Relative Sensitivity Sr Research Articles

Design and fabrication of a bimodal emitting phosphor by co-doping two different activators for high sensitivity temperature sensing

Designing of phosphors with multi-emission peaks that show incongruent response to temperature is crucial to design high-efficiency optic fluorescence temperature sensors. Herein, Mn4+ and Dy3+ were co-doped into host lattice Ca2InSbO6 (CIS) with bimodal emissions for fluorescence intensity ratio (FIR) thermometry. The Dy3+-luminescence is insensitive to temperature for its 4f→4f transitions whereas the Mn4+-luminescence is sensitive for its outer 3d→3d transitions. This feature causes almost unchanged intensity of Dy3+-luminescence with increasing temperature and fast decay of Mn4+-luminescence. Utilized the inconsistent temperature dependency of phosphor CIS:Mn4+/Dy3+, highly absolute sensitivity (Sa) of 9.10% K−1 at 573 K and relative sensitivity (Sr) of 2.16% K−1 at 498 K are realized. Additionally, the fluorescence lifetime of Mn4+ is also sensitive to the temperature with Sa of 0.17% K−1 at 348 K and Sr of 1.890 %K−1 at 423 K. This work gives a design idea for researchers in optic temperature sensor field that a phosphor with double activated ions of Dy3+ and Mn4+ is a good choice.

Dual-emitting from Bi[formula omitted], Ln[formula omitted] (Ln [formula omitted] Eu, Sm) co-activated Ca[formula omitted]Sb[formula omitted]O[formula omitted] phosphor for optical temperature measurement

In this paper, a series of Ca(2−x−y) Sb2O7: xBi3+, yLn3+ (Ln = Eu, Sm) fluorescent powder samples were successfully obtained, which used the traditional high-temperature solid-phase synthesis method in the preparation process. Samples of Ca2Sb2O7: Bi3+, Ln3+ (Ln = Eu, Sm) fluorescent powder samples were structurally and optically characterized​ using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), photoluminescence excitation spectroscopy and emission spectroscopy, and fluorescence decay measurements. The results show that the prepared Ca(2−x−y) Sb2O7: xBi3+, yLn3+ (Ln = Eu, Sm) samples have an orthogonal spider web structure, which remains unchanged whether Bi3+ is single doped or Bi3+ is co-doped with Ln3+ (Ln = Eu, Sm). Under ultraviolet lamp (λex=340nm) irradiation, Bi3+ doped Ca2Sb2O7 powder shows a wide emission band centered at 435 nm, which is owing to the 3P1→1S0 transition of Bi3+ ion. Therefore, the effect of Bi3+ and Ln3+ (Ln = Eu, Sm) co-doped Ca2Sb2O7 samples on the luminescence intensity of the samples at different concentrations was studied. When the temperature was varied from 293 K to 483 K, the absolute temperature sensitivity (Sa) of doped Bi3+/Eu3+ and Bi3+/Sm3+ phosphors is 0.001K−1 (at 483 K) and 0.02K−1 (at 293 K), respectively, and the relative temperature sensitivity (Sr) is 1.03% K−1 (at 343 K) and 1.19% K−1 (at 293 K), respectively. These results demonstrate that Ca(2−x−y) Sb2O7: xBi3+, yLn3+(Ln = Eu, Sm) phosphors are prospective double emission thermal thermometers.

Enhanced non-contact optical temperature sensing performance based on upconversion luminescence in Ho3+/Yb3+ codoped ferroelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3

The upconversion luminescence of ferroelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3: xHo3+/0.01Yb3+ is investigated in detail. The prepared samples show intense characteristic emission from Ho3+ ions with a dominant green emission peak located at 547 nm under 980 nm excitation. Among these solid solutions, the 0.94Na0.5Bi0.5TiO3-0.06BaTiO3: 0.0075Ho3+/0.01Yb3+ ceramic possesses the optimum emission. Optical temperature sensing behavior of Ho3+/Yb3+ codoped ferroelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 are investigated through fluorescence intensity ratio (FIR, I656/I547) induced by non-thermally coupled energy levels 5F5→5I8 and 5F4/5S2→5I8 in the range of 303–483 K. A moderate amount of Yb3+ doping in 0.94Na0.5Bi0.5TiO3-0.06BaTiO3: Ho3 + ceramic contributes to the improvement of their optical temperature sensing performance. At T = 303 K, the calculated highest relative sensitivity SR is 0.0042 K-1, which indicates that the optimized 0.94Na0.5Bi0.5TiO3-0.06BaTiO3: 0.0075Ho3+/0.01Yb3+ ceramic is promising as the candidate materials for noncontact optical temperature sensing devices.

