Lanthanide-Doped Bi₂SiO₅@SiO₂ Core–Shell Upconverting Nanoparticles for Stable Ratiometric Optical Thermometry

Abstract

The development of nanomaterials with high sensitivity to external stimuli such as temperature is critical to investigate the driving force of not only biological processes but also catalytic mechanisms in extreme environments. However, the instability of nano-objects at high temperatures and different environments is a serious drawback limiting often their real use. This is particularly severe in the case of bismuth-based compounds, making the development of highly stable bismuth-based nanosystems a challenge. Here, we report the synthesis of uniform crystalline lanthanide-doped Bi 2 SiO 5 nanoparticles into a silica shell of a controlled thickness (Bi 2 SiO 5 :Ln@SiO 2 ) for the design of a reliable ratiometric optical thermometer stable at high temperatures and extreme acid environments. The fine control of the SiO 2 shell thickness is modeled based on a theoretical and experimental approach. The formation of the Bi 2 SiO 5 single phase is triggered by the local reactivity between Bi 2 O 3 and SiO 2 in the Bi 2 O 3 @SiO 2 system, leading to a double-layered Bi 2 SiO 5 @SiO 2 hollow nanosystem. The potential of the Bi 2 SiO 5 :Ln@SiO 2 nanosystem as a ratiometric nanothermometer is demonstrated for the upconverting Yb−Er couple. The performances were evaluated in the wide range of linearity of the Boltzmann law (280−800 K) showing suitable values of relative sensitivity, temperature uncertainty, and repeatability (R > 99%) not only for biological applications but also to probe the temperature in extreme environments. In fact, the strategy results in an acid-inert thermal probe up to pH < 1 overcoming the weakness of bismuthbased materials to acid environments with promising properties for in situ thermometry of catalytic reactions.

Defect induced “super mop” like behaviour of Eu3+-doped hierarchical Bi2SiO5nanoparticles for improved catalytic and adsorptive behaviour

“…Such an observation was earlier reported by Back et al 20 The peaks in PXRD for the other three materials (Eu 0.5 -BSO, Eu 1 -BSO, and Eu 2 -BSO) obtained after 10 h also correspond to pure monoclinic BSO without the presence of any impurity phase (Fig. 1).…”

“…The exact origin of this peak is debatable as this peak is reported to appear for tetragonal BSO with I4/mmm symmetry only upon heteroatom doping. 20,25 Moreover, this is also present in the standard pattern of both monoclinic and orthorhombic phases of BSO. As in our case, this peak appeared for undoped BSO, and we believe that this indicates the formation of monoclinic/orthorhombic phases.…”

“…Bi 2 SiO 5 (BSO) is one of the emerging lead free substitutes of ferroelectric as well as luminescent probes in thermometry. [18][19][20][21][22][23][24] In particular, BSO is a potential material because of its layered structure made up by intergrowth of the [SiO 3 ] 2À pyroxene layer and [Bi 2 O 2 ] 2+ layer. The [Bi 2 O 2 ] 2+ layer is structurally built up of an oxygen bound square pyramidal layer with Bi 3+ ions sitting at the top of the pyramid.…”

Primary Luminescent Nanothermometers for Temperature Measurements Reliability Assessment

“…[ 8,33,64–69 ] Except for the semiconductor nanoparticles, that are based on the temperature‐dependent emission peak position (Varshni's Law), [ 8,64 ] all these primary thermometers are based on the intensity ratio between two thermally coupled levels (Boltzmann statistics), such as, 7 F 0 and 7 F 2 of Eu 3+ , [ 62 ] 5 D 4 of Tb 3+ and the first excited triplet of tfac (tfac = 1,1,1‐trifluoro‐2,4‐pentanedione) ligand, [ 66 ] and 2 H 11/2 and 4 S 3/2 of Er 3+ . [ 33,67–69 ] In 2017, Balabhadra et al proposed a straightforward method to predict the temperature calibration curve of any upconverting thermometer based on two thermally coupled electronic levels independently of the medium, using Yb 3+ /Er 3+ ‐doped SrF 2 nanoparticles as an illustrative example. The 2 H 11/2 → 4 I 15/2 ( I H ) and 4 S 3/2 → 4 I 15/2 ( I S ) emission bands intensities allowed to calculate the absolute temperature, T , by [ 33 ] where k B is the Boltzmann constant, Δ E is the energy gap between the barycenters of the 2 H 11/2 and 4 S 3/2 levels, and Δ = I H / I S is the thermometric parameter with Δ 0 being the value at the temperature T 0 (see Supporting Information for the calculus of Δ E and Δ 0 ).…”

mOptical Sensing for the Internet of Things: A Smartphone‐Controlled Platform for Temperature Monitoring

“…[ 47,53–58 ] The solution lies in primary thermometers, characterized by a well‐established state‐equation that directly relates a particular measured value to the absolute temperature without the need for calibration. So far, only a few primary luminescent thermometers have been reported, [ 43,53,58–65 ] most of which based on the intensity ratio between two thermally coupled electronic levels, for instance, the Er 3+ 2 H 11/2 and 4 S 3/2 levels. In this case, the thermometric parameter is based exclusively upon the validity of the Boltzmann distribution.…”