Optimizing optical thermometry with tri-doped Ba2GdV3O11 phosphors: Ratiometric and fluorescence lifetime analysis.

Optical sensor technology has undergone a transformative evolution with the advent of fluorescence ratio techniques (FIR) and fluorescence lifetime (FL) strategies, revolutionizing precision, performance, and reliability. This study delves into the synthesis of Ba2GdV3O11 phosphors doped with Ho3+/Nd3+, Er3+, and Yb3+, employing the sol-gel method for upconverting material fabrication. A thorough investigation into the structural, morphological, and optical properties of the synthesized phosphors is conducted. Excitation at 980 nm unveils upconversion (UC) emissions across green and red spectra. The intensities of the observed emission bands for Ho3+, Nd3+, and Er3+ demonstrate significant sensitivity to fluctuations in temperature. Temperature sensing relies on the 4S3/2 and 2H11/2 upconversion emissions bands, in addition to the emission lifetimes at 4S3/2. Enhanced thermal sensitivity values are attained, reaching up to 1.03 % K-1 and 1.07 % K-1 using the FIR strategy, and up to 0.146 % K-1 and 0.47 % K-1 with the FL strategy for Ho3+/Er3+/Yb3+ and Nd3+/Er3+/Yb3+ tri-doped Ba2GdV3O11 phosphors, respectively. Furthermore, the studied phosphors exhibit remarkable precision in detecting minute temperature changes (0.3 K), positioning them as promising candidates for precise temperature sensing. This study pioneers innovative methodologies to advance optical thermometry techniques, offering promising prospects for scientific and industrial applications reliant on precise optical temperature sensing.

Filtering Organized 3D Point Clouds for Bin Picking Applications.

In robotic bin-picking applications, autonomous robot action is guided by a perception system integrated with the robot. Unfortunately, many perception systems output data contaminated by spurious points that have no correspondence to the real physical objects. Such spurious points in 3D data are the outliers that may spoil obstacle avoidance planning executed by the robot controller and impede the segmentation of individual parts in the bin. Thus, they need to be removed. Many outlier removal procedures have been proposed that work very well on unorganized 3D point clouds acquired for different, mostly outdoor, scenarios, but these usually do not transfer well to the manufacturing domain. This paper presents a new filtering technique specifically designed to deal with the organized 3D point cloud acquired from a cluttered scene, which is typical for a bin-picking task. The new procedure was tested on six different datasets (bins filled with different parts) and its performance was compared with the generic statistical outlier removal procedure. The new method outperforms the general procedure in terms of filtering efficacy, especially on datasets heavily contaminated by numerous outliers.

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.

Enhancing thermometric efficiency: a wavelength excitation analysis in LiSrGdW3O12:Tb3+ for superior single band ratiometric (SBR) thermometry.

This study delves into the Single Band Ratiometric (SBR) method for luminescence thermometry, specifically employing Tb3+-doped LiSrGdW3O12 (LSGW) as a novel phosphor. The prepared samples crystallize with the tetragonal scheelite structure, with the optimal Tb3+ concentration pinpointed at 0.3Tb3+ ions. When stimulated at diverse wavelengths exhibit luminescence characterized by varying heat dependencies. By utilizing two Fluorescence Intensity Ratio (FIR) parameters for the 544 nm green emission, firstly excited at 405 nm and 488 nm, and then at 405 nm and 379 nm, the Sr relative thermal sensitivity of the luminescent thermometer peaks at 3.56% K-1 and 4.21% K-1, respectively, within the temperature range of 290-440 K. The temperature resolution (δT) of the luminescent thermometer is calculated to be δT1 = 0.68 K and δT2 = 0.75 K for T = 290 K, respectively. These outcomes underscore the applicability of Tb3+ ions for SBR thermometry, emphasizing the impact of the excitation wavelength on the thermal sensitivity. The study lays the groundwork for developing highly sensitive temperature probes by elucidating the interplay of material properties and physical processes.

The dual-model up/down-conversion green luminescence of NaSrGd(MoO4)3: Er3+ and its application for temperature sensing.

