Multifunctional Optical Sensing with Lanthanide-Doped Upconverting Nanomaterials: Improving Detection Performance of Temperature and Pressure in the Visible and NIR Ranges.

Temperature and pressure are fundamental physical parameters in the field of materials science, making their monitoring of utmost significance for scientists and engineers. Here, the NaSrY(MoO4)3:0.02Er3+/0.01Tm3+/0.15Yb3+ nanophosphor is developed as an optical sensor material. Under 975 nm laser excitation, the upconversion characteristics and optical detection performance of the multifunctional sensing platform of temperature and pressure (vacuum) are investigated. We have successfully developed a novel detection platform that enables optical detection of pressure (vacuum) and temperature. This platform utilizes thermally coupled levels (TCLs) and non-TCLs of Er3+ and Tm3+ to achieve ratiometric detection. The multimodal optical temperature and pressure detection based on TCLs and non-TCLs is successfully realized by using different emission bands of double emission centers, which makes it possible for self-referencing optical temperature and pressure measurement modes. These results indicate that the developed nanophosphor is a promising candidate for optical sensors, and our findings suggest potential strategies for modulating the sensor properties of luminescent materials doped with rare-earth ions.

Regulating the upconversion luminescence properties of Tm3+/Yb3+-codoped ZrScW2PO12 microparticles with a negative thermal expansion effect through thermal stimulation for optical thermometry.

Tm3+/Yb3+-codoped ZrScW2PO12 microparticles were prepared in order to solve the problems of the severe thermal quenching and unsatisfactory thermometric properties of most luminescent materials. The synthesized materials exhibit a rarely observed negative thermal expansion (NTE) effect, which was verified by in situ X-ray diffraction experiments, performed under high temperature conditions. Upon excitation with a 980 nm laser, bright blue upconversion (UC) emissions originating from Tm3+ were observed. Moreover, owing to the promoted energy transfer, cross-relaxation and non-radiative decay processes at high temperatures triggered by the NTE effect, the observed UC emissions arising from 1G4 and 3F2,3 levels show non-monotonic responses to temperature. By analysing the temperature-dependent luminescence intensity ratio of these UC emissions originating from the non-thermally coupled levels of Tm3+ (1G4 and 3F2,3), the thermometric properties of the prepared microparticles were investigated in detail. Interestingly, the maximum absolute and relative sensitivities of the synthesized compounds are 0.09 and 1.45% K-1, respectively, which are independent of Yb3+ content, but they can be manipulated by employing different sensing modes. Our results manifest that the exploitation of the NTE effect is an efficient way to control the UC luminescence features of rare earth ions and to realize high performance optical thermometry.

Pressure-Induced Remarkable Spectral Red-Shift in Mn2+ -Activated NaY9 (SiO4 )6 O2 Red-Emitting Phosphors for High-Sensitive Optical Manometry.

To settle the low sensitivity of luminescent manometers, the Mn2+ -activated NaY9 (SiO4 )6 O2 red-emitting phosphors with splendid pressure sensing performances are developed. Excited by 408 nm, the resulting products emit bright red emission originating from 4 T1 (4 G) → 6 A1 transition of Mn2+ , in which the optimal concentration of the activator ion is ≈1 mol%. Moreover, the admirable thermal stability of the developed phosphors is studied and confirmed by the temperature-dependent emission spectra, based on which the activation energy is derived to be 0.275 eV. By analyzing the pressure-dependent Raman spectra, the structural stability of the synthesized compounds at extreme conditions is verified. Furthermore, the designed phosphors exhibit remarkable spectral red-shift at elevated pressure. Especially, as pressure increases from 0.75 to 7.16 GPa, the emission band centroid shifts from 617.2 to 663.4 nm, resulting in a high sensitivity (dλ/dP) of 7.00 nm GPa-1 , whereas the full width at half maximum (FWHM) increases from 83.0 to 110.6 nm, leading to the ultra-high sensitivity (dFWHM/dP) of 10.13 nm GPa-1 . These achievements manifest that the designed red-emitting phosphors are appropriate for ultrasensitive optical manometry. More importantly, the developed manometer is a current global leader in sensitivity, when operating in the band-width mode, that is, FWHM.

