Ratiometric Optical Thermometry in Lanthanide-Doped Molybdate Phosphors via Construction of Diverse Charge-Transfer Bands

Abstract

Optical temperature measurement of fluorescence intensity ratio has the advantages of noncontactness and fast response, so it has been widely studied by scholars. It is difficult to obtain high sensitivity in temperature measurement using a traditional thermally coupled energy-level method. Herein, two different charge-transfer bands are constructed to activate phosphors, and two different emission bands in dual-luminescent centers are used to raise the temperature sensitivity. Tb 3+ and Eu 3+ dual-doped molybdate phosphors were successfully synthesized, and the host material was sensitized by the chargetransfer state. The absorption energy of MoO 4 2− was transferred to Tb 3+ and Eu 3+ ions by a resonance interaction, and the spectra of both the ions overlapped greatly, which indicates that there is energy transfer between Tb 3+ and Eu 3+ . Multiphonon de-excitation is the thermal quenching mechanism of lanthanides because Tb 3+ has smaller thermal quenching activation energy and faster quenching speed. The fluorescent powder has good temperature sensitivity in the temperature range of 303−503 K, and the maximum relative sensitivity and absolute sensitivity are 1.1% K −1 (483 K) and 0.017 K −1 (503 K), respectively, which are generally superior to those of the previous optical materials. In addition, with an increase of temperature, the luminescent color of the developed phosphor changes from yellow-green to white. To sum up, the prepared phosphors have excellent potential to be used as temperature sensors as well as temperature indicators.

Local Structure Regulation in Near-Infrared Persistent Phosphor of ZnGa2O4:Cr3+ to Fabricate Natural-Light Rechargeable Optical Thermometer

“…As a matter of fact, the optical materials used for temperature measurement with a real-time response may have high sensitivity and appropriate temperature resolution. In addition, the temperature probe/sensor could be stable to recycle use. − In the past few years, several kinds of luminescent materials have been proposed for temperature probes/sensors. ,, The temperature-dependent spectroscopic results in quantum dots and carbon dots were presented and developed; − metal–organic complexes and frames have also been fully developed for temperature sensors; ,− at the same time, a lot of organic dyes were chosen for the luminescence temperature measurement, including rhodamine B, polymeric nanoparticles, dipropylene glycol tert -butyl ether (DPTB) dissolved in MOE, carbazole-substituted dicyanobenzenes, and anthraquinone-based intramolecular charge-transfer dyes, and so on. ,,, In addition, rare-earth phosphors, including NaYF 4 :Yb 3+ ,Er 3+ , Y 2 O 3 :Eu 3+ ,Nd 3+ , SrAl 2 O 4 :Eu 2+ ,Dy 3+ , and KBaY­(MoO 4 ) 3 :Tb 3+ ,Eu 3+ have been widely used for the temperature measurement ,,, because of their temperature-dependent fluorescence intensity ratio (FIR). Moreover, as the lifetime of the phosphors doped with transition metal ions is sensitive to temperature, these phosphors are the potential thermometry materials. , …”

Realization of an Optical Thermometer via Structural Confinement and Energy Transfer

“…The electrons jump back to the ground state in the absence of radiative transition through emitting phonons. Such a process is defined as multi-phonon de-excitation (MPD), and it is consistent with the energy gap rule. , The distinct thermal quenching performance has been indicated by the activation energy ( E a ) of Bi 3+ ions and Eu 3+ ions. The estimation is expressed by the Arrhenius equation where I 0 and I T are defined as the initial PL intensity and the PL intensity at different temperatures, respectively, A is the constant, and k means the Boltzmann constant (8.62 × 10 –5 eV/K).…”

“…Such a process is defined as multi-phonon deexcitation (MPD), and it is consistent with the energy gap rule. 9,43 The distinct thermal quenching performance has been indicated by the activation energy (E a ) of Bi 3+ ions and Eu 3+ ions. The estimation is expressed by the Arrhenius equation 44 i k j j j j j y…”

“…Temperature has significant influence on daily life, industrial processes, and scientific research. − Therefore, it is compulsory to measure or detect the temperature quickly and accurately. , Recent studies concerning the fluorescence intensity ratio (FIR) technique have provided a new way for thermal sensing due to its fast responsive rate, superior sensitivity, and simple operation. , Especially, in terms of harsh environments or micro- and high-speed moving objects, FIR fluorescent sensors have significant advantages as compared to conventional contact temperature measurement methods such as noninvasiveness and anti-environment interference. , In general, the FIR temperature measurement is realized by monitoring the relative ratio variation of two distinct emission intensities relative to temperature, which will be effective to circumvent the influence of the emission intensity variation induced by other factors . Most of the FIR fluorescent sensors are based on the temperature-induced inverse electron population at thermally coupled levels (TCLs) from traditional lanthanide elements including Gd 3+ , Ho 3+ , Er 3+ , and Tm 3+ ions. − However, such reported optical thermometers generally have very low signal discriminability.…”

“…6,7 Especially, in terms of harsh environments or micro-and highspeed moving objects, FIR fluorescent sensors have significant advantages as compared to conventional contact temperature measurement methods such as noninvasiveness and antienvironment interference. 8,9 In general, the FIR temperature measurement is realized by monitoring the relative ratio variation of two distinct emission intensities relative to temperature, which will be effective to circumvent the influence of the emission intensity variation induced by other factors. 10 Most of the FIR fluorescent sensors are based on the temperature-induced inverse electron population at thermally coupled levels (TCLs) from traditional lanthanide elements including Gd 3+ , Ho 3+ , Er 3+ , and Tm 3+ ions.…”