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| RESEARCH ACTIVITIES |
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| Zeolites-based Visible and Near-infrared Emitting Materials |
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P61. Zhenhua Bai, Minoru Fujii1, Yuki Mori, Yuji Miwa, Minoru Mizuhata, Hong-Tao Sun, and Shinji Hayashi1,
"Efficient near-infrared luminescence and energy transfer in Nd-Bi codoped zeolites ,”
Materials Research Socienty Symposium Proceeding, Vol. 1342, pp. 61-66 (2011).
(Proceedings of Materials Research Society 2011 spring meeting,
San Fransisco, USA, - (2011)) |
| We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange
process and subsequent high-temperature annealing. The emission covers
the range of 970∼1450 nm, corresponding to the electronic transitions of
Nd3+ ions and Bi-related active centers (BiRAC), respectively. The introduction
of Bi distinctly broadens the excitation band of Nd3+ in the visible region,
and the lifetime of Nd3+ reaches as long as 354 μs. In the zeolite matrix,
Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as
a sensitizer of Nd3+ ions, and the latter one act as a blockage to avoid
the quenching effect of coordinated water, which enable Nd3+ ions to show
efficient near-infrared (NIR) emission even the zeolites contain large
amount of coordinated water. The excellent optical and structural properties
make these NIR emitting nanoparticles promising in application as laser
materials and biological probes. |
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156. Zhenhua Bai, Minoru Fujii, Takashi Hasegawa, Shohei Kitanoa, Kenji Imakita, Minoru Mizuhatab, and Shinji Hayashi,
Co-existence of Bi with multiple valence states in zeolites-controlling the optical properties by annealing atmosphere
Optical Materials, Vol. 34 , pp. 821-825 (2011).
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| We investigate the effect of annealing atmosphere on the optical
properties of Bi doped zeolites by diffuse reflectance, steady state and
time-resolved photoluminescence (PL), and PL excitation measurements. The
results reveal that zeolites can be used as an excellent host material
to stabilize multiple Bi centers (Bi3+, Bi2+, and Bi-related near-infrared
(NIR) active centers) in the framework, which shows ultra-broadband emission
from visible to NIR range. Annealing in N2 leads to the partial conversion
of Bi3+ ions into Bi2+ and Bi-related NIR active centers. Our results demonstrate
that the broadband NIR emission may be attributed to the electronic transition
of Bi low valence state, rather than a higher valence state. |
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153. Zhenhua Bai, Minoru Fujii, Takashi Hasegawa, Kenji Imakita,Minoru Mizuhata and Shinji Hayashi,
Efficient ultraviolet-blue to near-infrared downconversion in Bi-Dy-Yb doped zeolites
Journal of Physics D: Applied Physics, Vol. 44, pp. 455301 1-5 (2011).
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| Ultraviolet-blue to near-infrared (NIR) downconversion is investigated
for the Dy3+–Yb3+ couple in zeolites by steady-state and time-resolved
photoluminescence (PL) spectra, and PL excitation spectra. Upon excitation
of the 4F9/2 level of Dy3+, NIR quantum cutting could occur through a two-step
energy transfer from one Dy3+ ion to two neighbouring Yb3+ ions via an
intermediate level. The energy transfer efficiency from the 4F9/2 level
is estimated to be 42%, and the intrinsic PL quantum efficiency of Yb3+
emission reaches 54%. The findings may have potential application in enhancing
the energy efficiency of silicon-based solar cells. |
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147. Zhenhua Bai, Minoru Fujii, Takashi Hasegawa, Kenji Imakita, Yuji Miwa,
Minoru Mizuhata, and Shinji Hayashi
Effect of doping concentration on broadband
near-infrared emission of Bi doped zeolites
Microporous and
Mesoporous Materials, Vol. 145, pp. 21-25 (2011). |
![[ABSTRACT]](logo312.gif) A series of Bi doped zeolites are prepared by an ion-exchange process
by changing doping concentration in a wide range, and the optical properties
are investigated. The near-infrared photoluminescence (PL) intensity, full
width at half maximum and decay time depend strongly on Bi doping concentration.
