Luminescent Nd³⁺‐Based Microresonators Working as Optical Vacuum Sensors

Abstract

this technology is the requirement of precise and reliable vacuum measurements. The advances in the field come along with harder requirements to meet in terms of precision and miniaturization of the sensors. [3] Vacuum gauges currently used are based on mechanical deformation, [4,5] thermal conductivity [6-8] such as Pirani, [9] thermocouple or thermistor gauges; ionization [10,11] and spinning rotations. [12] All these approaches are more or less suitable depending on the pressure range of the measurements. But for all ranges, the vacuum gauges based on the previous parameters have an uncertainty from around 1% to 20%. Another approach to measure vacuum that has been barely investigated is the use of optical sensor. Up to date, the only researches following this approach were based on heterodyne [13,14] and optical fiber interferometry, [15,16] resonance effects [17-19] or magneto-optical trapping. [2] Furthermore, luminescent materials play an important role as phosphors, contrast agent, labels, optical heaters/coolers, temperature and pressure sensors, etc. [20,21] In the field of luminescent materials, the lanthanide based organic and inorganic compounds are of special importance. This is mostly due to their favorable optical properties, such as multicolor emission and up-conversion luminescence, narrow absorption and emission bands, large Stokes shift, long radiative lifetimes, etc. [22-24] Recently, in our previous publication, [21] we showed for the first time the possibility of converting luminescence thermometer into the optical vacuum sensor. To present this Glass microspheres embedded with Nd 3+-doped nanoperovskites based on yttrium orthoaluminate are synthesized and used as optical vacuum sensor. Under 532 nm excitation, the microspheres show two emission bands centered at 820 and 890 nm, corresponding to the 2 H 9/2 , 4 F 5/2 → 4 I 9/2 and 4 F 3/2 → 4 I 9/2 transitions. When the microspheres are heated by laser excitation in air (ambient conditions), the positions of the Stark level transitions shift toward red or blue spectral regions. Additionally, the full width at half maximum of these peaks increases. Furthermore, due to the specific geometry of the microspheres, it is possible to trap the emitted light inside the microsphere resonator, in the form of whispering-gallery-modes (WGM). When the microspheres are heated, these resonant modes present higher shifts toward lower energies than those for the Stark levels. As pressure decreases, the thermal exchange (convection process) between the microsphere and the surrounding air molecules decreases, which leads to an increase on the temperature of the microsphere. Based on this effect, the response of the WGM spectral positions as a function of pressure level is used to calibrate the luminescent microspheres as optical vacuum sensors. Relative sensitivity and limit of detection are obtained and compared with other optical vacuum sensors.

Luminescent Nanothermometer Operating at Very High Temperature—Sensing up to 1000 K with Upconverting Nanoparticles (Yb3+/Tm3+)

“…On the other hand, the use of upconverting nanomaterials is commonly proposed for biological applications (subcutaneous sensing) because of their small size and the use of NIR laser as an excitation source, eliminating harmful UV radiation. − However, nanomaterials exhibiting UC phenomena, and excited in the NIR range, are also beneficial in industrial applications. This is because they allow high-spatial resolution of temperature sensing, as well as they do not need a high-energy excitation source, which can cause other undesired effects, such as uncontrolled polymerization during catalytic processes or additional heating. ,,− It is worth noting about novel application of lanthanide-based luminescent thermometers in optical vacuum sensing, that is, conversion of luminescent thermometers into low-pressure sensors, utilizing the effect of laser-induced heating of the materials, which is enhanced under vacuum conditions. , …”

Vacuum-Assisted Strong Luminescence Thermal Enhancement in NaYF4:Ho3+/Yb3+ Upconverting Nanocrystals: A Conclusive Evidence for the Effect of Water Desorption

“…The intensity variations of the green emission, Yb 3+ emission, and 5 I 6 → 5 I 8 emission with temperature changes in heating–cooling processes in air and in vacuum are depicted in Figure b and d, respectively. It can be seen from Figure d that the intensities of three emissions will be enhanced as soon as the vacuum is pumped at 300 K. This observation should be attributed to quenchers’ desorption rather than laser-induced sample heating enhanced under vacuum conditions. − On the one hand, the excitation power density used in the experiment is low enough that there should be no obvious thermal effect (it is about 2 orders of magnitude smaller than the lowest excitation power density reported in the literature). On the other hand, the thermal effect caused by laser-induced heating should be a relatively slow process, while the observed luminescence enhancement almost takes place with vacuum pumping at once.…”

Dual-mode optical ratiometric thermometry using Pr3+-doped NaSrGd(MoO4)3 phosphors with tunable sensitivity

“…The temperature uncertainty ( δT ) using luminescence thermometry can be calculated using the equation as follows: 47,48 where δ FIR is the resolution limit or relative uncertainty of the thermometric parameter, i.e. , the smallest change in ratio that can be observed experimentally.…”

“…The temperature uncertainty (δT ) using luminescence thermometry can be calculated using the equation as follows: 47,48 δT ¼…”