Near-Infrared-to-Near-Infrared Optical Thermometer BaY2O4: Yb3+/Nd3+ Assembled with Photothermal Conversion Performance

Achieving Near-Infrared Highly Sensitive Temperature Sensing in Lanthanide-Doped Lead-Free Double Perovskite NaLaMgWO6 with Significant Thermal Enhancement

The significant temperature response of lanthanide-doped up-conversion luminescent materials is typically characterized by a severe thermal quenching of the luminescence intensity at elevated ambient temperatures, which severely restricts materials' capability in temperature sensing. Herein, the influence of matrix phonon properties on the remarkable thermal enhancement effect in the thermosensitive material NaLaMgWO6:Yb3+/Nd3+ is reported. It is elucidated that achieving a significant thermal enhancement of Nd3+ with a higher phonon energy oxide matrix is easier than a halide matrix, which has lower phonon energy by comparison with previous findings. Interestingly, the emission of thermally related levels gets enhanced to various extents through phonon-assisted thermal population. In light of this, a three-model thermometer is constructed based on luminescence intensity ratio (LIR) technology. Given that Sr and ΔE possess a positive correlation, it is feasible to acquire greater temperature monitoring sensitivity Sr in Nd3+, which has a larger ΔE. At 313 K, this thermometry model may achieve a maximum sensitivity of 2.84%·K-1. This work not only provides guidance for the selection of efficient near-infrared up-conversion material but also opens up a prospect for the realization of ultrasensitive thermally coupled luminescent thermometers.

Multifunctional Optical Sensing with Lanthanide-Doped Upconverting Nanomaterials: Improving Detection Performance of Temperature and Pressure in the Visible and NIR Ranges

Temperature and pressure are fundamental physical parameters in the field of materials science, making their monitoring of utmost significance for scientists and engineers. Here, the NaSrY(MoO4)3:0.02Er3+/0.01Tm3+/0.15Yb3+ nanophosphor is developed as an optical sensor material. Under 975 nm laser excitation, the upconversion characteristics and optical detection performance of the multifunctional sensing platform of temperature and pressure (vacuum) are investigated. We have successfully developed a novel detection platform that enables optical detection of pressure (vacuum) and temperature. This platform utilizes thermally coupled levels (TCLs) and non-TCLs of Er3+ and Tm3+ to achieve ratiometric detection. The multimodal optical temperature and pressure detection based on TCLs and non-TCLs is successfully realized by using different emission bands of double emission centers, which makes it possible for self-referencing optical temperature and pressure measurement modes. These results indicate that the developed nanophosphor is a promising candidate for optical sensors, and our findings suggest potential strategies for modulating the sensor properties of luminescent materials doped with rare-earth ions.

Insights into NdIII to YbIII Energy Transfer and Its Implications in Luminescence Thermometry

This work challenges the conventional approach of using NdIII 4F3/2 lifetime changes for evaluating the experimental NdIII → YbIII energy transfer rate and efficiency. Using near-infrared (NIR) emitting Nd:Yb mixed-metal coordination polymers (CPs), synthesized via solvent-free thermal grinding, we demonstrate that the NdIII [2H11/2 → 4I15/2] → YbIII [2F7/2 → 2F5/2] pathway, previously overlooked, dominates energy transfer due to superior energy resonance and J-level selection rule compatibility. This finding upends the conventional focus on the NdIII [4F3/2 → 4I11/2] → YbIII [2F7/2 → 2F5/2] transition pathway. We characterized Nd0.890Yb0.110(BTC)(H2O)6 as a promising cryogenic NIR thermometry system and employed our novel energy transfer understanding to perform simulations, yielding theoretical thermometric parameters and sensitivities for diverse Nd:Yb ratios. Strikingly, experimental thermometric data closely matched the theoretical predictions, validating our revised model. This novel perspective on NdIII → YbIII energy transfer holds general applicability for the NdIII/YbIII pair, unveiling an important spectroscopic feature with broad implications for energy transfer-driven materials design.

Manipulating the thermometric behaviors of Er3+/Yb3+/Ho3+-tridoped La2Mo3O12 polychromatic upconverting microparticles via adjusting spatial mode and a sensing strategy

To meet the needs of contactless optical thermometry, Er3+/Yb3+/Ho3+-tridoped La2Mo3O12 (LMO) microparticles were designed and synthesized. Upon exciting with 980 nm light, the synthesized compounds emit glaring upconversion (UC) emissions and their emission colors can be tuned from green to yellow by altering the Ho3+ content. It is found that the optimal doping contents for Yb3+ and Ho3+ in LMO are 9 and 1 mol%, respectively, and the UC emission mechanism involved is a two-photon harvest process. Using the fluorescence intensity ratio (FIR) technique to analyze the temperature responses of the UC emissions arising from thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs), the temperature sensing abilities of the synthesized samples were investigated. When the TCLs of Er3+ (2H11/2, 4S3/2) are used, the synthesized microparticles present the highest absolute and relative sensitivities of 0.0085 and 1.0236% K-1, respectively. Moreover, when the non-TCLs of Er3+ (2H11/2) and Ho3+ (5F5) are used, the maximum absolute and relative sensitivities of the synthesized compounds are 0.0296 and 0.6287% K-1, respectively. Clearly, the thermometric characteristics of the final products can be regulated via using different sensing strategies (i.e., TCLs and non-TCLs) and emission combinations (i.e., spatial mode). However, the change of the Ho3+ content has little impact on the temperature sensing capacity of the synthesized products. These results indicate that Er3+/Yb3+/Ho3+-tridoped LMO microparticles are promising candidates for optical thermometers and our findings also provide possible strategies for regulating the thermometric properties of rare-earth ion doped luminescent materials.

Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF₄:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H₂O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K^-1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.