JAIST Repository
https://dspace.jaist.ac.jp/

Title

Neodymium(III)-doped Y_3Al_2Ga_3O_12 garnet
for multipurpose ratiometric thermometry: Fromcryogenic to high temperature sensing

Author(s)Back, Michele; Xu, Jian; Ueda, Jumpei; Tanabe,
Setsuhisa

Citation

Journal of the Ceramic Society of Japan, 131(4): 5761

Issue Date

2023-04-01

Type

Journal Article

Text version

publisher

URL

http://hdl.handle.net/10119/18764

RightsCopyright (C) 2023, The Ceramic Society of Japan.
Licensed under the Creative Commons Attribution
4.0 International license (CC BY 4.0).
[https://creativecommons.org/licenses/by/4.0/]

Description

Japan Advanced Institute of Science and Technology

JCS
第131巻

第4号

2023年 4 月 1 日発行（毎月1回1日発行）

ISSN 1348-6535 CODEN: JCSJEW

Japan

-

April

vol.131

Journal of the Ceramic Society of Japan

2023

JCS

Journal of the Ceramic Society of Japan 131 [4] 57-61 2023
DOI-

https://doi.org/10.2109/jcersj2.22167

Japan

FULL PAPER

Neodymium(III)-doped Y3Al2Ga3O12 garnet for multipurpose
ratiometric thermometry: From cryogenic to high temperature sensing
Michele Back1,2,³, Jian Xu2,3, Jumpei Ueda2,4 and Setsuhisa Tanabe2
1

Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, 30170, Mestre, Italy
Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606–8501, Japan
3
International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS),
Tsukuba, Ibaraki 305–0044, Japan
4
Materials Chemistry Frontiers, Japan Advanced Institute of Science and Technology (JAIST),
1–1 Asahidai, Nomi, Ishikawa 923–1292, Japan2

Nd3+-doped Y3Al2Ga3O12 garnet ceramic pellet was prepared by solid state reaction and used as prototype toinvestigate the potential of Nd3+-activated garnet phosphors as Boltzmann thermometers for cryogenic and hightemperature ranges. Despite the conventional use of the near-infrared emitting Nd3+-activated phosphors forbiological applications, their real use is hindered by a low sensitivity in the physiological temperature range.
Instead, the photoluminescence analysis in the 100­800 K range demonstrated interesting performances in boththe cryogenic and high temperature ranges. Indeed, by taking advantage of the Stark levels of 4F3/2 (Z-levels)and the ratio between the emission from the 4F5/2 and the 4F3/2 excited states is possible to build two reliable
Boltzmann thermometers in the same material working in the cryogenic temperature range (100­220 K) and athigh temperatures (300­800 K), respectively.
©2023 The Ceramic Society of Japan. All rights reserved.

Key-words : YAGG, Ratiometric thermometry, Luminescence, Garnet, Boltzmann distribution, Neodymium[Received December 29, 2022; Accepted January 15, 2023]

1. Introduction
In the last decade, the use of luminescent materials as
ratiometric thermometers based on the ratio between theemissions from two excited states has been extensively
investigated.1)­4) Despite the wide variety of thermometersproposed, the use of the luminescent signals originatedfrom two thermally coupled excited states of the same
luminescent center, the so-called Boltzmann thermometers, is still recognized among the most reliable systems.
In this view, the most popular thermometers are based on
Er 3+,5) Nd3+,6)­10) Tm3+ 11),12) but also Cr 3+ 13)­15) ions.
Since the electronic structure of Nd3+ allows to work inthe biological windows by both the excitation and emission, Nd3+-activated phosphors are commonly investigatedas optical thermometers for biological applications.16)­19)
Even though the energy gap of about 900­1000 cm¹1
between the 4F3/2 and 4F5/2 energy levels seems to be quite
promising, the large diﬀerence in the intensity between thetransitions starting from these two excited states results ina large uncertainty at room temperature. On the other hand,when the two Stark levels of the 4F3/2 state (Z1 and Z2) are
employed to build a thermometric parameter, the energy³

Corresponding author: M. Back; E-mail: michele.back@unive.it©2023 The Ceramic Society of Japan

gaps between the excited states are typically of few tens toabout a hundred cm¹1, leading, in the physiological temperature range, to small values of sensitivity.
Luminescent thermometers ﬁnd interesting applications
in many other technological ﬁelds such as catalysis,13),20),21)
microﬂuidic22) and microelectronics,23) to name a few,
making the development of reliable optical thermometerscharacterized by high sensitivities at both cryogenic andhigh temperatures still a challenge.
By using Nd3+-doped Y3Al2Ga3O12 garnet as prototype,
we investigate the potential of this family of materials as
Boltzmann thermometers. Even though the materials are
typically proposed for biological applications, herein we
demonstrate interesting performances in the cryogenic andhigh temperature ranges.

