Non-contact Thermometry Research Articles

Unraveling the photophysical response of BaLaLiTeO6:Dy3+ double perovskites with excellent thermal stability for colour tunable LEDs and optical thermometry

The quest for reliable phosphors has accelerated amidst a growing demand for cost-effective, high-performance multifunctional phosphors. Incorporating thermometric application into double perovskite phosphors can enhance their multifaceted features for diverse applications. The present work endeavours to develop a series of BaLaLiTeO6:Dy3+ double perovskites via a solid-state reaction route, stressing their application in next-generation colour-tunable LEDs and non-contact luminescence thermometry. X-ray diffraction, Raman and FTIR spectroscopy analysis were done to make inferences about the structural modifications induced by the substitution of Dy3+ at the La3+ site of BaLaLiTeO6. An extensive investigation of optical characteristics was carried out by diffuse reflectance spectroscopy, photoluminescence spectroscopy and decay curve analysis. Prominent photometric parameters were also evaluated to assess the commercial feasibility of the developed phosphors in photonic applications. Judd-Ofelt parameters were estimated from the photoluminescence excitation spectra of BaLaLiTeO6:Dy3+ for the first time. Furthermore, the values of radiative parameters, fluorescence decay time and quantum efficiency suggested the suitability of the developed phosphor as a competent material. A comprehensive analysis of BaLaLiTeO6:Dy3+ as a thermographic phosphor was done by temperature-dependent photoluminescence spectroscopy. The potential use of this material in luminescence temperature sensing was probed by estimating the thermometric figures of merit based on the fluorescence intensity ratio (FIR). An absolute sensitivity of 22.17 × 10−4 K−1 was achieved at a temperature of 500 K and a remarkable maximum relative sensitivity of 2.34 %K−1 was attained at 250 K, which is much higher than other Dy3+ substituted thermographic phosphors. All these culminated features of BaLaLiTeO6:Dy3+ phosphor proved their prospective applications in thermally stable colour-tunable LEDs, wLEDs and as non-contact optical temperature sensors.

Improved thermometry via luminescence lifetime ratio of Er3+ and Tm3+ operated in the biological window

The luminescent intensity ratio of Lanthanide-doped nanocrystals has been widely used for non-contact thermometry but is still facing difficulties in biological applications due to spectrum distortion caused by tissues. Lifetime-based thermometry is the best alternative to other typical thermometry methods. However, its main drawback is the limited sensitivity. This paper introduces an innovative method known as luminescence lifetime ratio, which enhances luminescence thermometry by combining two emission bands with opposite decay behaviors with temperature. As a proof of concept, a core-shell structure separately containing Tm3+ and Er3+ was synthesized and exhibited two strong emission bands centered at 800 nm and 1530 nm, which are located in the NIR-I and NIR-III biological windows. The commonly used LIR thermometer, an Er/Yb co-doped NaYF4 sample, was also synthesized for comparison. By using chicken tissues of varying thicknesses (1 mm and 3 mm), it was revealed that the deep-tissue penetration and accuracy in biological environments of luminescence lifetime ratio are evidently improved than the widely-used technique of luminescence intensity ratio, although the relative sensitivity of is not much better. In summary, the luminescence lifetime ratio technique enables novel and more accurate temperature sensing within the wavelength range that is suitable for biological applications.

Highly efficient Dy3+ activated Sr9Al6O18 nanophosphors for W-LEDs, optical thermometry and deep learning-based intelligent system for personal identification applications

A novel single-phase Dy3+ activated Sr9Al6O18 nanophosphors (NPs) was synthesized using a solution combustion method with urea as the fuel. When phosphors are excited at 350 nm, their photoluminescence (PL) spectra exhibit strong emissions at 484 and 574 nm, which are associated with the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions. These emissions are attributed to magnetic and electric dipole allowed transitions, correspondingly. It is found that dipole–dipole interactions are the main source of concentration quenching and energy transfer among the activator ions. The prepared NPs show thermal stability up to 480 K having an activation energy (Ea) of 0.2437 eV, as determined by temperature-dependent photoluminescence (TDPL). With a remarkable internal quantum efficiency (IQE) of 66.14 %, the optimized phosphor achieves notable relative sensitivity (Sr) and absolute sensitivity (Sa), estimated to be 2.65 % K−1 and 1.38×10−3 K−1 at 300 K, respectively. Thus, Sr9Al6O18:Dy3+ is a promising material for non-contact optical thermometry applications. Latent fingerprints (LFPs) and latent lip prints (LLPs) can be efficiently produced on a variety of surfaces by using the optimized NPs with the simple powder dusting technique. The prints are made visible under UV light with a 365 nm wavelength. The You Only Look Once version 8 (YOLOv8x) approach analyzes the overall morphological correlations of different minutiae to identify essential minutiae that indicate the identities of people from FPs. Splitting and matching multi-scale fingerprints (FPs) features improves the validity of the authenticating findings. The results show that the recommended method, which improves the entire FP authentication process, offers exceptional accuracy, resilience and speed. The findings provide strong support for the implementation of the optimized NPs in photonic devices, optical thermometers, and advanced forensic applications.

