ABSTRACT
The preparation of perovskite quantum dots (PQDs) using an in situ inkjet printing method is beneficial for improving the problems of aggregation and photoluminescence (PL) quenching during long-term storage. However, the stability of PQDs prepared using this method is still not ideal, and the morphology of in situ-printed patterns needs to be optimized. To address these problems, this study introduced polymethyl methacrylate (PMMA) into the process of in situ inkjet printing of PQDs and explored the effect of PMMA on the in situ patterning effect of PQDs. The results showed that using a mixed precursor solution containing a small amount of PMMA as the printing ink can slow down the shrinkage process of ink droplets and improve the uniformity of film formation. As the printing substrate, PMMA provided a suitable high-viscosity environment for the in situ growth of PQDs. This could effectively suppress the coffee ring effect. In addition, the interaction between the C=O=C group in PMMA and metal ion Pb2+ in the CsPbBr3 precursor molecules was favourable to enhancing the density of PQDs. The prepared PMMA-coated CsPbBr3 quantum dots (QDs) pattern had high stability and could maintain at 90.08% PL intensity after 1 week of exposure to air.
Subject(s)
Oxides , Quantum Dots , Titanium , Polymethyl Methacrylate , Calcium Compounds , InkABSTRACT
In this work, Yb3+/RE3+ (RE = Er/Ho) co-doped Zn3Mo2O9 phosphors were synthesized by high-temperature solid-state reactions. Under 980 nm excitation, the upconversion (UC) luminescence thermal enhancement was obtained for Zn3Mo2O9:Yb3+/RE3+ phosphors. The green emission intensity of the Zn3Mo2O9:Yb3+/Er3+ sample was increased 5 times from 373 to 573 K. The red emission intensity of the Zn3Mo2O9:Yb3+/Ho3+ sample was enhanced 7.92 times. The anomalous thermal enhancement of UC emission was induced by the negative thermal expansion (NTE) of the Zn3Mo2O9 host. The energy transfer rate from the sensitizer (Yb3+) to the activator (RE3+) was enhanced because of the lattice contraction and distortion for NTE materials. Compared with the UC emission of Er3+single doped Zn3Mo2O9 sample, the luminescence thermal enhancement was absent, which contributed to proving the physical mechanism. The temperature sensing properties of the Zn3Mo2O9:Yb3+/Er3+ and Zn3Mo2O9:Yb3+/Ho3+ samples were also investigated based on the fluorescence intensity ratio (FIR) technology. The absolute sensitivity (SA) and relative sensitivity (SR) of Zn3Mo2O9:Yb3+/Er3+ phosphor reached 0.0060 K-1 and 0.72% K-1, which is based on the thermal coupling levels (2H11/2, 4S3/2) FIR of Er3+ ions. In addition, the SA and SR of Zn3Mo2O9:Yb3+/Ho3+ phosphor reached 0.0119 K-1 and 0.86% K-1, that is based on the non-thermal coupling levels (5S2/5F4, 5F5) FIR of Ho3+ ions. The research results indicate that the Zn3Mo2O9 host shows NET. The Yb3+/RE3+ co-doped Zn3Mo2O9 phosphors are good materials for highly sensitive optical temperature measurement, which can be used to develop thermally enhanced ratiometric optical thermometers.
ABSTRACT
Phosphors with rare earth (RE) ions are widely applied to optical temperature measurements. Moreover, the near-infrared (NIR) emission of phosphors has potential applications in the biological field. Herein, Gd2O3:x%Nd3+/Yb3+(0.2 ≤ x ≤ 0.8) samples are successfully synthesized by the sol-gel method, and their phase and morphology are characterized. The XRD data are refined by Rietveld. Under 980 nm continuous wave (CW) laser excitation, the upconversion (UC) and downshift (DS) emissions are studied. The temperature sensing performances of thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs) of Gd2O3: Nd3+/Yb3+ phosphors are investigated through the fluorescence intensity ratio (FIR) technology. In the temperature range of 303-523 K, the maximum relative sensitivity of I761 nm/I550 nm reaches 6.54% K-1, which is based on non-TCLs. At the same time, the maximum relative sensitivity of I761 nm/I1000 nm-1500 nm reaches 3.13%. In addition, the influence of the laser induced heating (LIH) effect is studied. Compared with square wave (SW) pumping, the relative sensitivity would decrease at CW excitation. Finally, the durability and temperature uncertainty are also discussed. The results prove that the Gd2O3:Nd3+/Yb3+ samples present higher relative sensitivity and durability and lower temperature uncertainty in the biological window. Therefore, the phosphors can be used as optical thermometers in the biological field.