The PL intensity increases 178 times when the concentration is changed
from 0.3 to 1.5 at. %. At the same time, the lifetime increases from 83
to 527 μs. The results prove the model that doped Bi acts not only as optically
active centers, but also as pore-sealing substances to isolate the centers.
The comparison of PL and Raman data suggests that in addition to previously
proposed Bi2O3, other Bi-related materials, probably Bi metal, play an important role to isolate the active centers. |
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145. Zhenhua Bai, Hong-Tao Sun, Minoru Fujii, Yuji Miwa,Takashi Hasegawa, Minoru
Mizuhata and Shinji Hayashi,
Bismuth-sensitized Efficient Near-infrared
Luminescence from Ytterbium in Zeolites
Journal of Physics D:
Applied Physics, Vol. 44, 155101, pp. 1-5 (2011). |
| Yb–Bi co-doped zeolites are prepared by a method consisting of a
simple ion-exchange process and subsequent high-temperature annealing.
We observe two strong near-infrared (NIR) emission bands overlapping in
the range 930–1480 nm, corresponding to the electronic transitions of bismuth-related
active centres (BiRAC) and Yb3+ ions, respectively. In the obtained products,
the excitation wavelength of Yb3+ is extended to the range 420–850 nm,
and the lifetime reaches 665 µs. In the zeolite matrix, Bi ions exist as
BiRAC and Bi compound agglomerates. The former act as a sensitizer of Yb3+
ions, and the latter act as a blockage to seal the pores of zeolites, which
enables Yb3+ ions to show efficient NIR emission even if the zeolites contain
a large amount of coordinated water. The excellent optical and structural
properties make these NIR-emitting nanoparticles promising in applications
as biological probes. |
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144. Zhenhua Bai, Minoru Fujii, Yuki Mori, Yuji Miwa, Minoru Mizuhata, Hong-Tao
Sun, and Shinji Hayashi,
Efficient Near-infrared Emission from
Neodymium by Broadband Sensitization of Bismuth in Zeolites
Optics Letters, Vol. 36, No. 6,
pp. 1017-1019 (2011) . |
| Nd-Bi codoped zeolites were prepared by an ion-exchange process,
and the optical properties were investigated by photoluminescence (PL)
and PL excitation spectra, and decay time measurements. The results show
that the NIR emission of Nd3+ ions is significantly enhanced by the introduction
of bismuth in codoped samples, and the lifetime reaches 246 μs. It is also
observed that NIR-active Bi acts as a sensitizer of Nd3+ ions. The energy
transfer efficiency is also estimated. The peculiar optical properties
make Nd-Bi codoped zeolites promising for potential application in biological
probes. |
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137. Hong-Tao Sun, Yoshio Sakka, Yuji Miwa, Naoto Shirahata, Minoru Fujii, and Hong Gao
Spectroscopic Characterization of Bismuth Embedded Y Zeolites
Applied Physics Letters, Vol. 97, 131908 pp. 1-3 (2010). |
| Bismuth embedded Y zeolites were studied by using UV-vis- near infrared
(NIR) diffuse reflectance, Raman, and steady-state NIR photoluminescence
spectroscopy. The results suggest that Bi53+ and Bi+ active centers coexist
in the dehydrated and hydrated zeolite framework, both of which contribute
to NIR emission. Furthermore, it was revealed that the high-temperature
annealing leads to the formation of Bi2O3 clusters, which act as blocks
for selectively closing down the “in-out windows” of H2O and O2 molecules
in the zeolites. It is believed that these materials can find a wide array
of applications as active media of broadly tunable micro or nano-optical
sources. |
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131. Zhenhua Bai, Hong-Tao Sun, Takashi Hasegawa, Minoru Fujii, Fumiaki Shimaoka,
Yuji Miwa, Minoru Mizuhata, and Shinji Hayashi,
Efficient near infrared luminescence and energy transfer in erbium/bismuth co-doped zeolites
Optics Letters, Vol. 35, Issue 11, pp. 1926 - 1928 (2010) . |
| We have shown that tunable and highly efficient broadband near-IR (NIR)
luminescence can be realized in erbium/bismuth codoped zeolites. The emission
covers the ranges of 930–1450nm and 1450–1630nm. The intensity ratio of
the two bands can be tuned by adjusting the concentration of erbium and
