Broadband Near-Infrared Emission in Er3+–Tm3+ Codoped Chalcohalide Glasses

Article (PDF Available)inOptics Letters 33(20):2293-5 · November 2008with25 Reads
DOI: 10.1364/OL.33.002293 · Source: PubMed
  • 32.04 · Ningbo University
  • 42.85 · Shanghai Institute of Optics and Fine Mechanics, CAS
  • 45.2 · saintyear holding group co.,ltd. china hangzhou
  • 42.41 · Fudan University
Abstract
The near-IR emission spectra of Er3+-Tm3+ codoped 70GeS2-20In2S3-10CsI chalcohalide glasses were studied with an 808 nm laser as an excitation source. A broad emission extending from 1.35 to 1.7 microm with a FWHM of approximately 160 nm was recorded in a 0.1 mol.% Er2S3, 0.5 mol.% Tm2S3 codoped chalcohalide glass. The fluorescence decay curves of glasses were measured by monitoring the emissions of Tm3+ at 1460 nm and Er3+ at 1540 nm, and the lifetimes were obtained from the first-order exponential fit. The luminescence mechanism and the possible energy-transfer processes are discussed with respect to the energy-level diagram of Er3+ and Tm3+ ions.
Broadband near-infrared emission in Er
3+
–Tm
3+
codoped chalcohalide glasses
Yinsheng Xu,
1
Danping Chen,
2,4
Wei Wang,
1
Qiang Zhang,
2,3
Huidan Zeng,
1
Ce Shen,
1
and
Guorong Chen
1,
*
1
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering,
East China University of Science and Technology, Shanghai 200237, China
2
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
3
Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
4
d-chen@mail.siom.ac.cn
*
Corresponding author: grchen@ecust.edu.cn
Received June 3, 2008; revised August 28, 2008; accepted September 1, 2008;
posted September 10, 2008 (Doc. ID 96973); published October 6, 2008
The near-IR emission spectra of Er
3+
–Tm
3+
codoped 70GeS
2
–20In
2
S
3
–10CsI chalcohalide glasses were
studied with an
808 nm laser as an excitation source. A broad emission extending from 1.35 to 1.7
m with
a FWHM of
160 nm was recorded in a 0.1 mol.% Er
2
S
3
, 0.5 mol.% Tm
2
S
3
codoped chalcohalide glass. The
fluorescence decay curves of glasses were measured by monitoring the emissions of
Tm
3+
at 1460 nm and
Er
3+
at 1540 nm, and the lifetimes were obtained from the first-order exponential fit. The luminescence
mechanism and the possible energy-transfer processes are discussed with respect to the energy-level dia-
gram of
Er
3+
and Tm
3+
ions. © 2008 Optical Society of America
OCIS codes: 160.5690, 300.6280
.
The rapid development of the telecommunications in-
dustry and the demand for having additional
amounts of information transmitted over the current
existing fiber-optic networks have stimulated the
need for wider band transmission. In particular, the
application of dense wavelength-division multiplex-
ing (WDM) is growing in popular use. In common ap-
plications of erbium-doped silica-based amplifiers to-
day, the characteristics of the erbium spectra have
constrained the bandwidth of the spectra of the am-
plifiers. To improve this constraint, researchers look
to multiple rare-earth (RE) ions codoping [1,2]. The
Tm
3+
emission (
3
H
4
3
F
4
transition) around
1470 nm allows a band extension in the spectral
range corresponding to the S-band amplifier region,
on the short wavelength side of the conventional Er-
doped fiber amplifier C L bands at 15301570 nm
[2]. However, silica and most silica-based glasses are
not as suitable for Tm-gain devices as they are for Er
ones. This is due to the fact that the transition
Tm
3+
:
3
H
4
3
F
4
suffers appreciable multiphonon de-
excitation because of the relatively high maximum
phonon energy 1100 cm
−1
of these glasses [1,3].
Therefore, the host matrix having low phonon energy
to minimize multiphonon relaxation becomes essen-
tial. Chalcogenide glass is one of the most promising
candidates because of its low phonon energy. More-
over, the addition of halides into sulfide glass dra-
matically improves the radiative properties of RE
ions [4,5].
For this Letter, Er
3+
–Tm
3+
codoped chalcohalide
glasses were prepared, and their broad emissions in
the near-IR region were investigated using the pump
excitation at 808 nm. The possible energy transfer
processes between Er
3+
and Tm
3+
ions are also dis-
cussed.
