In an article recently published in the journal Nanomaterials, researchers fabricated glass ceramics containing lead sulfide (PbS) quantum dots (QDs) and evaluated their feasibility for temperature sensing by investigating the PbS glass ceramics’ temperature-dependent luminescence properties at high temperatures.
(a) XRD patterns of precursor glass, GCs and JCPDS Cards No: 02-0669 (PbS); (b) transmission spectra of glass and GCs; (c) TEM and (d) HR-TEM images of GC heat-treated at 500 °C for 10 h; the inset is an enlarged image of (d) containing only one crystal particle. Image Credit: https://www.mdpi.com/2079-4991/14/10/882
Fluorescent Temperature Sensor Advantages
The response rates of commonly used commercial temperature sensors, such as liquid-filled thermometers and thermistors, are relatively slow because they require heat transfer to reach equilibrium. This delay impedes their effectiveness for real-time temperature detection.
In contrast, fluorescent temperature sensors offer a promising alternative. They are easy to fabricate, suitable for real-time temperature sensing, and capable of providing continuous and precise measurements through the monitoring of temperature-dependent fluorescence spectra. The performance of these sensors largely depends on the luminescent centers and the materials that host them.
Glass-ceramic, a composite material that incorporates specific nanocrystals and various glass phases, is an excellent candidate for luminescent material due to the high optical transmittance of glass and the efficient luminescence of the crystals.
However, while various rare-earth-ion-doped glass ceramics have been explored for their luminescent properties in temperature detection, inaccuracies in the luminescence spectrum intensity often arise due to disparities in the photoelectric detector's response. This issue underscores the need for ongoing research into new glass ceramic materials to enhance the capabilities of fluorescent sensors.
Importance of PbS QDs
Semiconductor QDs are well-suited for temperature detection due to observed shifts in their emission spectra—specifically blue shifts and red shifts—with changes in test temperature. PbS QDs, in particular, exhibit tunable emissions in the near- to middle-infrared regions, facilitated by a robust quantum confinement effect and a narrow bandgap. Furthermore, PbS QDs can be precisely precipitated within glass to create glass ceramics, enhancing their utility in temperature sensing. This capability arises from the modulation of the QDs' bandgaps through temperature adjustments, demonstrating their feasibility for such applications.
Additionally, PbS QD glass ceramics are integral in the production of optical fibers, opening significant avenues for the development of innovative fluorescent fiber temperature sensors. Research has primarily focused on the PbS QDs' photothermal properties at low temperatures, ranging from 0 K to room temperature, underlining their potential in diverse sensing environments.
The Study
In this study, researchers prepared glass ceramics embedded with PbS QDs to explore their utility in temperature sensing, particularly examining how their luminescence properties varied with temperatures ranging from room temperature to 210°C. The PbS glass ceramic samples were synthesized using a melt-quenching method followed by heat-treatment processes. The precursor glass molar composition was 31SiO2-29B2O3-10ZnO-25Na2O-3BaO-1.0PbO-1.0ZnS.
The process began by mixing 30 grams of raw materials in the specified ratio in an agate mortar, blending thoroughly for 10 minutes. The mixed powder was then placed in a crucible and heated to 1100 °C for 30 minutes in an electric furnace. After melting, the glass was rapidly poured onto an iron plate and cast into a slab to form the precursor glass samples. These were subsequently heat-treated at temperatures ranging from 480°C to 500°C, producing samples designated as GC-500, GC-495, GC-490, GC-485, and GC-480, based on the specific heat treatment temperatures.
The glass ceramic fibers were fabricated using these PbS glass ceramics as fiber cores through the melt-in-tube technique. The samples were then cut and polished into 2 mm thick slabs.
For analysis, X-Ray diffraction (XRD) assessed the crystalline and amorphous states of the glass ceramics, while high-resolution transmission electron microscopy (HR-TEM) and TEM were employed to evaluate the size distribution and morphology of the nanocrystals within the glass ceramics.
To further explore their properties, the samples' transmission and emission spectra were measured using a UV/VIS/NIR spectrophotometer and a spectrometer, respectively. Researchers also investigated the photothermal properties of these glass-ceramics by placing the samples in a temperature control box and recording the changes in their emission spectra, demonstrating the potential applications of PbS glass ceramics in temperature-sensitive environments.
Significance of the Study
This study revealed that when PbS QDs were precipitated from the glasses, the resulting glass ceramics exhibited broadband emissions, with emission centers tunable from 1250 nm to 1960 nm by varying heat treatment temperatures. Notably, the emission centers of the glass ceramics displayed blue shifts, moving to shorter wavelengths as environmental temperatures rose from room temperature to 210 °C.
Crucially, the values of these emission shifts increased linearly with the test temperature, proving advantageous for temperature-sensing applications. A standout finding was that a PbS QD glass ceramic-based temperature sensor, specifically the sample heat-treated for 10 hours at 500 °C (GC-500), demonstrated the highest sensitivity at 0.378 nm/°C, coupled with excellent repeatability and stability at high temperatures up to 210 °C. Additionally, the highest sensitivity recorded by a glass ceramic fiber-based sensor reached 0.558 nm/°C.
Overall, this study underscores that PbS QD glass ceramics are highly effective materials for developing fluorescent temperature sensors. Moreover, the glass ceramic fibers present significant potential for the development of fiber temperature sensors, promising robust real-time temperature sensing capabilities in complex, integrated, and compact devices.
Journal Reference
Zha, T., Zhang, P., Jin, X., Long, Y., Huang, T., Jia, H., Fang, Z., & Guan, B. (2023). Glass Ceramic Fibers Containing PbS Quantum Dots for Fluorescent Temperature Sensing. Nanomaterials, 14(10), 882. https://doi.org/10.3390/nano14100882, https://www.mdpi.com/2079-4991/14/10/882
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