Synthesis and design of NaYF₄ microprisms via a microwave‐assisted approach for highly sensitive optical thermometry applications

Abstract

Hexagonal NaYF 4 : Er 3+ /Yb 3+ (β-NaYF 4 ) microprisms with uniform particle sizes were synthesized via a microwave-assisted hydrothermal method (MWHM). Nucleation and crystal growth were significantly surpassed owing to the microwave irradiation.Cubic-NaYF 4 : Er 3+ /Yb 3+ (α-NaYF 4 ) nanoparticles were transformed into β-NaYF 4 microprisms with reaction time in between 10 and 120 minutes at 180°C. The shape of the particles was enhanced via controlling the nucleation process with optimized irradiation duration and heating rates. The size distribution of β-NaYF 4 microprisms was further improved via regulating the concentration of chelating agents and pH values in the precursor solution. β-NaYF 4 microprisms displayed red and green color emissions for 980 nm excitation owing to the 4 F 9/2 and 2 H 11/2 / 4 S 3/2 → 4 I 15/2 transitions of Er 3+ respectively. The ratio ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) between green fluorescence intensities (FIR) of β-NaYF 4 microprisms was recorded with the variation in temperature from 303 K to 550 K. The recorded FIR values obeyed Boltzmann distribution and the distribution was used to evaluate the sensitivity. The optimum absolute sensitivity was achieved as 0.0044 K −1 at 490 K with promising resolution, reversibility, and stability. Furthermore, the power-dependent variations in FIR values implied the suitability of β-NaYF 4 microprisms in measuring the laser-induced heating effects.

Advances in Synthesis Strategies for Lanthanide-based NaYF4 Upconversion Nanocrystals and Their Applications in Ratiometric Thermometry

“…Microwave-aided approaches: Som et al [122] used a microwave-enhanced hydrothermal method to synthesize hexagonal-phase NaYF 4 micro prisms with enhanced UC emission peaks. This method reduces the reaction time and offers uniform morphology, but optimizing parameters and achieving precise control over size is not easy.…”

“…Som et al recently synthesized Microparticles of hexagonal NaYF 4 co-doped with Er 3+ and Yb 3+ using a microwave-enhanced hydrothermal method, resulting in uniform morphology and a pure phase within a shorter reaction time, which is shown in Figure 2. The reaction parameters influenced the phase and morphology, with a notable transformation from cubic to hexagonal phase as the reaction duration increased from 10 minutes to 2 hours at 180 • C. Optimized conditions yielded β-NaYF 4 micro prisms with narrow size distributions and enhanced UC emission peaks at 524 nm, 545 nm, and 659 nm upon 980 nm excitation, attributed to Er 3+ ion transitions [122].…”

“…Subsequently, studies like Kramer et al in 2004 [120] refined the synthesis, prioritizing efficiency, stability, and phase optimization, setting a benchmark for subsequent techniques. The quest for microscale par- ticles witnessed innovative approaches by Zheng et al [121] and Som et al [122], leveraging hydrothermal and microwaveenhanced methods, respectively, to achieve controlled morphologies and distinct emission behaviors, unlocking the potential for higher-order UV emissions in Er 3+ -doped microcrystals.…”

Two‐wavelength excitation–driven robust operation of green up‐conversion emission in Er3+‐doped oxyfluoride glass–ceramic

“…Photonic glass ceramics (GCs), especially oxyfluoride GCs, combining the advantages of glass (simple fabrication, low loss, tunable optical properties, and high thermochemical stability) 12 and fluoride crystal (low phonon energy), [13][14][15][16] can significantly improve the optical performance of active ions. It has been demonstrated that the weak interaction between photons will deteriorate the optical modulation performance.…”