Glasses were prepared in 6 g batches from high-
purity elements (Ge, In, and S, 5N) and compounds
(CsI, Tm
2
S
3
, and Er
2
S
3
, 3N). The host glass was
70GeS
2
–20In
2
S
3
–10CsI (mol.%), which was chosen
from [6]. Tm and Er of different contents were
codoped as (mol.%): 0.25Tm
2
S
3
-0.05Er
2
S
3
(G1), and
xTm
2
S
3
-0.1Er
2
S
3
[x=0.25 (G2), 0.5 (G3), and 1.0
(G4)] The batches were melted at 950°C in evacuated
10
−5
Pa fused-silica ampules for 12 h and then
quenched in water. The obtained glass samples were
annealed at 300°C for 2 h. Samples with size of 10
10 2mm
3
were well polished to good optical qual-
ity. The absorption spectrum of the sample was per-
formed by a Jasco V-570 spectrophotometer (JASCO
International CO. Ltd., Tokyo, Japan). The near-IR
emission spectra were recorded using a Zolix SBP300
spectrofluorometer (Zolix Corp., Beijing, China) with
InGaAs as detector in 8501700 nm with excitation
of 808 nm laser diode (LD), and the resolution of the
detector is ±1 nm. The fluorescence lifetime measure-
ments were carried out by exciting the samples with
a modulated 808 nm LD. The signals detected by an
InGaAs photodetector in a TRIAX550 spectrofluo-
rometer were recorded using a storage digital oscillo-
scope (Agilent Infiniium 54833D MSO). All optical
measurements were carried out at room tempera-
ture.
The absorption spectrum of 0.1 mol.% Er
2
S
3
and
0.5 mol.% Tm
2
S
3
(G3) codoped chalcohalide glass
sample at room temperature is shown in Fig. 1,
where the corresponding energy levels are marked.
Absorption bands of Er
3+
and Tm
3+
ions are all due to
electron transitions from their ground states
4
I
15/2
and
3
H
6
to the levels specified, respectively, and band
positions are similar to Er
3+
–Tm
3+
codoped fluoride
glasses [7]. The absorption spectra of all the samples
used in this study are similar.
Figure 2 shows the near-IR emission spectra of dif-
ferent Er
3+
–Tm
3+
codoped chalcohalide glasses with
a pump excitation at 808 nm and a pump power of
October 15, 2008 / Vol. 33, No. 20 / OPTICS LETTERS 2293
0146-9592/08/202293-3/$15.00 © 2008 Optical Society of America
200 mW. We see in Fig. 2 that the spectra are domi-
nated by a broad overlapping emission consisting of
the bands from Tm
3+
(1460 nm,
3
H
4
3
F
4
transition)
and Er
3+
(1540 nm,
4
I
11/2
4
I
15/2
transition), thus
covering the specific range between 1.35 and 1.7
m.
Besides, the weak emission bands of the Er
3+
(980 nm,
4
I
11/2
4
I
15/2
transition) and of the Tm
3+
(1230 nm,
3
F
5
3
H
6
transition) were also visible and
not included in Fig. 2. A new strong emission at
1670 nm emerges in the case of the higher Tm
3+
con-
centration (G4), which can be assigned to the short-
wavelength band-edge emission and corresponds to
the electron transition of Tm
3+
from the
3
F
4
multiplet
to the
3
H
6
multiplet [1,8]. Note that the peak emis-
sion for this band is centered at 1840 nm, and its
spectroscopic analysis was limited owing to the upper
limit of the spectrometer at 1700 nm. It is clear from
Fig. 2 that the emissions at 1460 and 1540 nm be-
come stronger with increasing concentration of
Tm
2
S
3
from 0.25 mol.% (G2) to 1.0 mol.% (G4). The
FWHM is 160 nm for 0.1 mol.% Er
2
S
3
and
0.5 mol.% Tm
2
S
3
codoped chalcohalide glass, while
the maximum FWHM is about 200 nm (G2). Such a
bridged broadband emission is scientifically intrigu-
ing and could also be technically important to the
telecommunications community. We attribute it to
the following two positive factors. First, the present
glass system possesses two different coordinate an-
ions S and I that offer more sites for hosting RE ions
effectively. Especially, halide addition exerts positive
effects on emission properties of RE ions [5]. Second,
according to Paulling’s rule of parsimony that the
number of essentially different types of constituent in
a system tends to be small [9], the Er
3+
–Tm
3+
codop-
ing favors the formation of mixed bonds [such as
I–Tm–S, Tm–A A=I,SEr]. Thus the cross relax-
ation of Tm–Tm or Er–Er ions is greatly suppressed
with increasing Er
3+
or Tm
3+
ions owing to a decrease
of transition probability among RE energy levels [10].
