Yb3+在LiLa(WO4)2晶体中的光谱特性及上转换发光研究
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本文主要探讨了Yb<sup>3+</sup>:LiLa(WO<sub>4</sub>)<sub>2</sub>晶体的光谱特性及其荧光动力学。Yb<sup>3+</sup>掺杂的LiLa(WO<sub>4</sub>)<sub>2</sub>是一种备受关注的研究材料，特别是在高功率InGaAs激光器发展的推动下，Yb<sup>3+</sup>因其诸多优势而受到重视。该晶体具有显著的吸收和发射光谱特性，其吸收带宽和发射带宽广泛，这表明它在光转换过程中有高效的能量吸收和释放能力。
Yb<sup>3+</sup>:LiLa(WO<sub>4</sub>)<sub>2</sub>的吸收和发射交叉截面较大，这意味着在特定波长下，晶体能有效地吸收光子并将能量传递给Yb离子。这种特性对于激光技术来说非常重要，因为它可以提升光能量的转化效率。研究发现，在10K的低温环境下，晶体展现出蓝光（约480纳米）的发射，这是通过合作上转换现象实现的，即两个或多个激发态的Yb<sup>3+</sup>离子通过非辐射过程协同释放能量，从而产生更高的能级跃迁并产生可见光。
合作上转换是一个涉及多个离子之间的能量传递过程，它在固态激光器和光放大器中有潜在的应用，特别是在短波长区域，因为单个Yb离子可能无法直接从较高的激发态直接跃迁到较低的发射态。Yb<sup>3+</sup>:LiLa(WO<sub>4</sub>)<sub>2</sub>的这种特性使得它在紫外光到可见光的宽光谱范围内具有潜在的应用价值，例如在光纤通信、生物医学成像和光存储等领域。
此外，文章还提到了光学代码：140.3613，160.5690，300.2140，300.2530，这可能是对研究中的不同光谱区域或特定应用领域的分类编码。这些代码有助于读者快速定位和理解文章在光谱科学中的具体贡献。
总结来说，Yb<sup>3+</sup>:LiLa(WO<sub>4</sub>)<sub>2</sub>晶体的光谱特性研究揭示了其作为高效光转换材料的潜力，尤其是在低温下通过合作上转换实现的蓝光发射，这为未来的激光技术提供了新的研究方向。同时，该晶体的大吸收和发射截面以及适度的荧光寿命使其在多个领域中显示出应用前景。
780 CHINESE OPTICS LETTERS / Vol. 8, No. 8 / August 10, 2010
Spectroscopic characteristics of Yb
3+
:LiLa(WO
4
)
2
crystal
Xinyang Huang (###)
Institute of Research on the Functional Materials, Jiangxi University of Finance and Economy, Nanchang 330013, China
∗
E-mail: xyhuang0202@hotmail.com
Received April 15, 2010
The spectroscopic characterization and fluorescence dynamics of Yb
3+
:LiLa(WO
4
)
2
crystal are investi-
gated. The Yb
3+
:LiLa(WO
4
)
2
crystal exhibits a broad absorption and emission spectral bands, large ab-
sorption and emission cross sections, and moderate fluorescence lifetime. Blue light emission around 480 nm
is observed at 10 K and is demonstrated through cooperative upconversion from the deexcitation of excited
Yb
3+
-Yb
3+
pairs.
OCIS co des: 140.3613, 160.5690, 300.2140, 300.2530.
doi: 10.3788/COL20100808.0780.
Recently, with the development of high-power InGaAs
diode lasers, increasing attention has been paid to the re-
search on Yb
3+
-doped laser materials. This research was
stimulated because Yb
3+
demonstrates many advantages
over other rare earth ions. Yb
3+
only has two electronic
manifolds (i.e., ground-state manifold
2
F
7/2
and excited-
state manifold
2
F
5/2
) separated by approximately 10000
cm
−1
. In addition, Yb
3+
hardly suffers from cross-
relaxation, upconversion, concentration quenching, or
excited-state absorption because it lacks relevant high-
lying excited states. Its quantum efficiency is also very
high, greatly lightening thermal loads, and its long fluo-
rescence lifetime is beneficial for storing energy
[1,2]
. Due
to the presence of strong electron-phonon coupling, Yb
3+
ions have broad absorption and emission bands, offering
the possibility of near-infrared tenability and the gener-
ation of ultrashort pulses
[3−7]
.
