Enhanced upconversion luminescence of BiOCl:Yb3+,Er3+ nanosheets via carbon dot modification and their optical temperature sensing

Abstract

Abstract: This study aimed to report a new strategy for efficient upconversion (UC) enhancement of rare earth doped nanomaterials via modifying carbon dots (CDs) on semiconducting nanosheets. CDs-modified Er3+/Yb3+ co-doped BiOCl nanosheets were synthesized via a facile hydrothermal and subsequent heat treatment method for the first time. Under excitation of 980 nm laser, the CDs/BiOCl:Yb3+, Er3+ composites could present up to ten times the improvement in UC emission intensity and the extended fluorescence lifetime simultaneously. Experimental results indicate that the surface passivation and the increased photocarriers separation efficiency of Er3+/Yb3+ co-doped BiOCl nanosheets by CDs modification synergistically enhance the UC photoluminescence of Er3+ ions by extending its decay time of excited state levels. Moreover, such composite materials with enhanced UC luminescence can be used as highly sensitive optical thermometers using the fluorescence intensity ratio technique in which green emissions are suitable for temperatures below 293K with the maximum relative sensitivity of 1.35% K-1 and red emissions are appropriate for temperatures above 573K with the maximum sensitivity of 0.32% K−1 in the experimental range. This study not only opened new perspectives for the enhanced UC luminescence but also paved way for the design and fabrication of high-efficiency UC nanocrystals for potential applications in optical temperature sensing. Keywords: CDs; BiOCl; upconversion; photocarriers separation; thermometry sensor