To support the above explanations, the fluores-
cence decay curves of all glass samples were mea-
sured by monitoring the emissions of Tm
3+
at
1460 nm and Er
3+
at 1540 nm, respectively, and the
lifetimes were obtained from the first-order exponen-
tial fits. As an example, the fluorescence decay curves
of G3 are shown in Fig. 3, where the inset shows the
lifetime of glass samples as a function of Tm
2
S
3
con-
centration at the same Er
2
S
3
concentration
0.1 mol.%. It is interesting to find that the photolu-
minescence (PL) lifetime of Er
3+
emission gradually
increases with the increasing Tm
3+
concentration,
whereas that of Tm
3+
emission itself decreases. The
similar phenomenon was also observed for samples
G1 and G2; that is, with the increasing Er
2
S
3
concen-
tration from 0.05 to 0.1 mol.% at the constant Tm
2
S
3
0.25 mol.%, the lifetime of Tm
3+
emission increases
from 320 to 470
s at the cost of the lifetime of Er
3+
emission from 1020 to 910
s. This observation
Fig. 1. Absorption spectrum of the G3 glass at room
temperature.
Fig. 2. (Color online) Room-temperature emission spectra
of the Er
3+
–Tm
3+
codoped with different ratio excited at
808 nm.
Fig. 3. (Color online) Fluorescence decay curves of the G3
glass when pumped at 808 nm. It was measured by moni-
toring the emissions of 1460 and 1540 nm at room tem-
perature. The correlation coefficients for the fits by
the first-order exponential decay equation (1460 nm: I
=73.85012exp
t/0.00040
+0.00318; 1540 nm: I = 0.35802
exp
t/0.00111
+0.00433) are 0.9873 for Tm 1460 nm and
0.9878 for Er 1540 nm. The inset is the lifetime of both
emissions as a function of Tm
2
S
3
concentration.
2294 OPTICS LETTERS / Vol. 33, No. 20 / October 15, 2008
strongly supports the above suggestion that RE
codoping suppresses the cross relaxation between
each RE ion.
The near-IR luminescence mechanism for Er
3+
and
Tm
3+
codoped chalcocohalide glasses could be ex-
plained on the basis of the energy-level diagram of
Er
3+
and Tm
3+
ions, as shown in Fig. 4. First, the
808 nm laser excitation of Tm
3+
and Er
3+
populates
the
3
H
4
and
4
I
9/2
levels from the ground states
Tm
3+
:
3
H
6
and Er
3+
:
4
I
15/2
, respectively. The relax-
ation in Tm
3+
from
3
H
4
3
F
4
level yields 1460 nm
emission, whereas the Er
3+
de-excites nonradiatively
to
4
I
11/2
, then to
4
I
13/2
. Finally, Tm
3+
and Er
3+
relax to
the respective ground states
3
H
6
and
4
I
15/2
, generat-
ing the 1840 nm and 1540 nm emissions. There
also exist several shortcuts that make the energy
transfer between Tm
3+
and Er
3+
become possible
[7,8]. The first shortcut is due to a small energy gap
between
3
H
4
of Tm
3+
and
4
F
9/2
of Er
3+
, thus it is
easier to realize a resonant energy transfer to
Er
3+
:
4
I
9/2
level by depopulating Tm
3+
:
3
H
4
level. This
process can explain well the reduction of emission in-
tensity from Tm
3+
at 1460 nm of the sample G2 com-
pared with G1, the quenched emission from Tm
3+
at
1840 nm for samples G1, G2, and G3, and the
higher intensity of Er
3+
emission at 1540 nm of the
sample G3 than that of G2. This process is well con-
sistent with the fact that the lifetime of Er: 1540 nm
increased from G2 940
s to G4 1190
s.Two
other possible energy-transfer processes are related
to the depopulations of Er
3+
:
4
I
11/2
and
4
I
13/2
levels,
respectively, that is, Er
3+
:
4
I
11/2
,Tm
3+
:
3
H
6
Er
3+
:
4
I
15/2
,Tm
3+
:
3
H
5
and Er
3+
:
4
I
13/2
,Tm
3+
:
3
H
6
Er
3+
:
4
I
15/2
,Tm
3+
:
3
F
4
. Both processes consequently
enhance the emission at 1840 nm from Tm
3+
ions in
the case of the sample with the higher Tm
2
S
3
concen-
tration (1.0 mol.%, G4).
In conclusion, broad near-IR emissions were ob-
served when the Er
3+
–Tm
3+
codoped
70GeS
2
20In
2
S
3
10CsI glasses were excited with an
808 nm pump. Especially, a broad emission extend-
ing from 1.35 to 1.7
m with the FWHM of 160 nm
was obtained at room temperature in a 0.1 mol.%
Er
2
S
3
and 0.5 mol.% Tm
2
S
3
codoped bulk glass
sample. PL spectra and PL decay curves indicate that
the Tm
3+
–Er
3+
codoping suppressed the cross relax-
ation between Tm–Tm or Er–Er ions owing to forma-
tion of mixed bonds and therefore a decrease of tran-
sition probability among each RE ion’s energy levels.