the excitation wavelength. Steady-state and time-resolved photoluminescence
(PL), and PL excitation measurements indicate that two kinds of emitters
coexist in the pores of zeolites, and that NIR active bismuth simultaneously
acts as a sensitizer of erbium. The present results demonstrate an important
rational strategy for the design of a tunable NIR-emitting zeolite-based
nanosystem. |
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125. Hong-Tao Sun, Akinobu Hosokawa, Yuji Miwa, Fumiaki Shimaoka,Minoru Fujii, Minoru Mizuhata, Shinji Hayashi, and Shigehito Deki
“Strong Ultrabroadband Near-Infrared Photoluminescence from Bismuth Embedded Nanocrystalline Zeolites and Their Derivatives,”
Advanced Materials, Vol. 21, pp. 3694–3698 (2009). |
| Zeolites with embedded bismuth compounds display strong, air-stable, long-lived, ultrabroadband, and tunable near-infrared photoluminescence (see picture). Bismuth ions not only act as luminescence-active centers, but also as blocks for selectively closing the “in–out windows” of water molecules. Bismuth active centers can be sealed in a low-vibrational environment by bismuth agglomerates even when the sample still contains a large amount of water. |
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117. Hong-Tao Sun, Takashi Hasegawa, Minoru Fujii, Fumiaki Shimaoka,
Zhenhua Bai, Minoru Mizuhata, Shinji Hayashi, and Shigehiko Deki,
"Highly-Efficient and Air-stable Near Infrared Emission in Erbium/Bismuth Codoped Zeorites,”
Applied Physics Letters, Vol. 94, 141106, pp. 1-3 (2009). |
| We have shown that highly efficient and air-stable 1531 nm emission can
be realized in erbium/bismuth codoped zeolites. The luminescence lifetime
of Er3+ at 1531 nm can reach up to 4.2 ms. Bismuth compounds formed by
high temperature annealing can act as blockages of selectively closing
down the “in-out windows” of water molecules, i.e., Er3+ ions are sealed
in a low-vibrational environment by bismuth agglomerates even when the
samples contain a large amount of water. This finding may pave the way
for the applications of active ions doped porous materials in infrared
photonics. |
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116. Hong-Tao Sun, Y. Miwa, Fumiaki Shimaoka, Minoru Fujii, A. Hosokawa, Minoru Mizuhata, Shinji Hayashi, and Shigehito Deki,
"Superbroadband Near Infrared Nano Optical Source Based on Bismuth Doped High-silica Nanocrystalline,”
Optics Letters, Vol. 34, Issue 8, pp. 1219-1221 (2009).
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| We have shown that efficient superbroadband near-IR luminescence can be
realized in bismuth-doped high-silica nanocrystalline zeolites. The emission
band covered the range of 930-1620 nm, with a maximum peak at 1146.3 nm,
an FWHM of 152 nm, and a lifetime of over 300 μs under the excitation of
a 488 nm laser line. The observed luminescence was attributed to subvalent
Bi (Bi+) ions formed in the annealed zeolites. These Bi-doped nanozeolites
may find applications as superbroadband near-IR nano-optical sources. |
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115. Hong-Tao Sun, Takashi Hasegawa, Minoru Fujii, Fumiaki Shimaoka, Zhenhua Bai, Minoru Mizuhata, Shinji Hayashi, and Shigehito Deki,
"Significantly Enhanced Superbroadband Near Infrared Emission in Bismuth/Aluminum Doped High-Silica Zeolite Derived Nanoparticles,”
Optics Express, Vol. 17, No. 8, pp. 6239-6244 (2009). |
| Significantly enhanced superbroadband near infrared emission has been realized in bismuth/aluminum doped high-silica zeolite derived nanoparticles. The emission intensity can be easily tailored by the introduction of aluminum. The luminescence lifetime can reach up to 695 μs. The results reveal that the existence of charge imbalance environment caused by [AlOV4/2]- units in host materials is requisite to the formation of infrared-active Bi+. The finding presents a feasible route to design highefficient bismuth activated infrared luminescent nanoparticles. These bismuth doped nanoparticles may find applications as superbroadband near infrared nano optical sources. |
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