Up/down-conversion luminescence and optical thermometry of Er3+-activated bismuth tellurium borate

Base on up/down-conversion luminescence with thermally coupled energy levels, Er3+-activated phosphors have been significantly promising in non-contact optical thermometry technology. In this study, a new bismuth tellurium borate-based phosphor was synthesized via replacing Bi3+ with Er3+. The structure, morphology, photoluminescence, and concentration quenching are elucidated thoroughly. Particularly, according to the temperature-dependent up/down-conversion luminescence behaviors of Er3+, the fluorescence intensity ratio (FIR, 2H11/2→4I15/2 /4S3/2→4I15/2) of thermally coupled energy levels is investigated. the maximum absolute/relative sensitivities of 0.38 % K−1/0.87 % K−1 (λex = 380 nm), 0.33 % K−1/1.01 % K−1 (λex = 453 nm), and 0.37 % K−1/1.19 % K−1 (λex = 980 nm) is determined. The findings indicate that the resulting phosphor is a promising optical thermometric material.

Highly sensitive dual-mode temperature measurement utilizing completely opposite thermal quenching luminescence

In recent years, phosphors have been used in the field of temperature sensing, which has aroused great interest because of its advantages of quick response, high sensitivity and high accuracy. However, exploring optical thermometers with ultra-high sensitivity remains a challenge. In this work, we have designed and synthesized Sm3+ and Mn4+ co-doped La3Mg2NbO9 phosphor for temperature sensing for the first time by utilizing the anomalous thermal quenching property of Sm3+ ions and the sensitive thermal quenching property of Mn4+ ions. Furthermore, the structure, elemental distribution, morphology and optical characteristics of La3Mg2NbO9:Sm3+,Mn4+ were studied in detail. Benefiting from the different responses of the Sm3+ and Mn4+ ions to temperature, the fluorescence intensity ratios of Sm3+ to Mn4+ in La3Mg2NbO9 samples show excellent optical thermometry performance in the range of 303–463 K. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) values of La3Mg2NbO9:Sm3+,Mn4+ sample reach as high as 0.117 K-1 (@463 K) and 4.48 % K−1 (@303 K), respectively. Furthermore, the maximum of Sa is 0.385 K−1 (@463 K) and the maximum of Sr is 4.54 % K−1 (@303 K) based on the fluorescence lifetime temperature measurement method. The temperature cyclotron curve of the sample proves that the sample has excellent stability and repeatability in temperature measurement. These results demonstrate that the designed La3Mg2NbO9:Sm3+,Mn4+ phosphor is promising for the field of non-contact optical temperature thermometry.

A novel multifunctional Eu3+/Mn4+ co-doping double perovskite phosphor for applications in LEDs and optical thermometry

