Síntese de nanossensores raciométricos luminescentes de temperatura à base de ZnSMn e carbon dots

Abstract

The continuous search for new technologies capable of meeting the growing demands of the global temperature sensor market drives research and scientific advances, particularly in the field of luminescent nanomaterials with ratiometric emission. In this context, this study developed and evaluated, for the first time, the structural and optical properties of nanocomposites based on manganese-doped zinc sulfide (ZnS) and carbon dots (CD) derived from lemon peels (CD-L), aiming at the creation of ratiometric luminescent nanothermometers. The nanocomposites were synthesized via coprecipitation at room temperature, presenting a spherical morphology and an average size of less than 10 nm. X-ray diffraction (XRD) analyses confirmed the cubic crystalline structure of ZnS, which maintained its crystallographic profile without significant changes after the incorporation of CD-L. The optical properties were investigated by diffuse reflectance spectroscopy (DRS) and ultraviolet-visible (UV-Vis) spectroscopy, revealing absorption bands at 270 nm for ZnS and between 200 – 400 nm, associated with the π-π* and n-π* transitions of CD-L. Additionally, the nanocomposites demonstrated dual emission, with maximum fluorescence centered at 594 nm, characteristic of the 4T1 → 6A1 transition of the Mn²⁺ ion in the ZnS matrix, and at 440 nm, corresponding to the CD-L emission. In thermometric studies, the ZnS (1.0)/CD2 and ZnS (1.0)/CD4 nanosystems exhibited ratiometric responses in the range of 30 to 55°C, with relative thermal sensitivities of 1.04 and 1.11%°C⁻¹, along with thermal stability over six cycles. The nanocomposites developed in this study are, therefore, strong candidates for temperature sensing at the nanoscale.