2. Experimental procedure
YAGG:Nd3+ ceramic phosphor with the compositionsof Y2.94Nd0.06Al2Ga3O12 was fabricated by a conventional solid-state reaction method. Y2O3 (99.99 %), Al2O3(99.99 %), Ga2O3 (99.99 %) and Nd2O3 (99.99 %) wereused as raw materials. The starting powder was mixed by aball milling method (Premium Line P-7, Fritsch Co. Ltd.)
with anhydrous alcohol for several hours. The mixed
powder was dried at 80 °C for 36 h, compacted to form aceramic green body (º20 mm, 2 mm thickness) under uni57

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

JCS-Japan

Back et al.: Neodymium(III)-doped Y3Al2Ga3O12 garnet for multipurpose ratiometric thermometry: From cryogenic to high temperaturesensing

axial pressing of 50 MPa, and ﬁnally sintered at 1600 °C
for 10 h in air.
X-ray powder diﬀraction (XRPD) measurements were
performed using a diﬀractometer (XRD6000, Shimadzu)
with Cu K¡ radiation (­ = 1.54056 ¡). The diﬀuse reﬂectance spectra were measured by a spectrophotometer(UV3600, Shimadzu) equipped with an integrating sphere.
Barium sulfate is used as a standard for calibration. Photoluminescence excitation (PLE) spectra were measured by
an InGaAs photodiode (IGA-030-H, Electro-Optical System Inc.) coupled with a short-cut (990 nm) and a long-cut(1300 nm) ﬁlter, a monochromator (SpectraPro-300i, Acton
Research Corporation) and a 100 W halogen lamp (MHAA100W, Moritex Corporation) as excitation source. Photoluminescence (PL) measurements were performed with theuse of a USB-powered LED mount (LEDMT1F, Thorlabs)
with a 590 nm LED (full width half maximum = 16 nm),equipped with a collimator, and collecting with a Si CCD
spectrometer (QE-65Pro, Ocean Optics) coupled with aﬁber. The temperature dependent PL spectra were collectedwith a temperature-controlled stage (10 035 L, Linkam).
All of the spectra were calibrated by means of a standard
halogen lamp (DH-2000CAL, Ocean Optics) to obtain
spectra in the photon ﬂux scale.

3. Results and discussion
Aluminium and gallium-based A3(Al,Ga)5O12 garnets
are among the most interesting families of host compounds
in the optical ﬁeld,24) ﬁnding applications as phosphors (themost famous YAG:Ce3+), persistent luminescent materials25) and lasers (YAG:Nd3+ 26)) characterized by highquantum yields. Indeed, the structure allows to accommodate a wide variety of luminescent ions such as lanthanide
ions in the dodecahedral sites and transition metal ions inboth octahedral and tetrahedral sites [Fig. 1(a)].
As prototype to investigate the potential of Nd3+-doped
garnets as optical thermometers for diﬀerent temperature
regimes, the garnet compound Y3Al2Ga3O12 (YAGG) was
selected. The XRPD pattern conﬁrmed the stabilization of single phase [Fig. 1(b)] in which Nd3+ subthe cubic Ia3d
3+stitutes Y in the dodecahedral site.