In recent years, phosphors have played important roles in solid-state lighting, plant growth lighting and optical temperature measurement. In this work, novel La3Mg2NbO9:Eu3+,Mn4+ phosphors were successfully prepared by the high temperature solid phase method and innovative multimode applications were investigated in optical thermometry, plant growth and White-LEDs. The crystal structure, surface morphology, photoluminescence, temperature sensing properties and luminescence mechanism of La3Mg2NbO9:Eu3+,Mn4+ phosphors were investigated in detail. Benefiting from the different responses of Eu3+ and Mn4+ ions to temperature, the La3Mg2NbO9:0.06Eu3+,0.0095Mn4+ sample shows excellent optical thermometry performance in the range of 303 ∼ 478 K. The maximum values of relative sensitivity (Sr) reach 2.7 % K-1 (@478 K) according to the fluorescence intensity ratio method and the maximum of Sr is 5.2 % K−1 (@428 K) based on the fluorescence lifetime method. Furthermore, the electrochromic spectrum of the red pc-LED prepared using La3Mg2NbO9:0.06Eu3+,0.005Mn4+ phosphor perfectly overlapped with the absorption bands of the photosensitive pigments for planting, and another white pc-LED prepared using La3Mg2NbO9:0.06Eu3+,0.0025Mn4+ phosphor emitted bright white light with a color rendering index of 89.8, color coordinate of (0.3468, 0.3557) and correlated color temperature of 4945 K. All the results demonstrate that the La3Mg2NbO9:Eu3+,Mn4+phosphors are promising for the field of non-contact optical temperature thermometry, plant lighting lamps and pc-LED backlit displays.

Luminescent carbon dots encapsulating in Eu3+ doped gahnite spinel nanocomposite for boosting thermal sensing, advanced level III detection and intelligent anti-counterfeiting applications

The exceptional optical properties of carbon dots (CDs) position them as a highly promising category of multifunctional carbon-based nanomaterials. When hydrothermally prepared CDs are incorporated into europium-doped zinc aluminate ZnAl2O4 nanophosphors (ZAO:Eu3+ NPs) synthesized via ultrasonication method, the resulting CDs@ZAO:Eu3+ nanocomposite (NCs) exhibits a broad excitation band, with a prominent peak at approximately 393 nm, perfectly matching the emission wavelength range (500–750 nm) of near-ultraviolet (n-UV) LED chips. Significantly, the CDs (5 wt %)@ZAO:Eu3+ NCs exhibit a remarkable 12.5 folds enhancement in photoluminescence (PL) intensity compared to ZAO:Eu3+ alone, thanks to the Förster Resonance Energy Transfer (FRET) between CDs and Eu3+ ions. This enhancement in luminescence could stem from the CDs capturing electrons and facilitating energy transfer to the luminescent Eu3+ ions. Utilizing CDs to enhance fluorescence presents a straightforward and eco-friendly approach for boosting luminescence properties. Impressively, even under elevated temperatures reaching 420 K, the thermal stability of CDs (5 wt %)@ZAO:Eu3+ NCs remains outstanding, retaining 90 % of its initial luminescence intensity. This highlights its exceptional thermal stability, characterized by a high activation energy of 0.27 eV. With an impressive internal quantum efficiency (IQE) of 87.01 %, the optimized composite also achieves remarkable colour purity (CP), reaching 99.5 %. The relative sensitivity was 1.36 %, at 300 K. Thus, CDs@ZAO:Eu3+ is a promising material for non-contact optical thermometry applications. Utilizing the optimized NCs through a simple powder dusting technique effectively develops latent fingerprints (LFPs) on various surfaces, revealing fingerprints (FPs) under 365 nm UV light. Additionally, the study investigates diverse pore parameters including number, position, size, shape, and inter-spacing. Furthermore, optimized NCs are utilized to create a transparent anti-counterfeiting (AC) ink, offering effective AC features through its red emission under 365 nm UV light.

Probing multifunctional applications of LiCa2Mg2V3O12: Sm3+ phosphor using Judd-Ofelt analysis and dual mode non-contact optical thermometry

LiCa2Mg2V3O12:Sm3+ phosphors have been prepared by solid state method and analysed by X-ray diffraction, EDX-elemental mapping, UV–VIS-NIR spectroscopy, photoluminescence (PL) and temperature dependent photoluminescence (TDPL). The absorption spectra analysis using Judd-Ofelt theory provides the intensity parameters and manifest the covalent nature of Sm-O bond. The PL spectra monitored at 338 nm excitation exhibits emission peaks of Sm3+ at 567, 617 and 651 nm in addition to the broad band emission of LiCa2Mg2V3O12 host. The Commision Internationale deL’Eclairage (CIE) coordinates, correlated color temperature (CCT) and color rendering index (CRI) values elucidate the efficient yellow emission of phosphors. The radiative parameters are evaluated and have outrageous branching ratio and cross section that aids in visible laser applications. The optical thermometry of phosphor is carried out by utilizing FIR method through selecting spectral modes 6H5/2/VO43-, 6H7/2/VO43- and 6H9/2/ VO43-. The mode 6H9/2/ VO43- have higher absolute sensitivity (Sa) and relative sensitivity (Sr) values of 0.4418 K−1 and 1.6079% K−1. The temperature resolution of modes are 0.1633, 0.1677 and 0.1563 K respectively. The thermochromic study reveals the high chromaticity shift (Δs = 0.1869) of phosphor and the Sa(x) and Sr(x) values evaluated based on CIE coordinates are 0.0011 K−1 and 0.2407% K−1 respectively. The PL and TDPL characteristics of prepared phosphor suggest that it have multifunctional application in the fields of lasers, thermo-sensors, thermochromic displays and LEDs.

