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

Abstract

AbstractHexagonal NaYF4: Er3+/Yb3+ (β‐NaYF4) 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‐NaYF4: Er3+/Yb3+ (α‐NaYF4) nanoparticles were transformed into β‐NaYF4 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‐NaYF4 microprisms was further improved via regulating the concentration of chelating agents and pH values in the precursor solution. β‐NaYF4 microprisms displayed red and green color emissions for 980 nm excitation owing to the 4F9/2 and 2H11/2/4S3/2 → 4I15/2 transitions of Er3+ respectively. The ratio (2H11/2/4S3/2 → 4I15/2) between green fluorescence intensities (FIR) of β‐NaYF4 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‐NaYF4 microprisms in measuring the laser‐induced heating effects.