Crystal growth and spectroscopic properties of Cr
3+
-doped CaGdAlO
4
Zhu Zhang
a,b
, Yisheng Huang
a
, Lizhen Zhang
a
, Shijia Sun
a
, Feifei Yuan
a
, Zhoubin Lin
a,c,
⇑
a
Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
b
Fujian Normal University, Fuzhou 350007, China
c
State Key Laboratory of Structural Chemistry, Fuzhou 350002, China
article info
Article history:
Received 2 December 2016
Received in revised form 26 December 2016
Accepted 30 January 2017
Available online 2 February 2017
Communicated by T.F. Kuech
Keywords:
A1. Characterization
A2. Single crystal growth
A2. Czochralski method
B1. Inorganic compounds
abstract
ACr
3+
:CaGdAlO
4
single crystal with dimensions of £21 33 mm
3
was grown successfully by Czochralski
method for the first time. Its spectral properties including polarized absorption spectra, polarized fluores-
cence spectra, excitation spectrum and fluorescence decay curves were investigated in detail. The absorp-
tion cross-sections at around 573 nm corresponding to the
4
A
2
?
4
T
2
transition of Cr
3+
ions are
4.75 10
20
and 2.56 10
20
cm
2
for
r
- and
p
-polarizations, respectively. The excitation spectrum
shows two broad and intense absorption bands at about 390 nm and 570 nm, which are associated with
the
4
A
2
?
4
T
1
and
4
A
2
?
4
T
2
transitions of Cr
3+
ions, respectively. The emission band with peak at around
744 nm is ascribed to the
2
E ?
4
A
2
transition of Cr
3+
ions, with the emission cross-sections of
5.55 10
22
and 5.41 10
22
cm
2
for
r
- and
p
-polarizations, respectively. The fluorescence lifetime is
4.35 ms at room temperature. The D
q
/B value is 2.72, which means that Cr
3+
ions occupy the lattice sites
with strong crystal field strength. The results show that Cr
3+
:CaGdAlO
4
crystal can be regarded as a
potential laser gain medium.
Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
In recent years, extensive attention has been paid on the tun-
able solid-state laser materials, for they have wide applications
in signal transmission, display devices, information storage, and
so on [1]. Many tunable solid-state laser crystals doped with tran-
sition metal ions such as Ni
2+
,Ti
3+
,Cr
3+
, and Co
2+
have been studied
in detail [2–4], some of them have been commercialized. With the
development of high power laser diode (LD) at present, the solid-
state laser crystals fit for LD pumping attract much more attention.
Cr
3+
ions doped laser materials usually have a strong and broad
absorption band at around 650 nm, which is consistent with the
output wavelength of the commercialized low-cost red AlGaInP
LD. As a transition metal ion, the emission characteristic of Cr
3+
ions is influenced seriously by the around crystal field strength,
it can emit sharp or broad emission bands. In a weak crystal field,
they commonly emit a strong and broad emission in the visible and
near-infrared wavebands, which is needed for tunable materials.
Therefore, Cr
3+
ions doped laser crystals have become one of the
research hot spot [5,6]. So far, the most popular Cr
3+
ions doped
tunable laser materials are Cr
3+
:LiCaAlF
6
,Cr
3+
:LiSrAlF
6
, and Cr
3+
:
BeAl
2
O
4
crystals, etc. [7–9]. All of them have been commercialized.
However, there exist some drawbacks in these crystals, such as the
applications of Cr
3+
:LiCaAlF
6
and Cr
3+
:LiSrAlF
6
crystals are limited
by their mediocre spectral characteristics, poor mechanical and
thermal properties, on the other hand, the growth of these crystals
are difficult; as for Cr
3+
:BeAl
2
O
4
crystal, because beryllium oxide
(BeO) is highly toxic, it also causes great difficulties in the growth
and applications.
Inorganic oxide materials usually have better thermal, mechan-
ical, and optical properties than fluoride materials, and their large
single crystals with good quality are commonly easy to be
obtained, thus they are the ideal candidates for Cr
3+
ions doped
solid-state tunable laser materials. Many Cr
3+
ions doped inorganic
oxide crystals have been grown, like Cr
3+
:BeAl
2
O
4
,Cr
3+
:YAl(BO
3
)
4
,
Cr
3+
:YGG, Cr:GGG, and Cr
3+
:GSGG, and good laser performances
have been achieved in all of them [10–12]. Although some progress
has been made, continuing improvements are required.
CaGdAlO
4
is one member of the family with the formula ABCO
4
,
where A = Ca, Sr, Ba; B = Gd, Y or other rare-earth ions, C = Al, Ga or
other transition metal elements [13]. It belongs to the tetragonal
system with space group I4/mmm, the unit cell parameters are:
a = 3.6586 Å, c = 11.9787 Å, and Z = 4 [14]. CaGdAlO
4
compound
melts congruently, large and high quality CaGdAlO
4
crystal can
be grown using Czochralski technique easily. This crystal has high
mechanical strength (Mohs hardness 6) and high thermal
http://dx.doi.org/10.1016/j.jcrysgro.2017.01.055
0022-0248/Ó 2017 Elsevier B.V. All rights reserved.
⇑
Corresponding author at: Key Laboratory of Optoelectronic Materials Chemistry
and Physics, Fujian Institute of Research on the Structure of Matter, Chinese
Academy of Sciences, Fuzhou 350002, China.
E-mail address: lzb@fjirsm.ac.cn (Z. Lin).
Journal of Crystal Growth 463 (2017) 33–37
Contents lists available at ScienceDirect
Journal of Crystal Growth
journal homepage: www.elsevier.com/locate/crys
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