Er3+-doped phosphors are widely used as dual-functional optical thermometers due to their distinctive up/down-conversion luminescence and the thermally coupled energy states (2H11/2 and 4S3/2) of Er3+. The development of high-performance Er3+-activated optical thermometers is both an intriguing subject and a formidable challenge in the field. This article investigates the up/down-conversion (UC and DC) photoluminescence properties of NaSrGd(MoO4)3 (NSGM): Er3+. When excited at 375 and 975 nm, the phosphors emit peaks at 530, 550, and 657 nm, corresponding to the 2H11/2, 4S3/2, and 4F9/2 → 4I15/2 transitions of Er3+, with the 4S3/2 → 4I15/2 transition displaying the highest intensity. The optical properties are comprehensively studied through UV-visible absorption, PL spectroscopy, and PLE spectroscopy. Optimal luminescence intensity is achieved at an Er3+ concentration of 4% mol. The resulting chromatic coordinates (x, y) and high correlated color temperature (CCT) values of the doped phosphors yield thermally stable cold emissions in the green region, boasting color purities of approximately 98.76% and 80.74% for DC and UC conversion, respectively. The optical temperature sensing properties of thermally coupled energetic states are explored based on the fluorescence intensity ratio principle. NSGM: 0.04Er3+, under 375 nm light excitation, demonstrates the maximum relative sensitivity of 0.87%/K-1 at 298.15 K, spanning a wide temperature range from 298.15 to 488.15 K. Conversely, under 975 nm light excitation, NSGM: 0.04Er3+ exhibits the maximum relative sensitivity of 0.63%/K-1 over the same temperature range, with temperature uncertainty (δT) less than 0.50 K and repeatability (R) (more than 98%). These findings position this material as a promising candidate for optical thermometer applications. The optical heating capacity of the synthesised phosphor is also determined using optical thermometry results, and heat generation up to approximately 457 K is found, indicating that NSGM: 0.04Er3+ could be useful for photo-thermal therapy.

Advanced temperature sensing with Er3+/Yb3+ co-doped Ba2GdV3O11 phosphors through upconversion luminescence.

Optical thermometry is a non-contact temperature sensing technique with widespread applications. It offers precise measurements without physical contact, making it ideal for situations where contact-based methods are impractical. However, improving the accuracy of optical thermometry remains an ongoing challenge. Herein, enhancing the thermometric properties of luminescent thermometers through novel materials or strategies is crucial for developing more precise sensors. Hence, the present study focuses on the application of four-mode luminescence thermometric techniques in sol-gel synthesized Er3+/Yb3+ co-doped Ba2GdV3O11 phosphors for optical temperature sensing in the temperature range of 298-573 K. The upconversion (UC) luminescence is achieved under excitations of 980 nm or 1550 nm, resulting in bright yellow-green emission in the visible spectral range. Temperature sensing is realized by exploiting the UC emissions of 4S3/2, 2H11/2 and 4F7/2 bands, which represent intensity ratios of thermally coupled levels (TCELs) and non-thermally coupled levels (NTCELs) of Er3+/Yb3+, along with the emission lifetimes at 4S3/2. The relative sensitivity (Sr) values for TCELs exhibit a gradual decrease with rising temperature, reaching a maximum of 1.1% K-1 for 980 nm excitation and 0.86% K-1 for 1550 nm excitation at 298 K. Conversely, for NTCELs, the highest Sr value observed is 0.9% K-1 at 298 K for 1550 nm excitation. Moreover, the emission lifetimes at 4S3/2 yield notably high Sr values of up to 5.0% µs K-1 (at 425 K). Furthermore, the studied phosphors have a sub-degree thermal resolution, making them excellent materials for accurate temperature sensing. Overall, this study provides a promising new direction for the development of more precise and reliable optical thermometry techniques, which could have important implications for a range of scientific and industrial optical temperature sensing applications.

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

Owing to some special superior features, luminescence ratiometric thermometry has acquired popularity, particularly dual excitation single emission (SBR) and single excitation dual emission (FIR). Nonetheless, it remains difficult to create ratiometric thermometry that can operate in multiple modes. The integration of FIR and SBR techniques paves the way for advancements in various fields, including industrial processes, environmental monitoring, and biomedical applications, where accurate temperature measurements are crucial for optimal performance and safety. In this work, we describe a way to measure temperature based on the light-induced fluorescence of Pr3+ in NaSrGd(MoO4)3 (NSGM). The optical properties were investigated by UV-visible absorption, PL, and PLE spectroscopy. On the one hand, the emission of Pr3+ exhibits varying temperature-dependent behavior upon 450 nm excitation. Thus, a thermometer based on the FIR between the Pr3+ levels has been generated, with the highest sensitivity of approximately 0.83% K-1 over a wide temperature range of 290-440 K. Furthermore, the SBR luminescent thermometer was evaluated in the same temperature range. The effect of the Pr3+ concentration on red-emitting SBR luminescent thermometers was investigated in detail. The Sa and Sr values gradually increase, with the Pr3+ content reaching a maximum Sr value of 2.4% K-1 at 413 K for the NSGM:10% Pr3+ phosphor. These results show that Pr3+ ions have the potential to be optically active centers for luminescent thermometer applications using FIR and SBR techniques. It is anticipated that the present work will inspire other researchers to employ multi-mode optical ratiometric thermometry more widely.

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.

Ultrasensitive optical thermometry using Tb3+ doped NaSrGd(MoO4)3 based on single band ratiometric luminescence.

