Enhanced up-conversion luminescence and optical temperature sensing in graphitic C3N4 quantum dots grafted with BaWO4:Yb3+,Er3+ phosphors

Abstract

In this study, we report a novel up-conversion (UC) material from graphitic C₃N₄ (g-C₃N₄) quantum dots (QDs) grafted with BaWO₄:Yb³⁺,Er³⁺via a solvent-free thermal- and crystalline-cutting method. The g-C₃N₄/BaWO₄:Yb³⁺,Er³⁺ composite presents enhanced UC emission under 980 near-infrared (NIR) light compared to that of BaWO₄:Yb³⁺,Er³⁺, which is attributed to the efficient energy capture of the non-radiative transitions from the higher excited energy level of [²F_7/2, ¹B(¹T₂)] to the lower energy level of [²F_7/2, ¹E(¹T₂)] assisted by the energy level of the g-C₃N₄ QDs. We investigate the thermal properties of the two green UC emissions with coupled levels of ²H_11/2/⁴I_15/2 and ⁴S_3/2/⁴I_15/2 for Er³⁺ between 293 and 393 K as an optical thermometry sensor via the fluorescence intensity ratio technique. Such composite materials with enhanced UC luminescence can be used in the field of self-calibrated and highly sensitive optical thermometers to monitor the temperature changes with a maximum relative sensitivity of 1.47% K⁻¹ at 393 K. The results indicate that g-C₃N₄ QD grafted UC systems can act as promising candidates for use as optical thermometers.