The energy-transfer processes between Er
3+
and
Tm
3+
play important roles in the luminescence
mechanism. The results indicate Er
3+
–Tm
3+
codoped
chalcohalide glass can be optimized for an amplified
spontaneous emission source and broadband ampli-
fier applications.
This research is financially supported by the Na-
tional Natural Science Foundation of China (NSFC)
(60578042, 50702021), the Research Funds for Young
Teachers for the Doctoral Program by Ministry of
Education of China (20070251013) and the Shanghai
Leading Academic Discipline Project, project B502.
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Fig. 4. (Color online) Energy-level diagram of Er
3+
and
Tm
3+
ions and the near-IR luminescence mechanisms of
Er
3+
–Tm
3+
codoped chalcohalide glasses with an 808 nm
LD excitation at room temperature. The solid lines stand
for the absorption and emission transitions for Er
3+
and
Tm
3+
ions. The curves stand for energy transfers between
Er
3+
and Tm
3+
ions.
October 15, 2008 / Vol. 33, No. 20 / OPTICS LETTERS 2295
    • "The glass, crystal and rare-earth ions should be considered because the hosts for dopants are cost-effective and easy to produce in large scale, and rareearth materials are abundant in natural source. Rare-earth doped fluoride, fluoro-phosphate glasses123, telluride and fluoro-telluride glasses4567891011, chalcohalide glasses [12,13] and other hosts1415161718 as well as fiber devices1920212223 for mid-infrared luminescence have been reported, and nearly all the literatures concentrated on the single emission at 2.70 μm or other wavelengths. "
    [Show abstract] [Hide abstract] ABSTRACT: This paper reports the simultaneous emissions around 1.53, 1.80, 2.10, 2.70 and 3.00 μm in Er3+-Ho3+ — Nd3+/Tm3+-codoped telluride glasses upon excitation of a conventional 808 nm laser diode. Both emission bands of 1.53 and 2.70 μm were assigned to the transitions of 4I13/2 −4I15/2, 4I11/2 −4I13/2 of Er3+ ions, respectively, the emission near 1.80 mm was assigned to the transition 4F4 −4H6 of Tm3+ ions, and the emissions at 2.10 and 3.00 mm arose from the transitions of 5I7 −5I8, 5I6 −5I7 of Ho3+ ions. The materials are promising for ultra-broad band amplified spontaneous emission optical sources at near and middle infrared region.
    Full-text · Article · Mar 2014
    • "InFig. 3 it is believed that the greater possibility of the cross relaxation, the more enhanced the 1.8 μm emission [17,18]. In this case, the glass matrix with the proper phonon energy plays a crucial role because the phonon energy in glass hosts influences both the pump manifold lifetime, i.e., the Tm 3 H 4 , and the upper laser manifold lifetime, i.e., the Tm 3 F 4 [12]. "
    [Show abstract] [Hide abstract] ABSTRACT: Tm3+ doped GeS2-Ga2S3-CsCI (GGC) chalcohalide glasses are prepared by melt-quenching method. The 1.8 mu m emission of Tm3+ is investigated under the excitation of 808 nm laser diode. The ratio of the 1.8 mu m emission intensity to that of the 1.48 mu m (I-1.8/I-1.48) reaches 10.7, it is much higher than previously reported Tm3+ doped oxide glasses. With the optimized doping concentration, the 1.8 mu m emission in a range of 1756 to 1876 nm shows the largest full-width-at-half-maximum (FWHM) of similar to 120 nm. The life time of Tm3+ reaches millisecond level for the present chalcohalide glasses. It is at the same level as oxide glass counterparts.
    Full-text · Article · Jan 2014
    • "InFig. 3 it is believed that the greater possibility of the cross relaxation, the more enhanced the 1.8 μm emission [17,18]. In this case, the glass matrix with the proper phonon energy plays a crucial role because the phonon energy in glass hosts influences both the pump manifold lifetime, i.e., the Tm 3 H 4 , and the upper laser manifold lifetime, i.e., the Tm 3 F 4 [12]. "
    [Show abstract] [Hide abstract] ABSTRACT: Tm 3+ doped GeS 2 –Ga 2 S 3 –CsCl (GGC) chalcohalide glasses are prepared by melt-quenching method. The 1.8 μm emission of Tm 3+ is investigated under the excitation of 808 nm laser diode. The ratio of the 1.8 μm emission intensity to that of the 1.48 μm (I 1.8 /I 1.48) reaches 10.7, it is much higher than previously reported Tm 3+ doped oxide glasses. With the optimized doping concentration, the 1.8 μm emission in a range of 1756 to 1876 nm shows the largest full-width-at-half-maximum (FWHM) of ~ 120 nm. The life time of Tm 3+ reaches millisecond level for the present chalcohalide glasses. It is at the same level as oxide glass counterparts.
    Full-text · Dataset · Jun 2013 · Journal of Non-Crystalline Solids
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