A lot of people are interested in optical thermometry, especially the new single-band ratiometric (SBR) technology for measuring temperature. But since SBR thermometry is still in its infancy, it is highly constrained when compared to the conventional dual-band ratiometric approach. In this paper, we propose a new SBR thermometry technique that is based on both the ground and excited state absorption processes. When these two different processes occur, the green emission of Tb3+ in the low-cost host of NaSrGd(MoO4)3 (NSGM) responds to changes in temperature in a way that is the exact opposite of what you would expect. The maximum luminescence intensity was obtained for an optimum terbium concentration of 40% mol. The resulting chromaticity coordinates (x, y) and high correlated color temperature (CCT) values of the doped phosphors give a thermally stable cold emission in the green region with a color purity of about 92%. Using this intriguing characteristic as a foundation, sensitive SBR thermometry has been successfully developed, and the optical properties of the material have also been thoroughly researched. At room temperature, the relative sensitivity reaches its maximum value of 10.9% K-1. These findings may give important information that may be used in the design of new luminescent thermometers that have excellent performance.

Synthesis and optical spectroscopy of Na3Y(VO4)2:Eu3+ phosphors for thermometry and display applications.

A new Na3Y(VO4)2:Eu3+ (NYVO:Eu3+) phosphor was prepared using the sol-gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to evaluate phase purity and particle size, respectively. The optical properties were investigated by UV-visible absorption, PL, and PLE spectroscopies. The absorption measurements show the formation of the vanadate host by the presence of its characteristic band in the visible region related to VO4 3- groups. The experimental results show that the NYVO:Eu3+ phosphors exhibit high-brightness and thermally stable emission. Under near-ultraviolet (UV) excitation, both the broadband emission from VO4 3- groups and the sharp peak emissions from Eu3+ ions are observed. The highest luminescence intensity was achieved for an optimal europium concentration of 15 mol%. The study of the chromaticity parameters of these compounds gives a thermally stable hot emission in the red domain, with a color purity of about 85%, which qualifies the NYVO:Eu3+ compound as a potential phosphor for light-emitting diode (LED) applications. Thermal sensing using NYVO:Eu3+ phosphors are based on monitoring the luminescence intensity ratio between the NYVO host emission and Eu3+ luminescence lines. Notably, the optical thermometry of NYVO:Eu3+ was characterized based on the fluorescence intensity ratio of VO4 3- and Eu3+ emissions in the 298-440 K range, with maximum absolute and relative sensitivities of 3.4% K-1 and 0.0032 K-1 respectively and a temperature uncertainty of 0.01. NYVO:Eu3+ can then be considered as a potential red phosphor for application in ultraviolet-pumped white light-emitting diodes and as a potential optical thermometer. It provides new possibilities for the design of multifunctional materials for red light-emitting diodes and for non-contact thermometry.

A novel optical thermometry strategy based on emission of Tm3+/Yb3+ codoped Na3GdV2O8 phosphors.

In the last few years, huge progress has been made in the development of remote optical thermometry strategies, due to their non-contact, high-sensitivity and fast measurement characteristics, which are especially important for various industrial and bio-applications. For these purposes, lanthanide-doped particles seem to be the most promising luminescence thermometers. In this study, Tm3+/Yb3+:Na3GdV2O8 (NGVO) phosphors were prepared using a sol-gel method. Under 980 nm excitation, the upconversion (UC) and down-shifting (DS) emission spectra are composed of two visible emission bands arising from the Tm3+ transitions 1G4 → 3H6 (475 nm) and 1G4 → 3F4 (651 nm), a strong emission at 800 nm (3H4 → 3H6) in the first biological window and emission in the third biological window at 1625 nm (3F4 → 3H6), respectively. Accordingly, the luminescence intensity ratio (LIR) between the Tm3+ LIR1 (800/475) and LIR2 (1625/475) transitions demonstrates excellent relative sensing sensitivity values (4.2% K-1-2% K-1) and low-temperature uncertainties (0.4 K-0.5 K) over a wide temperature sensing range of 300 K to 565 K, which are remarkably better than those of many other luminescence thermometers. This phosphor exhibits strong NIR emission at low excitation density, meaning that it has potential uses in deep tissue imaging, optical signal amplification and other fields. The results indicate that Tm3+/Yb3+:NGVO is an ideal candidate for thermometers and particularly for biological applications.

Highly sensitive optical temperature sensing based on pump-power-dependent upconversion luminescence in LiZnPO4:Yb3+-Er3+/Ho3+ phosphors.

In this work, various LiZnPO4:0.5 mol% Ln3+ (Ln = Ho, Er) phosphors with different Yb3+ ion doping concentrations were synthesized by a sol-gel/Pechini method. X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were used to evaluate the phase and morphology of the samples. The UC process was mentioned as the typical emission peaks of Er3+ and Ho3+. For Er3+ and Ho3+, different optical temperature sensing methods are included. The Boltzmann distribution was accompanied by the fluorescence intensity ratio (FIR) for the two green Er3+ emissions originating from thermally-coupled levels. The effect of pump power on sensor sensitivities was extensively studied. The temperature uncertainty is also evaluated. The red and green emissions generated from non-thermally-coupled levels were used for temperature sensing in the Ho3+-activated LiZnPO4. High sensitivities were obtained in the phosphors, and the LiZnPO4:Yb3+/Ho3+ showed the largest absolute sensitivities. LiZnPO4:Yb3+-Er3+/Ho3+ phosphors may be useful in the development of new luminescent materials for optical temperature sensing.