Efficient multi-functional erbium-doped lithium yttrium fluoride phosphor synthesized by novel microwave-assisted combustion technique for diverse applications

Abstract

It is aimed at investigating the structural and optical properties of LiYF₄: Er phosphor material to realize its ability in multi-functional applications. Samples were prepared by the microwave-assisted combustion route that is the most feasible technique to prepare the bulk amount of samples in a short time. The LiYF₄ sample possessed the lower maximum phonon energy of 563 cm⁻¹ that favors luminescence. Based on the upconversion emission under different concentrations, pump powers, and temperatures, it is ensured that the prepared phosphor has multi-functional capability. It can be used to improve the solar cell performance, to detect the invisible IR radiation, and to measure the temperature through optical thermometry where conventional methods cannot be performed. We have developed a device based on resin-coated LiYF₄: Er phosphor film to detect the harmful and invisible near infrared (NIR) radiation. The device has significantly produced visible emission when it is irradiated with NIR laser beam. Three types of modes have been applied in four ways to determine the sensitivity of the phosphor system, i.e., (1) fluorescence intensity (FI), (2) fluorescence intensity ratio (FIR) of (i) thermally coupled (TCL) and (ii) non-thermally coupled energy levels (NTCL), and through (3) CIE chromaticity coordinates. The maximum relative sensitivity (S_r) of 1.47 %K⁻¹ is achieved by FI_{551 nm} mode at 320 K, it has maintained the above 1 %K⁻¹ till 440 K and the least value it has delivered is 0.79 %K⁻¹ at 520 K. The CIE coordinates mode exhibited the appreciable relative sensitivity of 0.21 %K⁻¹ at 540 K in this mode. The most benefit thing in this mode is that the relative sensitivity improves with temperature since it exhibited stable absolute sensitivity of 0.08 × 10⁻² K⁻¹ in the range of 300–540 K.