Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Abstract

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF4:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H2O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K−1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

Special Issue: Rare earth luminescent materials

“…Lanthanide-doped inorganic upconversion nanoparticles (UCNPs) excitable with NIR light sources are regarded as promising alternatives with which to circumvent background fluorescence and stray light. In this special issue, An and coworkers report a novel one-step approach for synthesizing hollow structured UCNPs without a template 18 . These hollow UCNPs could act as stable self-referenced ratiometric luminescent thermometers over a broad temperature range.…”

Energy Gap Linear Superposition of Thermally Coupled Levels toward Enhanced Relative Sensitivity of Ratiometric Thermometry

“…An accurate temperature measurement is of great significance and triggers a great demand for versatile thermometers. − Thereinto, ratiometric luminescence thermometry (RLT) has attracted considerable attention by virtues of non-invasive, fast response, high precision, and substantial electromagnetic interference resistance. , Generally, conventional RLT is performed by decoding the functional relationship between the temperature and fluorescence intensity ratio (FIR) of two emission bands detonated by thermally coupled levels (TCLs) of the luminescence centers . To evaluate the performance of optical thermometry, the relative sensitivity ( S R ) is proposed and expressed as a percentage change per temperature, reflecting the thermally induced relative change of FIR .…”

“…23 On the basis of the analysis above, we introduced multipairs of TCLs for RLT. The new FIR (FIR′) can be executed by multiplying the FIRs of conventional TCLs as follows: (5) As a result, corresponding S R ′ precisely becomes the linear superposition of conventional S R values of involved TCLs. G 5/2 → 4 I 11/2 , 4 F 7/2 → 4 I 9/2 , 4 F 5/2 → 4 I 9/2 , and 4 F 3/2 → 4 I 9/2 transitions, respectively.…”

NaBiF4-based hollow upconversion nanoparticles for temperature sensing

“…Now, writing in this issue of Light: Science & Applications , Prof. Hongjie Zhang and colleagues at the State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, China report a one-step template-free method for the synthesis of NaBiF 4 :Yb,Er hollow UCNPs 14 . Moreover, they achieved controllable tuning of the cavity size in the nanoparticles.…”