Temperature-sensing characteristics of NaGd(MoO4)2: Sm3+, Tb3+ phosphors

In this study, Sm³⁺/Tb³⁺-co-doped NaGd(MoO₄)₂ phosphors were prepared via the hydrothermal method, with sodium citrate used as a chelator. X-ray diffraction confirmed the structure of the samples, and the test outcomes showed that the phosphors exhibited a body-centered tetragonal structure. Field-emission scanning electron microscopy results showed that the specimen morphology changed with the change in the Cit^3?/Re³⁺ molar ratio. Moreover, the measured temperature-dependent emission spectra showed that Sm³⁺ and Tb³⁺ had different quenching trends; thus, the fluorescence intensity ratio can be used to represent temperature. In addition, the outcome of this experiment revealed that the temperature-sensing sensitivity of the phosphors gradually increased with the increasing Cit^3?/Re³⁺ ratio, and the highest sensitivity value was 0.346 K^?1 (at 503 K, Cit^3?/Re³⁺ = 2). When the temperature was 298–369 K, the temperature-sensing relative sensitivity increased with increasing Cit^3?/Re³⁺, but in the range 374–503 K, the relative sensitivity decreased with increasing Cit^3?/Re³⁺. The highest relative sensitivity value of the sample was 2.7% K^?1 (404 K, Cit^3?/Re³⁺ = 0). Additionally, the Commission International del’Eclairage chromaticity coordinates displayed that the luminous colors of Sm³⁺/Tb³⁺-co-doped specimens continuously changed from green to red as the temperature changed.     

Yb/Er/Ho-α-SiAlON ceramics for high-temperature optical thermometry

Maximum operating temperature in optical thermometry is limited due to poor thermal stability of the sensing material at high temperatures. Here, Yb, Er and Ho-doped α-SiAlON (Yb/Er/Ho-α-SiAlON) ceramic prepared by hot press method has been studied for optical thermometry via upconversion under 980 nm excitation. The phase of the sintered ceramic has been confirmed by Rietveld refinement of the X-ray diffraction data. The temperature-dependent upconversion was studied in a wide temperature range of 298–1023 K and fluorescence intensity ratio technique was used for temperature sensing behavior. Excellent spectral/thermal stability over the investigated temperature range was observed for the Yb/Er/Ho-α-SiAlON as the sensing material. The maximum values of absolute and relative sensitivity based on the thermally coupled levels of Er³⁺ are 59.2 × 10^?4 K^?1 and 1.10 %.K^?1 at 298 K and that based on non-thermally coupled levels are 108 × 10^?4 K^?1 at 385 K and 0.345 %.K^?1 at 329 K, respectively.     

荧光纤维的特性研究

以湿法成型制得荧光薄膜、熔融纺丝制得荧光纤维为样品,研究了荧光粉含量、凝固浴和拉伸倍数对荧光强度的影响,并对荧光牢度(耐光性)进行了研究,还从耐洗涤、耐高温、耐溶剂、耐酸碱四方面对其性能稳定性进行了研究。     

Ultra-sensitive low-temperature thermometer regulated by the crystal field strength

Developing novel optical thermometry with ultrahigh relative sensitivity and temperature resolution has become a cutting-edge topic. For this purpose, under obeying Boltzmann distribution, a series of Li₂Zn_0.9992-xA_xGe_3-yB_yO₈:0.08% Cr³⁺ (B= Sc³⁺, In³⁺, A = Si⁴⁺) phosphors were studied, which the luminescence intensity ratio between the transition of ⁴T_2g→⁴A_2g emission and the R line based on thermally coupled energy levels constitutes a temperature sensing work with a relative sensitivity of 9.46% K^?1, 9.73% K^?1, and 10.38% K^?1, respectively. It is worth mentioning that the luminescence intensity of the R line (peak 1) increases significantly with the increase of temperature, while the transition of ⁴T_2g→⁴A_2g (peak 2) with high intensity at low temperature gradually quenching, and this opposite trend is an important advantage for the design of excellent thermometers. Compared the best relative sensitivity of Li₂Zn_0.9992-xA_xGe_3-yB_yO₈:0.08%Cr³⁺ (B= Sc³⁺, In³⁺, A = Si⁴⁺) with the crystal field Dq/B, it can be concluded that relative sensitivity increasing gradually with decreasing the intensity of crystal field. Finally, by testing the stability of the sample at 50 K, a thermal resolution of 0.082 K, 0.080 K and 0.077 K was obtained, respectively, which is one of the best thermal resolutions so far, while the repeatability of the sample stability at 50 K and 300 K cycles was higher than 99%. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr³⁺-based luminescence intensity ratio thermometers.     

