World Journal of Engineering
NANOCRYSYTALS-GLASS COMPOSITES FOR PHOTONIC DEVICES
Shifeng Zhou1, Yu Teng1 and Jianrong Qiu1,2
1
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
2
Institute of Optical Communication Materials, South China University of Technology,
Guangzhou 510640, China
1. Introduction
Nanocrystals-glass
composites
i.e.
glass-ceramics are hybrid materials with
advantages of both relevant crystal and glass.
They have been widely used in various fields. In
this paper, we review our recent research
development on nanocrystals-glass composites
by taking Ni2+-doped glass-ceramics as an
example.
Functional light sources with tunable
wavelength and ultrabroadband characteristics
have been intensely researched in recent years,
due to their diverse range of potential
applications, such as high efficiency solid-state
lighting, biological labeling, and photoelectronic
and photonic devices.[1-4] Novel light sources
emitting in the near-infrared waveband are
especially attractive because cells and tissues
exhibit little auto-fluorescence and transmission
loss of optical signal is low in this region. In fact,
this band has been considered to be the most
important window for biological and optical
telecommunications. Recently, most research
has been focused on isolated emitting-speciesactivated nanoparticles (e.g., with lanthanide
ions) or semiconductor quantum dots for the
development of new infrared luminescent
nano-structure materials. Due to their
impressively plentiful electronic transitions,
lanthanide ions have found important
applications in various types of discrete optical
amplifiers (e.g., Er- or Tm-doped amplifiers).
However, the limited amplification bandwidth of
lanthanide-ion-activated amplifiers (usually less
than 100 nm) cannot meet the demands for mass
information transmission driven by the internet
industry. Although the accumulation of discrete
amplifiers operating at various wave bands may
result in relatively wide amplification
bandwidths, the mechanical combination of
them is not the optimal scheme. An alternative
approach is to develop semiconductor
quantumdot-activated (e.g., by PbS, PbSe, PbTe,
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or HgTe) gain materials by incorporating soluble
nanocrystals into host materials, such as flexible
polymers, in a bottom-up fashion. In this method,
tunable luminescence can be realized by fully
utilizing the quantum confinement effects in the
nanostructured materials. It is also convenient to
fabricate planar active components and even
devices. However, aqueous reprocessing cannot
effectively eliminate the optical loss induced by
hydroxyl species and has difficulty in its
large-scale application, compared with the dry
preparation method. Also, the use of lead-based
materials is seen as unattractive from an
environmental point of view. The development
of new generation tunable and broadband
luminescent nanomaterials continues. One of the
promising approaches is to intentionally
introduce special extra isolated emitting species
(potentially presenting tunable luminescence,
e.g., Mn2+) into less-toxic quantum dots (e.g.,
ZnSe). It is encouraging that the luminescence
peak position in this approach can be controlled
to reach 610 nm. Indeed, it is significant if the
tunable luminescence can be extended to the
near-infrared spectral range.
We reported for the first time the design and
successful fabrication of infrared- luminescent
nanostructured materials with tunable and
ultra-broadband luminescent characteristics by
using only one isolated center—Ni2+. Briefly, the
research is associated with the method of fine
tailoring the local ligand field around the active
center. Ni2+ ions were selected as luminescent
centers after carefully weighing their potential
for tunability. The hallmark of transition metal
(TM) ions is that the electrons in their outmost d
orbital strongly interact with their ligands (i.e.,
neighboring ions or molecules), so that factors
such as the arrangement of surrounding anions
may affect the electronic configuration of the
central active center. In addition, broadband
luminescence with a long lifetime has been
observed in Ni2+-doped nanostructured materials.
World Journal of Engineering
Further research has investigated the origin of
the high performance of Ni2+ in an appropriate
host and shown that the material may be a
promising
infrared
light
source.
The
unprecedented attempt described here involves
utilization of the ‘‘sensitivity’’ characteristics of
TM ions to realize the objective of
ultra-broadband tuning luminescence in a
controlled manner in Ni2+-doped nanostructure
materials.
distances and angles. To test the method, we
fabricated transparent hybrid materials via in situ
precipitation of nanocrystals from glassy
materials. The nano-crystals, which were
predesigned to fit certain requirements such as
having appropriate anion ligands for realizing
luminescence in the desired wave band, acted as
the actual host for active ions. It is exciting that
infrared luminescence can be finely tuned to
cover the whole infrared region, but not have to
be limited to this spectral range. Since these
testing experiments were performed on
transparent hybrid materials and the fabrication
process is based on mature dry-fiber fabrication
technology, a practical application for the
materials can be found in ultra-broadband fiber
amplifiers and tunable fiber lasers. Another
interesting point observed is related to the
surprising effectiveness of the doping; we
suppose that the strong preference of active
center for special coordination—here, octahedral
positions for Ni2+—might be the underling drive
force for doping. The results may potentially
provide a useful reference for the present hot
issue of doping in nanocrystals. In this sense,
further experiments about fabricating doped
nanocrystals by colloidal chemistry methods in
combination with the idea of local ligand field
design may help to fabricate various types of
new-generation
Cd(Pb)-free
functional
luminescent
nanocrystals.
Wide
applications—from
wavelength-tunable
micro-emitters
to
bio-imaging—can
be
anticipated.
2. Results and Discussion
A thorough knowledge of the distribution
characteristics of various energy levels is of key
importance in controlling the electron transitions
between them. According to the Tanabe- Sugano
diagram of octahedral Ni2+, a decrease in the
crystal field strength (Dq) may result in a
reduction of the transition energy from the
excited state levels to the ground state level.
Furthermore, the theoretical prediction suggests
that Dq is inversely proportional to the fifth
power of the inter-nuclear distance between the
TM central ion and the surrounding ligand. The
electron transition characteristics of the central
ions can potentially be tuned via control of the
nature of the metal-ligand interactions.
Guided by the theoretical prediction, two
different local environments of GaO6 and BaO6
octahedron are employed, since they show
notable differences, including the inter-nuclear
distance of Ga-O and Ba-O bonds and the local
arrangement. To solve the problem of supporting
nanometer-sized crystals, which is particularly
important in nanotechnology and, especially, for
photonic applications, in situ precipitation of
nanocrystals from glassy materials is attempted.
Two novel types of highly transparent hybrid
materials
embedded
with
Ni2+-doped
nanocrystals are fabricated successfully and, as
expected, the goal of wavelength-tunable and
ultra-broadband
luminescence
are
simultaneously realized.
4. References
[1] T. Kuykendall, P. Ulrich, S. Aloni, P. D.
Yang, Nat. Mater. 2007, 6, 951.
[2] Y.Nakayama, P. J. Pauzauskie, A. Radenovic,
R. M. Onorato, R. J. Saykally, J. Liphardt, P.
D. Yang, Nature 2007, 447, 1098.
[3] I. L. Medintz, H. T. Uyeda, E. R. Goldman,
H. Mattoussi, Nat. Mater. 2005, 4, 435.
[4] X. Michalet, F. F. Pinaud, L. A. Bentolila, J.
M. Tsay, S. Doose, J. J. Li, G. Sundaresan, A.
M. Wu, S. S. Gambhir, S. Weiss, Science
2005, 307, 538.
3. Conclusions
We present an effective way to design
wavelengthtunable and ultra-broadband infrared
light sources via tailoring of the ligand
properties, including coordination, TM–anions
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