Ratiometric thermometry using down-conversion luminescence and solid-state lighting application of Er3+ activated strontium tungstate phosphor

Er3+ activated Sr3WO6 double perovskite crystallized in triclinic structure was synthesized via the solid-state reaction method at 1200 °C for non-contact optical thermometry and solid-state lighting. The phosphors under study were characterized via X-ray diffraction, scanning electron microscopy, diffusion reflectance spectra, and photoluminescence techniques. When excited with 380 nm, the Sr3WO6:Er3+ phosphors exhibited intense green emission, corresponds to 2H11/2/4S3/2-4I15/2 transitions of Er3+. The fluorescence intensity ratio of thermally coupled energy levels were computed within 303–513 K and subsequent relative sensitivity (0.56% K−1 at 303 K) was determined. Moreover, the PL intensity maintained 76.28% at LED burning temperature (150 °C) compared to PL intensity observed at room-temperature, denotes good thermal stability. Additionally, the fluorescent behaviour of the phosphors was examined via PL decay lifetime study. The PL quantum efficiency of the phosphor is computed via the Auzel's model using PL decay lifetime, and was obtained to be 80.32% for Sr3WO6:2% Er3+ phosphor.

Temperature sensing materials based on the fluorescence intensity ratio in Li2Ba5W3O15:Dy3+ phosphors

One of the interesting uses of phosphors is the development of non-contact thermometers apart from their usage as visible photonic devices. A series of Dy3+-doped Li2Ba5W3O15 (LBW) phosphors were successfully synthesized using high temperature solid-state reaction process. The crystal structure and morphology of LBW:xDy3+ phosphors were studied using X-ray diffraction (XRD), Rietveld refinements and field effect scanning electron microscopy (FE-SEM) with energy dispersive x-ray (EDX) analysis. The XRD and photoluminescence (PL) analyses validated the effective substitution of Ba2+ ions with Dy3+ ions. Two prominent emission peaks were found at 493 and 583 nm corresponding to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions respectively under 368 nm excitation wavelength. A comprehensive analysis has been carried out on the usage of the Dy3+ doped LBW phosphors in fluorescence intensity ratio (FIR) thermometry. The optical temperature measurement performance of the LBW:xDy3+ phosphor was achieved by utilizing distinct thermal quenching transitions, specifically on 4F9/2→6H15/2,13/2, at temperatures ranging from 293 to 443 K. The as-prepared phosphors demonstrate excellent performance as optical thermometers, with a maximum relative sensitivity (Sr) of 0.7% K−1 at 293 K, an absolute sensitivity (Sa) of 4.68 K−1 at 443 K and a temperature resolution of ∼0.51 at 443 K. These values indicate that the phosphors are highly responsive to changes in temperature, making them suitable for non-contact thermometry applications.

Photo-thermo-optical modulation of Raman scattering from Mie-resonant silicon nanostructures

Abstract Raman scattering is sensitive to local temperature and thus offers a convenient tool for non-contact and non-destructive optical thermometry at the nanoscale. In turn, all-dielectric nanostructures, such as silicon particles, exhibit strongly enhanced photothermal heating due to Mie resonances, which leads to the strong modulation of elastic Rayleigh scattering intensity through subsequent thermo-optical effects. However, the influence of the complex photo-thermo-optical effect on inelastic Raman scattering has yet to be explored for resonant dielectric nanostructures. In this work, we experimentally demonstrate that the strong photo-thermo-optical interaction results in the nonlinear dependence of the Raman scattering signal intensity from a crystalline silicon nanoparticle via the thermal reconfiguration of the resonant response. Our results reveal a crucial role of the Mie resonance spectral sensitivity to temperature, which modifies not only the conversion of the incident light into heat but also Raman scattering efficiency. The developed comprehensive model provides the mechanism for thermal modulation of Raman scattering, shedding light on the photon–phonon interaction physics of resonant material, which is essential for the validation of Raman nanothermometry in resonant silicon structures under a strong laser field.