Figure 1(c) shows the Kubelka­Munk function calculated by the reﬂectance spectrum and the PL emission andexcitation spectra of YAGG:Nd3+ in the range matchingwith the highly eﬃcient commercial Si-detectors. In thisspectral range, the emission is mainly characterized by the4
F3/2 ¼ 4I9/2 transition falling into the ﬁrst biological window. In addition, the PLE spectrum is composed by aseries of absorption lines due to the f-f transitions of Nd3+
ion allowing the excitation in the whole visible range, anappealing feature from the application point of view.
To access the potential of the system as luminescentthermometer, the temperature dependence of the PL spectra was investigated in the 100­800 K range [Fig. 2(a)].
By increasing the temperature, the emission at about 810
nm due to the 4F5/2 ¼ 4I9/2 transition (I5) clearly increases
with respect to the emission at about 880 nm due to the4
F3/2 ¼ 4I9/2 transition (I3) because of the relative population of the higher lying 4F5/2 excited states with respect
to 4F3/2 [scheme in Fig. 2(b)]. Indeed, the luminescenceintensity ratio of the two transitions used as thermometricparameter should follows a Boltzmann law:
E53
LIR53 ¼ I5 =I3 ¼ B53 exp kB T
where ¦E53 is the energy gap between the 4F5/2 and 4F3/2
excited states, kB is the Boltzmann constant and B53 =g5A5N5/g3A3N3 with gi, Ai and Ni the degeneracy of theemitting level i, the spontaneous emitting rate and the
population of the excited state, respectively.
By plotting the logarithm of the intensity ratio between
the two excited states as a function of the inverse of thetemperature, ln(I5/I3) versus T ¹1, it is possible to determine(i) the energy gap ¦E53 between the excited states and(ii) the temperature range in which the Boltzmann law is
working. The ¦E53 of 879 cm¹1 estimated is in agreementwith the energy gap estimated from the baricenters of
the spectral bands (about 1000 cm¹1). In addition, theBoltzmann plot shows a good linearity starting from about
300 K with a clear deviation for lower temperatures.
Even though the energy diﬀerence between the 4F5/2
and 4F3/2 excited states looks particularly suitable for the

Fig. 1. (a) Schematic structure of the garnet structure, (b) XRPD pattern and (c) Kubelka­Munk function, PL
and PLE spectra of YAGG:Nd3+ exciting at 590 nm and collecting at 1060 nm, respectively.

58

JCS-Japan

Journal of the Ceramic Society of Japan 131 [4] 57-61 2023

(a) Temperature dependence of the PL spectra of YAGG:Nd3+ in the 80­800 K temperature range under
excitation at 590 nm. The spectra are normalized to the 4F3/2 ¼ 4I9/2 emission. (b) Energy level diagram of the
Nd3+ ion in YAGG. Arrows highlight the transitions considered in this work (4F3/2 ¼ 4I9/2, 4F5/2 ¼ 4I9/2, andZ1,2 ¼ R5). (c) Plots of ln(I5/I3) versus T ¹1 to calibrate the thermometer using the 4F5/2-4F3/2 couple. The red line
represents the linear ﬁt of the Boltzmann plot.
Fig. 2.

design of an optical thermometers with high performances
for biological applications, the emission from the higher
lying 4F5/2 state is usually quite weak in the physiologicaltemperature range resulting in unsuitable thermal resolutions. However, the thermal stability of the emission athigh temperatures makes the system particularly interesting for high temperature sensing where the emissions fromthe higher lying 4F5/2 state are relevant.
On the other hand, with the aim of developing thermometers for biological applications, a lot of interest wasdevoted to the use of the two Stark levels (Z1 and Z2) of
the 4F3/2 state. However, the narrow energy gap between
these two levels can be exploited not only in the physiological temperature range but also at low temperature
for cryothermometry. Indeed, the small energy gap value
between the two states is particularly suitable to allow
thermal populations also at low temperatures. The temperature dependent PL emission spectra collected in the 100­
400 K range [Fig. 3(a)] show the relative increase of theemission from the higher lying Z2 state with respect to Z1
by increasing the temperature. In addition, the deconvolution of the spectrum [Fig. 3(b)] allows to estimate anenergy gap between the excited states ¦E12 of 50 cm¹1.
By considering the ratio between the two transitions
from Z1 (I1) and Z2 (I2) as a thermometric parameter:
E12
LIR12 ¼ I2 =I1 ¼ B21 exp kB T
the Boltzmann plot in Fig. 3(c) evidences a clear deviationfrom the expected linearity.
The plot can be divided into two diﬀerent regions and ﬁt
by two diﬀerent linear curves in the temperature ranges of100­220 and 220­400 K. The ﬁt of the low temperature
range allows to estimate an energy gap of 45 cm¹1, in very
good agreement with the spectral estimation in Fig. 3(b),resulting particularly reliable as Boltzmann thermometer.
Instead, the deviation from the linear trend characterized
by the expected ¦E12 at temperatures higher than 220 K(characterized by an energy gap of 105 cm¹1) is not completely understood at the present and could be related tothe involvement of phonons.
To discuss the thermometric performances of the thermometers, we considered the ﬁgure of merit described by
the relative sensitivity Sr and the thermal resolution ¤T,deﬁned as:
1 @LIR
LIR @T
1 ¤LIR¤T ¼
Sr LIR