The developments of cyan emitting phosphors to fulfill the cyan emission gap of white-LEDs.

Future generations of solid-state lighting (SSL) will prioritize the development of innovative luminescent materials with superior characteristics. The phosphors converted into white light-emitting diodes (white LEDs) often have a blue-green cavity. Cyan-emitting phosphor fills the spectral gap and produces "full-visible-spectrum lighting." Full-visible spectrum lighting is beneficial for several purposes, such as light therapy, plant growth, and promoting an active and healthy lifestyle. The design of cyan garnet-type phosphors, like Ca2LuHf2Al3O12 (CLHAO), has recently been the subject of interest. This review study reports a useful cyan-emitting phosphor based on CLHAO composition with a garnet structure to have a cyan-to-green emitting color with good energy transfer. It could be employed as cyan filler in warm-white LED manufacturing. Due to its stability, ability to dope with various ions suitable for their desired qualities, and ease of synthesis, this garnet-like compound is a great host material for rare-earth ions. The development of CLHAO cyan-emitting phosphors has exceptionally high luminescence, resulting in high CRI and warm-white LEDs, making them a viable desire for LED manufacturing. The development of CLHAO cyan-emitting phosphors with diverse synthesis techniques, along with their properties and applications in white LEDs, are extensively covered in this review paper.

Ultralow pressure sensing and luminescence thermometry based on the emissions of Er3+/Yb3+ codoped Y2Mo4O15 phosphors.

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature.

Mechanoluminescence and Photoluminescence Heterojunction for Superior Multimode Sensing Platform of Friction, Force, Pressure, and Temperature in Fibers and 3D-Printed Polymers.

Endowing a single material with various types of luminescence, that is, exhibiting a simultaneous optical response to different stimuli, is vital in various fields. A photoluminescence (PL)- and mechanoluminescence (ML)-based multifunctional sensing platform is built by combining heterojunctioned ZnS/CaZnOS:Mn2+ mechano-photonic materials using a 3D-printing technique and fiber spinning. ML-active particles are embedded in micrometer-sized cellulose fibers for flexible optical devices capable of emitting light driven by mechanical force. Individually modified 3D-printed hard units that exhibit intense ML in response to mechanical deformation, such as impact and friction, are also fabricated. Importantly, they also allow low-pressure sensing up to ≈100 bar, a range previously inaccessible by any other optical sensing technique. Moreover, the developed optical manometer based on the PL of the materials demonstrates a superior high-pressure sensitivity of ≈6.20 nm GPa-1 . Using this sensing platform, four modes of temperature detection can be achieved: excitation-band spectral shifts, emission-band spectral shifts, bandwidth broadening, and lifetime shortening. This work supports the possibility of mass production of ML-active mechanical and optoelectronic parts integrated with scientific and industrial tools and apparatus.

Noncentrosymmetric Lanthanide-Based MOF Materials Exhibiting Strong SHG Activity and NIR Luminescence of Er3+: Application in Nonlinear Optical Thermometry.

Optically active luminescent materials based on lanthanide ions attract significant attention due to their unique spectroscopic properties, nonlinear optical activity, and the possibility of application as contactless sensors. Lanthanide metal-organic frameworks (Ln-MOFs) that exhibit strong second-harmonic generation (SHG) and are optically active in the NIR region are unexpectedly underrepresented. Moreover, such Ln-MOFs require ligands that are chiral and/or need multistep synthetic procedures. Here, we show that the NIR pulsed laser irradiation of the noncentrosymmetric, isostructural Ln-MOF materials (MOF-Er3+ (1) and codoped MOF-Yb3+/Er3+ (2)) that are constructed from simple, achiral organic substrates in a one-step procedure results in strong and tunable SHG activity. The SHG signals could be easily collected, exciting the materials in a broad NIR spectral range, from ≈800 to 1500 nm, resulting in the intense color of emission, observed in the entire visible spectral region. Moreover, upon excitation in the range of ≈900 to 1025 nm, the materials also exhibit the NIR luminescence of Er3+ ions, centered at ≈1550 nm. The use of a 975 nm pulse excitation allows simultaneous observations of the conventional NIR emission of Er3+ and the SHG signal, altogether tuned by the composition of the Ln-MOF materials. Taking the benefits of different thermal responses of the mentioned effects, we have developed a nonlinear optical thermometer based on lanthanide-MOF materials. In this system, the SHG signal decreases with temperature, whereas the NIR emission band of Er3+ slightly broadens, allowing ratiometric (Er3+ NIR 1550 nm/SHG 488 nm) temperature monitoring. Our study provides a groundwork for the rational design of readily available and self-monitoring NLO-active Ln-MOFs with the desired optical and electronic properties.