Clinical value of foot thermometry in patients with acute limb ischemia.

We hypothesized that the severity of foot poikilothermy can be used for better differentiation of grades of acute limb ischemia. Thus, the study aim was evaluation of the value of non-contact foot thermometry, performed using a low-cost infrared medical thermometer, as an adjunct for clinical diagnosis of immediately threatened acute limb ischemia. It was a single-center observational prospective study performed over 3years. Patients with acute limb ischemia of lower limbs grade I-IIB Rutherford treated with urgent revascularization were included. Grade of ischemia was determined independently by two experienced vascular surgeons. Thermometry of the ischemic foot was performed using a medical digital infrared non-contact thermometer (CK-T1501, Cooligg, China) with measuring accuracy of ±0.2°C. Temperature was measured in three points: the dorsal surface of the foot, plantar surface of the foot (both in the metatarsal region), and forehead. The maximal temperature gradient between patient's forehead and foot (∆Tmax F-F) was calculated. Measurements were repeated 6-12h after revascularization. A total of 147 patients were included. Only 3 (2%) patients presented rest pain without sensory loss and motor deficit, while the majority were diagnosed with mild (63/147, 42.8%) or moderate (27/147, 18.3%) motor deficit. The temperature of the ischemic foot varied from 20 to 36.1°C, while median value of the temperature was 26.7 [24.5-29.9] °C on the dorsal surface and 26.8 [24.5-29.6] °C on the plantar surface of the foot (p = 0.85). Patients with Grade IIB ischemia had significantly lower dorsal foot temperature, plantar foot temperature, and larger ∆Tmax F-F than the patients with grades I-IIA: 25.1 [23.9-26.8] °C versus 29.9 [27.6-30.8] °C; 25.2 [23.8-27.5] °C versus 29.6 [28-31.1] °C; and 11.6 [9.7-12.8] °C versus 7.2 [6-9] °C (p < 0.0001). Areas under ROC curve for diagnosis of Grade IIB ischemia were similar for dorsal foot temperature (0.82), plantar temperature (0.81), and ∆Tmax F-F (0.82). The best cutoff value by Youden was ≥9.5°C for ∆Tmax F-F, ≤26.8°C for dorsal, and ≤27.7°C for plantar temperature. Criterion ∆Tmax F-F offered the highest specificity of 86% (95%CI 74.2-93.7) and positive predictive value of 89.2% (95%CI 79.5-93.2), while plantar temperature offered sensitivity of 82.5% (95%CI 70.1-91.3) and negative predictive value of 69.1% (95%CI 57.6-83.2). In multivariate analysis including age, gender, and etiology of arterial occlusion, the criterion ∆Tmax F-F of ≥9.5°C was a unique variable significantly associated with risk of amputation (adjusted OR 2.6, 95%CI 1.2-5.9, p = 0.01). Current study demonstrated that patients with immediately threatening ALI have significantly lower foot temperature than those with viable and marginally threatened limbs. Severe foot poikilothermy at admission is associated with poor outcomes of revascularization, mostly with limb loss.

Laser cooling ytterbium doped silica by 67 K from ambient temperature.

Laser cooling of a 5 cm long, 1 mm diameter ytterbium doped (6.56×1025 ions/m3) silica rod by 67 K from room temperature was achieved. For the pump source, a 100 W level ytterbium fiber amplifier was constructed along with a 1032 nm fiber Bragg grating seed laser. Experiments were done in vacuum and monitored with the non-contact differential luminescence thermometry method. Direct measurements of the absorption spectrum as a function of temperature were made, to avoid any possible ambiguities from site-selectivity and deviations from McCumber theory at low temperature. This allowed direct computation of the cooling efficiency versus temperature at the pump wavelength, permitting an estimated heat lift of 1.42 W/m as the sample cooled from ambient temperature to an absolute temperature of 229 K.

