficiency, the
applications are still greatly restricted due to the poor physical and chemical stability and low
laser-induced damage threshold of the hosts [15–17]. Fortunately, translucent ceramics are
such a kind of materials having both high efficiency and excellent stability. Highly efficient
upconversion emissions had been achieved in RE-doped transparent ceramics, such as CaF2,
YAG, Lu2O3, (Y0.9La0.1)2O3, La2-xGdxZr2O7, which can be fabricated by newly developed
nanosized ceramics powder technology and vacuum sintering method, and have more broad
practical applications than that of the powders [18–22].
Cubic Y2O3 crystal doped with trivalent rare-earth ions has gained much attention as
laser materials due to their superior properties, such as good chemical stability, relatively low
phonon energies (591cm-1), high thermal conductivity (13.6 W/m K) and optical transparency
over a broad spectral range [23]. However, the high melting point (~2430°C) and the

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polymorphic phase from cubic system to a high-temperature hexagonal system at about
2350°C make it difficult to fabricate large Y2O3 crystals of high optical quality by
conventional growth methods. On the other hand, by the conventional ceramic fabrication
technology, it is possible to get optical Y2O3 transparent ceramics at a low sintering
temperature 1600°C–1700°C by vacuum sintering technology [24].
In the previous work, all the Y2O3 ceramics were fabricated by using nanosized Y2O3
powders [25–27]. However, no study has yet been performed by using YF3 micro/nano
powders as ceramics powders. In this work, we successfully fabricated the Y2O3:Tm3+,Yb3+
translucent ceramics by sintering method using synthetic YF3:1%Tm,5%Yb microtube
powders for the first time. The microstructure and UC luminescence properties under 980 nm
laser excitation were investigated in detail, and the possible upconverting mechanisms has
been also proposed through the power dependence of upconverting intensities.
2. Experimental
2.1 Preparation of YF3:Tm,Yb micropowders
YF3:1%Tm,5%Yb micropowders were prepared by a hydrothermal method. Y2O3 (4N),
Tm2O3 (3.5N) and Yb2O3 (4N) were employed as starting raw materials. Firstly, a given
amount of RE2O3 (RE = Y, Tm, Yb) was dissolved in concentrated HNO3 and converted into
RE(NO3)3 solution. Stoichiometric amounts of Y(NO3)3, Tm(NO3)3, Yb(NO3)3 solutions were
mixed, and then NH4F solution was added into the nitrate solution. The pH value was
adjusted to be 10 by adding a small amount of NaOH solution. After being stirred for another
30 min, the mixture was transferred into a 50mL Teflon-lined autoclave, maintained at 180°C

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for 48 h. After being cooled to room temperature naturally, the precipitates were centrifuged
and washed with ethanol and deionized water for several times. Finally, the product was dried
at 80°C for 24 h, and the YF3:Tm,Yb microtube powders were obtained.
2.2 Fabrication of Y2O3:Tm,Yb translucent ceramics
The YOF:Tm,Yb powders were obtained by annealing the as-prepared YF3:Tm,Yb
microtube powders at 700°C for 1 h, and then were uniaxially pressed into pellet with a
pressure of 50MPa. Finally, the pellet was sintered to Y2O3:Tm,Yb translucent ceramics in air
at 1450°C for 20h. The ceramics pellet is about 0.5mm thick.
2.3 Characterization
The crystalline structure was identified using an X-ray diffractometer (SHIMADZU
XD-D1, Rigaku, Japan) with Cu Kα-radiation (λ = 0.15418 nm) in the range of 2θ = 20–80◦.
The morphologies of the powders, the microstructure and EDS spectrum of the as-fabricated
ceramics was studied by a scanning electron microscope (VEGA II LSU, Tescan, Czech
Republic). The transmittance spectrum was recorded on a UV–VIS–NIR spectrophotometer
(UV1901PC, Shanghai Aucy Technology Instrument Co. Ltd, China) in the wavelength range
of 200–1100 nm. The upconversion emission spectra were measured and analyzed by using a
fluorescence spectrometer (F-4500, Hitachi, Japan) under 980nm diode laser (Newport, USA)
excitation at room temperature.
3. Results and Discussion
The XRD patterns of the as-prepared YF3:Tm,Yb microtube powders, the obtained
YOF:Tm,Yb powders and the fabricated Y2O3:Tm,Yb ceramics are presented in Fig. 1. It

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can be found that the patterns of the YF3:Tm,Yb and YOF:Tm,Yb microtube powders
matched well with the YF3 phase (JCPDS 74-0911) and YOF phase (JCPDS 75-0051). The
patterns also exhibited a single cubic Y2O3 phase (JCPDS 25-1200) in this ceramics. The
XRD results reveals that YF3 is oxidized to YOF during the annealing at 700°C, and that YOF
is completely changed to Y2O3 during the sintering process of the ceramics.
The SEM morphology of the as-prepared YF3:Tm,Yb powders was investigated and is
illustrated in Fig. 2. It can be observed that the powder mainly is composed of tube-like
structures with the diameter of 160-200nm and the length of 10-15µm.
Fig. 3 illustrates the transmittance spectrum and photograph of the as-sintered unpolished
Y2O3:1%Tm,5%Yb translucent ceramics. The absorption bands centered at 359nm, 463nm,
1
1
3
3
682nm, 795nm and 950nm correspond to energy level of D2, G4, F2,3, H4 (Tm3+) and
2F5/2(Yb3+), respectively. It can be seen that Y2O3:Tm,Yb ceramics with good optical
properties has been obtained through the sintering YOF:Tm,Yb pellet into Y2O3:Tm,Yb
ceramics. The letters under the ceramics can be seen distinctly.
Detailed microstructures and elemental composition of the as-sintered Y2O3:Tm,Yb
ceramics were further investigated using SEM and EDS. Fig. 4 shows the SEM micrographs
of the surface and fracture plane of the unpolished Y2O3:Tm,Yb ceramics sample. It can be
observed in Fig. 4(a) that there are no cracks or pinholes on the surface of the ceramics pellet.
Fig. 4(b) shows that the full dense microstructure has been obtained with grain size of about
2µm, and there are less micro-pores, and no similar tube-like structures in the ceramics. Fig. 5
shows that the corresponding elemental composition is confirmed by EDS to be Y, O, Tm and
Yb, confirming the presence of Tm and Yb elements is in the Y2O3 ceramics sample. No F