Sr ¼

where ¤LIR is the uncertainty in the determination of
LIR.
The plot of the Sr values of the two thermometric parameters calculated in the diﬀerent ranges of linearity of the
Boltzmann low [Fig. 4(a)] shows interesting values inboth the cryogenic and high temperature ranges. On theother hand, the thermal resolution values in the cryogenic
range by considering the Z1-Z2 couple are smaller than
1 K in the whole temperature range of linearity of the
Boltzmann plot and the values of the thermometer basedon the 4F5/2-4F3/2 couple evidence an interesting situationin which values around 2 K can be achieved at high temperatures up to 800 K [Fig. 4(b)]. Such appealing values
are due to the strong intensity of Nd3+ in the garnet structure giving high signal-to-noise values.
By considering the high reliability of the Boltzmann
thermometers, the relative sensitivity of 0.45 % K¹1 obtained at 100 K is quite promising, being comparable withthe value reported for state-of-the-art cryogenic Boltzmann
thermometers such as in the case of CaHfO3:Cr 3+ (0.3
% K¹1 at 100 K15)).
In addition, it is worth noting that from the application
point of view, YAGG:Nd3+ is also characterized by an
intrinsic high quantum yield and thermal stability already
exploited for lasing applications, making the system particularly promising.
59

JCS-Japan

Back et al.: Neodymium(III)-doped Y3Al2Ga3O12 garnet for multipurpose ratiometric thermometry: From cryogenic to high temperaturesensing

Fig. 4. Temperature dependence of the relative sensitivity (a)and thermal resolution (b) for the thermometers build by considering the ratio between the emissions of the 4F5/2-4F3/2 couple
and the Z2-Z1 couples.

800 K temperature range. The possibility to design two
reliable thermometric parameters based on the Boltzmann
law in the same material is demonstrated. Furthermore, (i)the high temperature stability makes this system suitablefor high temperature sensing by considering the thermal
equilibrium between 4F3/2 and 4F5/2 excited states up to800 K while (ii) for low temperatures from 100 to 220 K,
the thermometer based on the Z1-Z2 couple is demonstrated to be a suitable and reliable cryogenic thermometer withthermal resolution lower than 1 K in the whole temperature
range.
Acknowledgments Work by M.B. was ﬁnancially supported by the Grant-In-Aid for JSPS Fellows (17F17761).

References(a) Temperature dependence of the PL spectra of
YAGG:Nd3+ in the 100­400 K temperature range under excitation at 590 nm. The spectra are normalized to the Z1 emission.
(b) PL integrated area of the emission bands of Z1,2 ¼ R5 transitions as a function of temperature. (c) Spectral deconvolution of
the PL spectrum. (d) Plots of ln(I2/I1) versus T ¹1 to calibrate thethermometer using the Z2-Z1 couple. The blue line and red line
represent the linear ﬁts.
Fig. 3.

4. Conclusions
In summary, the potential of YAGG:Nd3+ system asluminescent thermal sensor is investigated in the 100­601) C. D. Brites, S. Balabhadra and L. D. Carlos, Adv. Opt.
Mater., 7, 1801239 (2018).
2) M. D. Dramićanin, J. Appl. Phys., 128, 040902 (2020).
3) E. J. McLaurin, L. R. Bradshaw and D. R. Gamelin,
Chem. Mater., 25, 1283­1292 (2013).
4) D. Jaque and F. Vetrone, Nanoscale, 4, 4301­4326(2012).
5) F. Vetrone, R. Naccache, A. Zamarron, A. J.
de la Fuente, F. Sanz-Rodriguez, L. Martinez Maestro,
E. M. Rodriguez, D. Jaque, J. Garcia Sole and J. A.
Capobianco, ACS Nano, 4, 3254­3258 (2010).
6) D. Wawrzynczyk, A. Bednarkiewicz, M. Nyk, W. Strek
and M. Samoc, Nanoscale, 4, 6959­6961 (2012).
7) M. Back, J. Ueda, J. Xu, D. Murata, M. G. Brik and
S. Tanabe, ACS Appl. Mater. Inter., 11, 38937­38945(2019).
8) M. Back, E. Casagrande, E. Trave, D. Cristofori, E.
Ambrosi, F. Dallo, M. Roman, J. Ueda, J. Xu, S.
Tanabe, A. Benedetti and P. Riello, ACS Appl. Mater.
Inter., 12, 55195­55204 (2020).
9) M. Suta, Z. Anric, V. Dordevic, S. Kuzman, M. D.
Dramicanin and A. Meijerink, Nanomaterials-Basel, 10,