Ratiometric Upconversion Temperature Sensor Based on Cellulose Fibers Modified with Yttrium Fluoride Nanoparticles.

In this study, an optical thermometer based on regenerated cellulose fibers modified with YF3: 20% Yb3+, 2% Er3+ nanoparticles was developed. The presented sensor was fabricated by introducing YF3 nanoparticles into cellulose fibers during their formation by the so-called Lyocell process using N-methylmorpholine N-oxide as a direct solvent of cellulose. Under near-infrared excitation, the applied nanoparticles exhibited thermosensitive upconversion emission, which originated from the thermally coupled levels of Er3+ ions. The combination of cellulose fibers with upconversion nanoparticles resulted in a flexible thermometer that is resistant to environmental and electromagnetic interferences and allows precise and repeatable temperature measurements in the range of 298-362 K. The obtained fibers were used to produce a fabric that was successfully applied to determine human skin temperature, demonstrating its application potential in the field of wearable health monitoring devices and providing a promising alternative to thermometers based on conductive materials that are sensitive to electromagnetic fields.

Generation of Pure Green Up-Conversion Luminescence in Er3+ Doped and Yb3+-Er3+ Co-Doped YVO4 Nanomaterials under 785 and 975 nm Excitation.

Materials that generate pure, single-color emission are desirable in the development and manufacturing of modern optoelectronic devices. This work shows the possibility of generating pure, green up-conversion luminescence upon the excitation of Er3+-doped nanomaterials with a 785 nm NIR laser. The up-converting inorganic nanoluminophores YVO4: Er3+ and YVO4: Yb3+ and Er3+ were obtained using a hydrothermal method and subsequent calcination. The synthesized vanadate nanomaterials had a tetragonal structure and crystallized in the form of nearly spherical nanoparticles. Up-conversion emission spectra of the nanomaterials were measured using laser light sources with λex = 785 and 975 nm. Importantly, under the influence of the mentioned laser irradiation, the as-prepared samples exhibited bright green up-conversion luminescence that was visible to the naked eye. Depending on the dopant ions used and the selected excitation wavelengths, two (green) or three (green and red) bands originating from erbium ions appeared in the emission spectra. In this way, by changing the UC mechanisms, pure green luminescence of the material can be obtained. The proposed strategy, in combination with various single-doped UC nanomaterials activated with Er3+, might be beneficial for modern optoelectronics, such as light-emitting diodes with a rich color gamut for back-light display applications.

Optically active plasmonic cellulose fibers based on Au nanorods for SERS applications.

Cellulose might be a promising material for surface-enhanced Raman scattering (SERS) substrates due to its wide availability, low cost, ease of fabrication, high flexibility and low optical activity. This work shows, for the first time development of the cellulose-based substrate, that owes its SERS activity to the presence of gold nanorods in its internal structure, and not only on the surface, as it is shown elsewhere, thus ensuring superior stability of the obtained material. This flexible cellulose-based substrate exhibiting plasmonic activity, provide easy and reproducible detection of different analytes via SERS technique. The substrate was prepared by introduction of gold nanorods into the cellulose fibers matrix using an eco-friendly process based on N-Methylmorpholine-N-Oxide. Au-modified cellulose fibers were used for the detection of p-Mercaptobenzoic acid and Bovine Serum Albumin by the SERS method. The obtained results show that this substrate offers large signal enhancement of 6-orders of magnitude, and high signal reproducibility with a relative standard deviation of 8.3%. Additionally, washing tests (90 °C, 20 h) showed superior stability of the as prepared plasmonic fibers, thus proving the good reusability of the substrates and the long shelf life.