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element is found, it is because that YOF is sintered in air and completely oxidized into Y2O3.
Under relatively weak 980nm diode laser excitation, bright blue upconversion
luminescence from Tm3+, Yb3+ co-doped Y2O3 ceramics can be clearly observed with naked
eyes (Fig. 6(a)). The UC emission spectrum of the Y2O3:1%Tm3+,5%Yb3+ ceramics sample is
shown in Fig. 6. Three UC emission bands centered at 482nm (blue), 652nm and 697nm (red)
1
are obtained, which are ascribed to the radiative transitions of G4→3H6, 1G4→3F4 and
3F2,3→3H6 of Tm3+ ions, respectively.
To get a better understanding of the possible UC mechanisms involved in Y2O3:Tm,Yb
ceramics, the UC emission intensity I was measured as a function of the pumped power P. For
the UC process, I is proportional to the nth power of P, that is: I Pn, where n is the number
of pump photons absorbed per upconverted photon emitted [28]. A plot of lgI versus lgP
yields a straight line with slope n. The values of the slope n for 482nm, 652nm and 697nm
UC emissions are 2.98, 2.97, and 1.91, respectively (Fig. 7), which indicates that these UC
emissions were three-photon and two-photon processes, respectively.
To further recognize the UC mechanisms in the ceramics samples, possible UC processes
are schematically given in the energy level diagrams of Yb3+ and Tm3+ ions as shown in Fig. 8.
The blue and red UC emissions occur via two-step and three-step energy transfer (ET) from
3
3
Yb3+ to Tm3+. First, the Tm3+ ions in the ground state H6 are excited to the state H5 via an
3
ET from neighboring excited Yb3+ ions. Subsequent nonradiative relaxation of H5 populates
3
3
3
the F4 level. In the second-step excitation, Tm3+ ions in the F4 state are excited to the F2,3
via another ET from excited Yb3+ ions. The populated 3F2 may nonradiatively relax to the 3F3
level. The third-step is that Tm3+ ions in the 3F3 level are excited to 1G4 level. Then the 482nm

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(blue), 652nm and 697nm (red) upconversion emissions from 1G4 and 3F2,3 occur [29,30].
4. Conclusion
Y2O3:Tm,Yb translucent ceramics were successfully fabricated by sintering method
using synthetic YF3:Tm,Yb microtube powders for the first time. The microtube-like
YF3:1%Tm3+,5%Yb3+ powders were prepared by the hydrothemal method and used as starting
materials. The microstructure and light transparency of the Y2O3:Tm,Yb ceramics sample
were investigated, and it was found that high optical transparency and full dense
microstructure could be obtained with grain size of about 2µm and less pores. By using a 980
nm diode laser as the pumping source, the upconversion photoluminescence properties of the
Y2O3:Tm,Yb ceramics was studied. The possible upconversion mechanisms had been
proposed accordingly. The as-fabricated Y2O3:Tm,Yb ceramics with high optical transparency,
is promising candidates for upconversion laser materials.
Acknowledgements
The work was supported by the NSFC (Grant No. 51062008, 21463014), Key Project of
Chinese Ministry of Education (Grant No. 212095), Ground Project of Sci & Tech of Jiangxi
(Grant No. KJLD12095).

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Fig. 1. XRD patterns of the as-prepared YF3:Tm,Yb microtube powders, the obtained
YOF:Tm,Yb powders and the fabricated Y2O3:Tm,Yb ceramics
Fig. 2. SEM morphologies of the as-prepared YF3:Tm,Yb powders
Fig. 3. Transmittance spectrum and photograph of the unpolished Y2O3:Tm,Yb ceramics
Fig. 4. SEM micrographs of the surface and fracture plane of the unpolished Y2O3:Tm,Yb
ceramics
Fig. 5. EDS spectrum of the fabricated Y2O3:Tm,Yb ceramics
Fig. 6. Upconversion emission spectrum of the Y2O3:Tm,Yb ceramics under 980nm diode
laser excitation
Fig. 7. The pump power dependence of the upconversion emission intensity of the
Y2O3:Tm,Yb ceramics (under the 980nm excitation)
Fig. 8. The proposed UC mechanisms in Y2O3:Tm,Yb ceramics under 980nm diode laser
excitation

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Highlights
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ꢀ
ꢀ
A novel method of fabricating Y2O3:Tm,Yb ceramics was presented.
The obtained Y2O3:Tm,Yb ceramics had less pores and high optical transparency.
Intense blue and red upconversion emissions were obtained in Y2O3: Tm,Yb
ceramics.