Double tungstate crystals with the general formula
AB(WO
4
)
2
(A = Li, Na, or K, B = rare earth) from a
wide variety of inorganic compounds having monoclinic
and tetragonal symmetries have recently attracted grow-
ing interest. Their structure diversity provides these
crystals with excellent physical and chemical properties
as laser hosts, such as excellent chemical durability in air
atmosphere, large rare-earth ion admittance, and large
absorption and emission cross-sections of rare-earth ions
in its lattice
[3−11]
. Yb
3+
-doped double tungstate crystals
with sheelite-type local disorder structure exhibit rela-
tively broad bandwidths, promising to become rare earth
laser hosts for applications requiring tunability or ultra-
short pulses. For example, Yb
3+
laser operation has been
demonstrated in several crystal hosts: NaRe(WO
4
)
2
(Re
= Y, Gd, and Lu
[3−7]
). LiLa(WO
4
)
2
, a Li-based dou-
ble tungstate crystal, possesses no phase transition and
can be directly grown from the flux
[12−14]
. Moreover,
the Yb
3+
:LiLa(WO
4
)
2
crystal exhibits excellent ther-
mal and spectroscopic characteristics
[13,14]
. However,
to our knowledge, the polarized optical characteristics
and upconversion emission of Yb
3+
:LiLa(WO
4
)
2
crys-
tal have not been investigated yet, and this may limit
the study of the Yb
3+
:LiLa(WO
4
)
2
laser. Therefore,
this letter is mainly concerned with the polarized spec-
troscopic characterization and fluorescence dynamics of
Yb
3+
:LiLa(WO
4
)
2
crystal.
The Yb
3+
:LiLa(WO
4
)
2
crystal was grown by the
Czochralski method. The growth procedure was sim-
ilar to those described in Refs. [12,14]. The X-ray
diffraction (XRD) patterns were collected using a
D/max-rA diffractometer and employing CuK
α
radi-
ation (λ = 0.154056 nm) at room temperature. The
Yb
3+
concentration was measured by inductively cou-
pled plasma atomic emission spectrometry (ICP-AES).
The sample, with the dimension of 5 × 5 × 0.5 (mm),
was cut along the [001] orientation from the as-grown
Yb
3+
:LiLa(WO
4
)
2
crystal and polished for spectroscopic
measurement. According to the tetragonal characteristic
of lattices, the experimental spectra were labeled as σ or
π, defined in terms of the E-vector being perpendicular
and parallel to the optical axis c, respectively. Polar-
ized absorption spectra were obtained using a Perkin-
Elmer ultraviolet-visible-near infrared (UV-VIS-NIR)
spectrometer (Lamada-900) in the range of 800 – 1100
nm at room temperature. Emission spectra and fluores-
cence decay curves were recorded on Edinburgh Instru-
ments FLS920 spectrofluorimeter equipped with both
continuous (450 W) and pulsed xenon lamps. For low-
temperature measurements, the sample was mounted on
a closed cycle cryostat (4-350 K, DE202, Advanced Re-
search Systems).
The XRD pattern of as-grown Yb
3+
:LiLa(WO
4
)
2
crys-
tal at room temperature is shown in Fig. 1. The pattern
was analyzed using the Topas 2 program. Results ob-
tained show that the as-grown Yb
3+
:LiLa(WO
4
)
2
crys-
tal belongs to the tetragonal system with space group
I4(1)/a (C
6
4h
) and unit cell parameters: a
0
= 0.5232 nm
and c
0
= 1.1342 nm
[12]
.
Fig. 1. XRD pattern of as-grown Yb
3+
:LiLa(WO
4
)
2
crystal.
1671-7694/2010/080780-04
c
° 2010 Chinese Optics Letters
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