NIR emission of lanthanides for ultrasensitive luminescence manometry-Er3+-activated optical sensor of high pressure.

Pressure is an important physical parameter and hence its monitoring is very important for different industrial and scientific applications. Although commonly used luminescent pressure sensors (ruby-Al2O3:Cr3+ and SrB4O7:Sm2+) allow optical monitoring of pressure in compressed systems (usually in a diamond anvil cell; DAC), their detection resolution is limited by sensitivity, i.e., pressure response in a form of the detected spectral shift. Here we report, a breakthrough in optical pressure sensing by developing an ultra-sensitive NIR pressure sensor (dλ/dP = 1.766 nm GPa-1). This luminescent manometer is based on the optically active YVO4:Yb3+-Er3+ phosphor material which exhibits the largest spectral shift as a function of pressure compared to other luminescent pressure gauges reported elsewhere. In addition, thanks to the locations of excitation and emission in the NIR range, the developed optical manometer allows high-pressure measurements (without spectral overlapping/interferences) of various luminescent organic and inorganic materials, which are typically excited and can emit in the UV-vis spectral ranges.

Improving performance of luminescent nanothermometers based on non-thermally and thermally coupled levels of lanthanides by modulating laser power.

This work sheds light on the pump power impact on the performance of luminescent thermometers, which is often underestimated by researchers. An up-converting, inorganic nanoluminophore, YVO4:Yb3+,Er3+ (nanothermometer) was synthesized using the hydrothermal method and a subsequent calcination. This nanomaterial appears as a white powder composed of small nanoparticles (≈20 nm), exhibiting a very intense, green upconverted luminescence (λex = 975 nm), visible to the naked eye. Its emission spectrum consists of four Er3+ bands (500-850 nm) and one Yb3+ band (>900 nm). The obtained compound exhibits temperature-dependent luminescence properties, hence it is used as an optical nanosensor of temperature. The determined band intensity ratios of the non-thermally coupled levels (non-TCLs) of Yb3+/Er3+ and thermally coupled levels (TCLs) of Er3+ are correlated with temperature, and they are used for ratiometric sensing of temperature. The effects of the pump (NIR laser) power on the luminescence properties of the material, including band intensity ratios, absolute and relative sensitivities and temperature resolution are analysed. It was pointed out that the applied laser power has a huge impact on the values of the aforementioned thermometric parameters, and manipulating the laser power can significantly improve the performance of optical nanothermometers.

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

Lanthanide-based luminescent nanothermometers play a crucial role in optical temperature determination. However, because of the strong thermal quenching of the luminescence, as well as the deterioration of their sensitivity and resolution with temperature elevation, they can operate in a relatively low-temperature range, usually from cryogenic to ≈800 K. In this work, we show how to overcome these limitations and monitor very high-temperature values, with high sensitivity (≈2.1% K-1) and good thermal resolution (≈1.4 K) at around 1000 K. As an optical probe of temperature, we chose upconverting Yb3+-Tm3+ codoped YVO4 nanoparticles. For ratiometric sensing in the low-temperature range, we used the relative intensities of the Tm3+ emissions associated with the 3F2,3 and 3H4 thermally coupled levels, that is, 3F2,3 → 3H6/3H4 → 3H6 (700/800 nm) band intensity ratio. In order to improve sensitivity and resolution in the high-temperature range, we used the 940/800 nm band intensity ratio of the nonthermally coupled levels of Yb3+ (2F5/2 → 2F7/2) and Tm3+ (3H4 → 3H6). These NIR bands are very intense, even at extreme temperature values, and their intensity ratio changes significantly, allowing accurate temperature sensing with high thermal and spatial resolutions. The results presented in this work may be particularly important for industrial applications, such as metallurgy, catalysis, high-temperature synthesis, materials processing and engineering, and so forth, which require rapid, contactless temperature monitoring at extreme conditions.