A single phase Li2Ba5W3O15:Dy3+/Eu3+ phosphor for color tunable devices and non-contact optical thermometry

A set of warm white phosphor samples Li2Ba5W3O15 (LBW):xDy3+, yEu3+ were prepared via a high-temperature solid-state process. Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray analysis (EDX) with X-ray diffraction (XRD) are the structural analyses that show the incorporation of Dy3+ and Eu3+ ions into the LBW host matrix, without causing any damage to the lattice structure. Fourier Transform Infrared Spectroscopy (FT-IR) approves the presence of distinct vibrational characteristics of the proposed phosphors. The band gaps of the prepared phosphor samples were determined using diffused reflectance spectral (DRS) data. The energy transfer between Dy3+ and Eu3+ ions was observed, contributing to the adjustable luminescence of the LBW:Dy3+/Eu3+ phosphors. By varying the activator doping levels while keeping the excitation wavelength constant, the emission colors of LBW:Dy3+/Eu3+ phosphors shift from natural white with negligible color purity to a relatively pure orange-red region. The decay curves follow the bi-exponential behavior of decreasing lifetime with increasing concentration of the activator ions. A temperature measurement model using fluorescence intensity ratio (FIR) was developed using D3E0.75 phosphor demonstrating excellent optical temperature measurement properties, with a maximum value of Sr (=0.97 % K−1). Therefore, all the experimental results indicate that the prepared Dy3+/Eu3+ co-doped LBW phosphors can be a suitable choice for UV-excitable warm white lighting devices with color tunability and non-contact optical thermometry measurements.

A highly efficient deep red-emitting Mn4+-powered oxyfluoride nanophosphor developed for plant growth and optical thermometric applications.

This research mainly highlighted an intense deep red-emitting and Mn4+-powered oxyfluoride nanophosphor, Mg14Ge4.99O16F8:0.01Mn4+ (MGOF:Mn), which was synthesized via adopting a scalable synthesis route for commercial temperature sensing and artificial plant growth applications. The electron microscopic analysis confirmed the formation of nanosized particles without any defined shape or size distribution. The obtained nanophosphor exhibited sharp emission peaks at 659 nm and 631 nm under UV (317 nm) and blue excitation (417 nm) owing to Mn4+:2Eg → 4A2g and Mn4+:2T1g → 4A2g transitions, respectively. The emission spectrum is situated in the deep red region of the CIE color diagram where the red color purity approached 100% under both the excitations. The absorption efficiency and the internal and external quantum efficiencies of this red-emitting system were calculated to be 53%, ∼77%, and ∼41%, respectively, under blue excitation of 417 nm, which indicated its potential for indoor plant cultivation. A prototype red LED was fabricated by pasting the red-emitting MGOF:Mn4+ nanophosphor powder on a 410 nm blue LED chip. The resulting electroluminescence spectrum overlapped with those of the important organic pigments of normal plants. Importantly, the thermometric properties of the nanophosphor were evaluated in detail for FIR and lifetime-based thermometry applications. The examined nanophosphor showed an extreme absolute sensitivity of 0.00326 K-1 at 373 K with excellent reproducibility and temperature resolution. Because of the small particle size and high luminescence efficiency, the nanophosphor could be implemented in various nano-devices where non-contact optical thermometry is necessary for high performance.

Er3+-activated Ba2V2O7 upconversion nanosheets for dual-mode temperature sensing.

So far, there has been substantial research on non-contact luminescence thermometry approaches that rely on luminescence intensity ratio (LIR) technology. However, there is limited availability of phosphors doped with Er3+ ions that exhibit on-par luminescence and high sensitivity. In this work, samples of Ba2V2O7:Er3+ were synthesized using a sol-gel method aided by citric acid. The luminescence properties of these samples, including upconversion and down-shifting, were investigated using both ultraviolet and 980 nm laser stimulation. When subjected to ultraviolet (UV) light, the sample exhibits a distinct broadband emission that appears pale green. This emission is a distinguishing property of the sample and is attributed to the presence of V2O72- ions. Upon being stimulated by a 980 nm laser, the sample exhibits standard green up-conversion Er3+ emission bands. Concurrently, an assessment was conducted on the phosphor's ability to measure temperature by analysing the LIR between the thermally coupled 2H11/2, 4S3/2 energy levels (TCELs) and the non-thermally coupled 2H11/2, 4F9/2 energy levels (NTCELs) of the Er3+ ion. The corresponding highest sensitivity of temperature for TCELs and NTCELs can position Ba2V2O7:Er3+ nanosheets as a capable option for materials utilized in temperature-sensing applications.