Improving the NIR light‐harvesting of perovskite solar cell with upconversion fluorotellurite glass

Upconversion glasses are capable of converting the sub‐bandgap NIR light into photons of a particular wavelength which can be efficiently utilized by solar cells. Herein, the Yb³⁺/Er³⁺ co‐doped fluorotellurite upconversion glasses were prepared. The most intense upconversion luminescence (UCL) under 980‐nm LD excitation was obtained in the glass with Yb³⁺‐to‐Er³⁺ molar ratio of 10:1. The dependences of UCL on the pump power and temperature were investigated. The UCL can be mainly attributed to the two‐photon involved energy transfer processes and is very stable to the change in temperature even when heated up to 200°C. The subsequent implementation of the glass as upconverter for a MAPbI_3‐xCl_x‐based perovskite solar cell (PSC) resulted in an open circuit voltage of 0.83 V and a short circuit current density of 0.32 mA/cm². This application of upconversion glass for enhancing the NIR light harvesting offers a promising way to improve the photo‐electric conversion efficiencies of PSCs.     

Multicolor upconversion emission and highly optical temperature sensing based on lanthanide-doped double perovskite Sr2LaNbO6 phosphors

Here we adopt trivalent lanthanide (Ln³⁺ = Er³⁺, Er³⁺/Ho³⁺, and Yb³⁺/Tm³⁺) doped Sr₂LaNbO₆ (SLNO) as novel upconversion luminescence (UCL) materials for achieving UCL and optical temperature sensing under 980 nm excitation. Specifically, Er³⁺ single doped Sr₂LaNbO₆ phosphors present bright high-purity green emission under the 980 nm excitation. While co-doping with the Ho³⁺ ions, the component of red emission from Er³⁺ ions increases significantly and sample show a remarkable enhancement of luminescent intensity relative to SLNO:Er³⁺ sample. The above-mentioned phosphors and Yb³⁺/Tm³⁺ co-doped phosphor (blue emission) successfully achieve high-purity trichromatic UCL and mixed white light output in the same host. Furthermore, the temperature sensing performance of the SLNO:Er³⁺/Ho³⁺ phosphor based on the fluorescence intensity ratio (FIR) is systematically studied for the first time. The temperature sensing based on the non-thermal coupling levels (NTCLs) exhibit higher sensitivity than that based on the thermal coupling levels (TCLs). The maximum absolute and relative sensitivity for ⁴F_9/2/⁴I_9/2 NTCLs reach 0.16803 K^?1 at 427 K and 0.01591 K^?1 at 641 K, respectively. Interestingly, NIR emission of ⁴I_9/2 → ⁴I_15/2 transition presents a thermal enhancement, while visible emissions show thermal quenching. These results indicate that the Ln³⁺ doped Sr₂LaNbO₆ UCL phosphors have potential applications in the fields of non-contact temperature sensors, full-color displays, and anti-counterfeiting.     

Synthesis and optically acid-sensory properties of novel polyoxadiazole derivatives

New organo-soluble and blue-emissive fluorene-based polyoxadiazoles, PFO_x and PFO_xEH, exhibit colorimetric and fluorescent acid-sensory properties to a strong acid due to the weak basicity of imine-type nitrogen atom(s) in an 1,3,4-oxadiazole ring. To further investigate their protonation with an acid, ¹H NMR spectroscopy and AM1 semiempirical quantum-mechanics are utilized as well as UV-visible absorption and fluorescence spectroscopies. These investigations indicate the protonation does not proceed thermodynamically but kinetically at the initial stage of the complex formation of an acid and an oxadiazole ring in the polymer backbone.