Lanthanide Upconverted Luminescence for Simultaneous Contactless Optical Thermometry and Manometry-Sensing under Extreme Conditions of Pressure and Temperature.

The growing interest in the miniaturization of various devices and conducting experiments under extreme conditions of pressure and temperature causes the need for the development of small, contactless, precise, and accurate optical sensors without any electrical connections. In this work, YF3:Yb3+-Er3+ upconverting microparticles are used as a bifunctional luminescence sensor for simultaneous temperature and pressure measurements. Different changes in the properties of Er3+ green and red upconverted luminescence, after excitation of Yb3+ ions in the near-infrared at ∼975 nm, are used to calibrate pressure and/or temperature inside the hydrostatic chamber of a diamond anvil cell (DAC). For temperature sensing, changes in the relative intensities of the Er3+ green upconverted luminescence of 2H11/2 and 4S3/2 thermally coupled multiplets to the 4I15/2 ground state, whose relative populations follow a Boltzmann distribution, are calibrated. For pressure sensing, the spectral shift of the Er3+ upconverted red emission peak at ∼665 nm, between the Stark sublevels of the 4F9/2 → 4I15/2 transition, is used. Experiments performed under simultaneous extreme conditions of pressure, up to ∼8 GPa, and temperature, up to ∼473 K, confirm the possibility of remote optical pressure and temperature sensing.

Surface Modification of Luminescent LnIII Fluoride Core-Shell Nanoparticles with Acetylsalicylic acid (Aspirin): Synthesis, Spectroscopic and in Vitro Hemocompatibility Studies.

Luminescent lanthanide fluoride core-shell (LaF3 :Tb3+ ,Ce3+ @SiO2 -NH2 ) nanoparticles, with acetylsalicylic acid (aspirin) coated on the surface have been obtained. The synthesized products, which combine the potential located in the silica shell with the luminescent activity of the core, were characterized in detail with the use of luminescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) methods. The in vitro effects of the modified luminescent nanoparticles on human red blood cell (RBC) membrane permeability, RBC shape, and sedimentation rate were investigated to assess the hemocompatibility of the obtained compounds. This study demonstrates that LaF3 : Tb3+ 5 %, Ce3+ 10 %@SiO2 -NH2 nanoparticles with acetylsalicylic acid (aspirin) coated on the surface are very good precursors for multifunctional drug-delivery systems or bio-imaging probes that can be used safely in potential biomedical applications.

3,5-Dihydroxy Benzoic Acid-Capped CaF2:Tb3+ Nanocrystals as Luminescent Probes for the WO4 2- Ion in Aqueous Solution.

We report a facile and effective luminescence method for the determination of the WO4 2- ion in aqueous medium at initial pH = 6.3. This is achieved using 3,5-dihydroxybenzoic acid-capped CaF2:Tb3+ (5%) nanocrystals (NCs) as a luminescent probe. This is accomplished based on the energy transfer luminescence from the WO4 2- ion to the Tb3+ ion in small-size CaF2:Tb3+ NCs. Hydroxyl groups on the surface ligand helps in binding the tungstate ion to the surface of the NCs. With the gradual addition of the WO4 2- ion, the intensity of the Tb3+ excitation and emission spectra significantly increased. The linear range of the detection was from 1 to 10 µM for the WO4 2- ion (R 2 = 0.99). The calculated detection limit was 0.4 µM (by applying the 3σ/K criterion).

UV-Vis-NIR absorption spectra of lanthanide oxides and fluorides.

The absorption characteristics of lanthanide-based functional materials are of key importance for many scientists and engineers, e.g. in luminescence studies, bioimaging, optical heating/cooling, Raman spectroscopy, and industrial applications such as new light sources, optical sensors, labeling and tracing techniques, etc. Here we show the absorption spectra of solid, optically active lanthanide fluorides (CeF3, PrF3, NdF3, SmF3, EuF3, GdF3, TbF3, DyF3, HoF3, ErF3, TmF3, and YbF3) and oxides (CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3), measured in the UV-Vis-NIR range, from 200 to 2500 nm. The spectra were measured in diffused-reflectance mode using a spherical integrator. We assigned energy levels (2S+1LJ) of lanthanide ions(iii), i.e. intraconfigurational 4f-4f transitions to the observed absorption bands. In order to clearly distinguish the 4f → 4f transitions, we also pointed out other absorption bands commonly observed in the measured spectra, such as intrinsic absorption of the matrices, interconfigurational 4f → 5d and charge transfer transitions, artificial bands from absorbed water (present in most materials) and a quartz holder.