Journal of the Ceramic Society of Japan 131 [4] 57-61 2023

543 (2020).
10) M. Back, J. Xu, J. Ueda, A. Benedetti and S. Tanabe,
Chem. Mater., 34, 8198­8206 (2022).
11) W. Xu, X. Gao, L. Zheng, Z. Zhang and W. Cao, Sensor.
Actuat. B-Chem., 173, 250­253 (2012).
12) E. Casagrande, M. Back, D. Cristofori, J. Ueda, S.
Tanabe, S. Palazzolo, F. Rizzolio, V. Canzonieri, E.
Trave and P. Riello, J. Mater. Chem. C, 8, 7828­7836(2020).
13) M. Back, J. Ueda, H. Nabu, M. Fujita, A. Yamamoto, H.
Yoshida, H. Tanaka, M. G. Brik and S. Tanabe, Adv.
Opt. Mater., 9, 2100033 (2021).
14) M. Back, E. Trave, J. Ueda and S. Tanabe, Chem.
Mater., 28, 8347­8356 (2016).
15) M. Back, J. Ueda, M. Brik and S. Tanabe, ACS Appl.
Mater. Inter., 12, 38325­38332 (2020).
16) A. Benayas, B. del Rosal, A. Perez-Delgado, K.
Santacruz-Gomez, D. Jaque, G. A. Hirata and F.
Vetrone, Adv. Opt. Mater., 3, 687­694 (2015).
17) A. Skripka, A. Morinvil, M. Matulionyte, T. Cheng and
F. Vetrone, Nanoscale, 11, 11322­11330 (2019).
18) S. Balabhadra, M. L. Debasu, C. D. S. Brites, L. A. O.
Nunes, O. L. Malta, J. Rocha, M. Bettinelli and L. D.

JCS-Japan

Carlos, Nanoscale, 7, 17261­17267 (2015).
19) P. M. Gschwend, F. H. L. Starsich, R. C. Keitel and
S. E. Pratsinis, Chem. Commun., 55, 7147­7150 (2019).
20) R. G. Geitenbeek, A.-E. Nieuwelink, T. S. Jacobs,
B. B. V. Salzmann, J. Goetze, A. Meijerink and B. M.
Weckhuysen, ACS Catal., 8, 2397­2401 (2018).
21) T. Hartman, R. G. Geitenbeek, G. T. Whiting and B. M.
Weckhuysen, Nat. Catal., 2, 986­996 (2019).
22) R. G. Geitenbeek, J. C. Vollenbroek, H. M. H.
Weijgertze, C. B. M. Tregouet, A.-E. Nieuwelink,
C. L. Kennedy, B. M. Weckhuysen, D. Lohse, A.
van Blaaderen, A. van der Berg, M. Odijk and A.
Meijerink, Lab Chip, 19, 1236­1246 (2019).
23) T. P. van Swieten, T. van Omme, D. J. van den Heuvel,
S. J. W. Vonk, R. G. Spruit, F. Meirer, H. H. Perez Garz,
B. M. Weckhuysen, A. Meijerink, F. T. Rabouw and
R. G. Geitenbeek, ACS Appl. Nano Mater., 4, 4208­
4215 (2021).
24) J. Ueda and S. Tanabe, Opt. Mater. X, 1, 100018 (2019).
25) J. Xu and S. Tanabe, J. Lumin., 205, 581­620 (2019).
26) J. E. Geusic, H. M. Marcos and L. G. Van Uitert, Appl.
Phys. Lett., 4, 182 (1964).

61