Novel orange-red-emitting Li2Ba5(WO5)3:Eu3+ phosphor for w-LEDs and non-contact thermometry applications

Novel orange-red-emitting Li2Ba5(WO5)3:Eu3+ phosphor for w-LEDs and non-contact thermometry applications

Three-mode optical thermometry based on multiresponsive Ba1-xSrxLaLiWO6:Er3+, Yb3+ phosphors

Noncontact thermometry based on rare earth-doped phosphors suffer from a single mode of temperature sensing, which leads to lower sensitivity and stability. Herein, a series of Ba1-xSrxLaLiWO6:Er3+/Yb3+ phosphors are prepared with green emission under 980 nm and 380 nm excitation. The luminescence intensities of the samples are effectively enhanced via cation substitution with Sr2+ ions. Such enhancement may be attributed to the more rigid of the crystal structure and the larger band gap in substitution process. The phosphors reveal excellent sensing temperature performances in three modes of upconversion luminescence, downconversion luminescence and fluorescence lifetime, which are systematically investigated within the range of 303 K–573 K depending on the fluorescence intensity ratio and fluorescence lifetime technology. The maximum absolute sensitivity via fluorescence lifetime mode could reach 15.89% μsK-1 and the maximum relative sensitivity via up-conversion luminescence mode could reach 0.98% K-1. All these indicating that Ba1-xSrxLaLiWO6:Er3+/Yb3+ phosphors have enormous utilization prospects for self-calibrating temperature sensors.

An insight into Judd-Ofelt analysis and non-contact optical thermometry of LiCa2Mg2V3O12: Dy3+ phosphors for multifunctional applications

A series of Dy3+ doped LiCa2Mg2V3O12 phosphors have been synthesized by solid state method. The phase composition of the phosphor has been analyzed by X-ray powder diffraction and confirms a cubic phase with Ia-3d space group. The scanning electron microscope images of LiCa2Mg2V3O12:xDy3+ phosphor reveals the surface morphology and is further investigated by its energy dispersive X-ray spectrum. The elemental mapping analysis displays the uniform composition of the elements present in the phosphor. The band gap energy of the phosphors has been determined from the diffuse reflectance spectra. The Judd-Ofelt intensity parameters are determined from the absorption spectra and follows the trend Ω2 > Ω6 > Ω4. The photoluminescence spectra of phosphors excited at 338 nm have intense emission at 494 and 576 nm corresponding to 4F9/2→6H15/2 and 4F9/2→6H13/2 transition and is ascribed to the magnetic and electric dipole allowed transition respectively. The radiative parameters for the optimum dopant concentration x = 0.08 has been calculated. Temperature dependent PL spectra of phosphor displays the diverse thermal response of VO43− group and Dy3+ ion and this can be utilized for the development of thermosensor based on fluorescence intensity ratio (FIR). The phosphor have maximum absloute and relative sensitivity values of 0.0063 K−1 and 0.41% K−1 in the temperature range of 80–400 K. The optical properties of the phosphor suggest that it find applications in the fields of solid-state lighting, temperature sensing, optoelectronic devices and W-LEDs.

Combinatorial ratiometric strategy for continuously highly sensitive thermometry in transparent germanate glass-ceramic containing upconversion nanocrystals

Ratiometric luminescence thermometry is a promising method for non-contact and non-invasive thermometry. Maintaining consistently high temperature sensitivity over a wide temperature range is still a challenge for many ratiometric luminescence thermometers. Here, we have developed a novel transparent germanate glass-ceramic containing NaY3F10:Yb3+/Tm3+/Er3+ nanocrystals. The crystalline content of which remained highly stable during a tunable heat treatment process. Compared with glass, the upconversion luminescence of the glass-ceramic, which originated from the thermally and non-thermally coupled energy levels of Tm3+ and Er3+, was significantly enhanced. Using the temperature-dependent fluorescence intensity ratios of selected upconversion emissions, a ratiometric thermometry scheme with high temperature sensitivity was constructed. The relative sensitivity maintained at a high level (1.30–2.61 %K−1) over the experimental temperature range (323–573 K). The best resolution and repeatability were ±0.13 K and 99.6%, respectively. This transparent glass-ceramic is an excellent candidate for ratiometric thermometry, which is expected to be applied to fibre-optic thermometers.