Gold nanorods as a high-pressure sensor of phase transitions and refractive-index gauge.

Gold nanorods (Au NRs), nanospheres and other nanoparticles display numerous superior physicochemical properties, such as resistance to oxidation and aggressive agents, strong enhancement of local electric field and a high absorption coefficient in the visible and near-infrared (NIR) range. The absorption peaks of surface plasmon resonance (SPR) in Au NRs are highly sensitive to their surrounding medium and to its refractive index (RI) changes. However, no applications of NRs for detecting phase transitions have been reported. Here, we show that Au NRs effectively detect phase transitions of compressed compounds, liquid and solid, by measuring their RI. Owing to the direct interaction of the NRs with their surrounding medium, its subtle RI changes can be observed by the use of high-pressure absorption vis-NIR spectroscopy. We have applied a Au NR-based sensor in a diamond anvil cell (DAC) for monitoring the phase transitions of compressed water, its freezing to ice VI and at the subsequent solid-solid phase transition to ice VII, and the monotonic compression and solid-solid phase transitions in urea and thiourea.

Upconverting Lanthanide Fluoride Core@Shell Nanorods for Luminescent Thermometry in the First and Second Biological Windows: ß-NaYF4:Yb3+- Er3+@SiO2 Temperature Sensor.

Upconverting core@shell type ß-NaYF4:Yb3+-Er3+@SiO2 nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λex = 975 nm), i.e., upconversion luminescence of Er3+ and down-shifting emission of Yb3+, located in the first (I-BW) and the second (II-BW) biological windows of the spectral range, respectively. The intensity ratios of the emission bands of Er3+ and Yb3+ observed in the vis-near-infrared (NIR) range monotonously change with temperature, i.e., the thermalized Er3+ levels (2H11/2 → 4I15/2/4S3/2 → 4I15/2) and the nonthermally coupled Yb3+/Er3+ levels (2F5/2 → 2F7/2/4I9/2 → 4I15/2 or 4F9/2 → 4I15/2). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and second-order polynomial fits for temperature-sensing purposes, i.e., Er3+ 525/545 nm (max Sr = 1.31% K-1) and Yb3+/Er3+ 1010/810 nm (1.64% K-1) or 1010/660 nm (0.96% K-1). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb3+/Er3+ bands, vs. the typically used Er3+ 525/545 nm band ratio, i.e., better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range vis-NIR optical, contactless sensors of temperature.

Optical Pressure Sensor Based on the Emission and Excitation Band Width (fwhm) and Luminescence Shift of Ce3+-Doped Fluorapatite-High-Pressure Sensing.

A novel, contactless optical sensor of pressure based on the luminescence red-shift and bandwidth (full width at half-maximum, fwhm) of the Ce3+-doped fluorapatite-Y6Ba4(SiO4)6F2 powder has been successfully synthesized via a facile solid-state method. The obtained material exhibits a bright blue emission under UV light excitation. It was characterized using powder X-ray diffraction, scanning electron microscopy and luminescence spectroscopy, including high-pressure measurements of excitation and emission spectra, up to above ∼30 GPa. Compression of the material resulted in a significant red-shift of the allowed 4f → 5d and 5d → 4f transitions of Ce3+ in the excitation and emission spectra, respectively. The pressure-induced monotonic shift of the emission band, as well as changes in the excitation/emission band widths, have been correlated with pressure for sensing purposes. The material exhibits a high pressure sensitivity (dλ/d P ≈ 0.63 nm/GPa) and outstanding signal intensity at high-pressure conditions (∼90% of the initial intensity at around 20 GPa) with minimal pressure-induced quenching of luminescence.