Sensors and Actuators A 232 (2015) 8–12
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Sensors and Actuators A: Physical
journal homepage: www.elsevier.com/locate/sna
Use of cross-relaxation for temperature sensing via a fluorescence
intensity ratio
Weiwei Zhang
a,b,∗
, Stephen F. Collins
b
, Greg W. Baxter
b
, Fotios Sidiroglou
b
,
Changkui Duan
c
, Min Yin
c
a
Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China
b
Optical Technology Research Laboratory, Victoria University, P.O. Box 14428, Melbourne, Victoria 8001, Australia
c
Department of Physics, University of Science and Technology of China, Hefei 230026, China
article info
Article history:
Received 24 October 2014
Received in revised form 7 May 2015
Accepted 8 May 2015
Available online 14 May 2015
Keywords:
Temperature
Fluorescence intensity ratio
Energy transfer
abstract
A scheme that provides an alternative mechanism for temperature sensing via a fluorescence intensity
ratio (FIR) is proposed. The rate of energy transfer between rare-earth ions in a crystal or glass host
is temperature dependent, and as such exhibits a changing intensity ratio in the emission spectrum.
Here a phosphor YBO
3
:Eu
3+
was used to illustrate the proposed sensing mechanism. The temperature
dependence of the observed fluorescence is similar to the phenomenon found for the conventional FIR
technique. The potential benefit of the proposed scheme is access to numerous additional varieties of
active materials for FIR temperature sensing.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
The fluorescence intensity ratio (FIR) technique is known as an
absolute temperature sensing method. Various rare-earth ions such
as Eu
3+
,Nd
3+
,Er
3+
and Sm
3+
can be used in the technique [1]. The
ions are generally doped into a glass or crystalline solid to form
the active material. The underlying science has been articulated so
that the performance of the standard FIR technique can be readily
predicted [1,2]. Most recent explorations of the FIR technique focus
on the development of novel materials that display familiar char-
acteristics, whilst reporting slight improvements in temperature
sensitivity.
Various thermal equilibrium systems, inaddition to the FIR tech-
nique, may be utilized for absolute temperature sensing with the
simple requirement that an observable characteristic is tempera-
ture dependent. When considering any thermometer, either optical
or electronic, it is the thermal equilibrium distribution at the atomic
or electron level that dominates temperature dependent changes.
Considering the basic physics principles of such distributions, abso-
lute temperature, T, always appears with the Boltzmann’s constant,
k
B
, to produce energy, k
B
T. A well-known example comes from
∗
Corresponding author at: Jiangxi Engineering Laboratory for Optoelectron-
ics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China.
Tel.: +86 15170463677; fax: +86 791 83953461.
E-mail address: zdw@ustc.edu (W. Zhang).
a semiconductor thermometer whose current-voltage relation
(namely the Shockley equation) includes Boltzmann’s distribution
of carriers. Alternatively, new techniques of temperature sensing
may be developed after investigating the broad array of thermal
distributions of atoms or electrons.
In this article, it is shown that a phosphor with emission lines
from two interactive ions can be exploited successfully as a FIR
material, through efficient cross relaxation between the doped
rare-earth ions. The phosphor YBO
3
:Eu
3+
is used to illustrate the
sensing mechanism.
2. Experimental
The phosphor YBO
3
:Eu
3+
was prepared through a sol–gel pro-
cess. An aqueous solution of rare-earth nitrates was mixed with
tributyl borate, then stirred after adding ethanol until a clear sol was
achieved. The gel formed overnight in a water bath held at 85
◦
C,
and was then baked to form a bulk solid. This was then ground;
the final product was sintered at 900
◦
C for two hours to insure
crystallization.
The phosphor’s luminescence was analyzed with a SPEX-1403
spectrometer under the excitation of a high pressure Hg lamp (out-
put wavelength of 365 nm). In order to investigate the effect of
temperature change on the fluorescence, the phosphor was com-
pressed into a pellet and then glued on a brass heat sink in a
http://dx.doi.org/10.1016/j.sna.2015.05.005
0924-4247/© 2015 Elsevier B.V. All rights reserved.