Tunable luminescence and efficient energy transfer investigation of a borosilicate phosphor KBSi2O6: Bi3+, Eu3+ with hypersensitive thermal quenching

Energy transfer between Bi3+ and Eu3+ has undergone substantial research but Bi3+ and Eu3+ co-doped luminescent materials with high energy transfer efficiency for temperature sensing are rarely investigated until now. Herein, Eu3+ and Bi3+ co-doped KBSi2O6 phosphors were successfully synthesized by solid-state reaction method. The phase purity structure as well as the element distribution were carefully investigated through X-ray diffraction structural refinement and energy dispersive spectrometer analysis. The characteristic luminescence property and luminescence kinetics of KBSi2O6: Bi3+, Eu3+ were investigated. By the large spectra overlap between the emission spectrum of Bi3+ and excitation spectrum of Eu3+, the energy transfer from Bi3+ to Eu3+ can be inferred. The corresponding decrease of the emission intensity and decay time of Bi3+ in KBSi2O6: Bi3+, Eu3+ provided direct evidence for the effective energy transfer from Bi3+ to Eu3+. The interaction and energy transfer mechanism between Bi3+ and Eu3+ ions were also studied. By increasing the Eu3+ concentration in KBSi2O6: Bi3+, Eu3+, the color-tunable emission from blue to red can be realized. KBSi2O6: Bi3+, Eu3+ shows hypersensitive thermal quenching behavior and the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) are determined to be 1.87 %K−1 and 2.895 %K−1, respectively. All of the above results imply that KBSi2O6: Bi3+, Eu3+ phosphor can be a color-tunable phosphor for optical temperature sensing.

Structural and optical properties of a new structural modification of Na3+3xYb2−x(PO4)3:1% Eu phosphate, where x = 0,1-0,5 and prospective thermometric applications of the compound

The powders of Na3+3xYb2-x(PO4)3: 1% Eu3+ (where x = 0.1, 0.2, 0.3, 0.4 and 0.5) have been synthesized using thermal method in solid state. Their structural and spectroscopic properties were investigated by powder X-ray diffraction, microcalorimetric method (DSC), Raman, infrared, absorption and luminescence studies. It was find that the studied materials belong to the NASICON-type compounds and crystallize in rhombohedral or monoclinic type of structure. Photoluminescence of investigated samples presents typical emission of Eu3+ ions with the dominance of electric dipole transitions and near-infrared bands attributed to Yb3+ ions. Efficient red and infrared emissions under the excitation of 395 nm can be attractive for LED lighting. The highest Yb3+ emission intensity has been registered for the sample with the Na3.9Yb1.7(PO4)3: 1% Eu3+ composition (x=0.3). Ytterbium excited level can be populated by the energy transfer from the Eu3+ ions and can be enhanced by sample heating. Due to the non-radiative processes, the Eu3+ luminescence decay times monitored at 619 nm were bi-exponental. Because of the strong influence of temperature on emission intensities, obtained compounds can be useful for non-contact temperature readout, especially in the high-temperature region (above 600 K). The maximum value of relative sensitivity Sr is equal 2.91%K-1 at 855 K for the sample Na3+3xYb2-x(PO4)3: 1% Eu3+ (x=0.3).

Anthracene-based lanthanide coordination polymer for the sensitive detection of 2-thiazolidinethione-4-carboxylic acid and temperature

An anthracene-based rare earth coordination polymer (CP) [Tb2Cl2(adip)(NMP)3(H2O)] (1) was prepared by solvothermal assembling of Tb3+ and 5,5′-(anthracene-9,10-diyl)diisophthalic acid (H4adip, NMP = N-methylpyrrolidone) and possesses a 3D framework and ligand-based blue emission. 1 could be used as a fluorescent probe to detect 2-thiazolidinethione-4-carboxylic acid (TTCA) and temperature with excellent selectivity, sensitivity and anti-interference ability. Between 0 and 10 μM concentration range of TTCA, the fluorescence quenching constant (Ksv) of 1 reaches 9.78 × 104 M−1 with the limit of detection of 92.6 nM. 1 could also be used as a temperature sensor within 0–60 °C. The maximum relative sensitivity (Sr) was calculated as 5.74% °C−1 at 60 °C and the temperature resolution (δT) is 0.013–0.003 °C corresponding to the above ambient temperature range. The sensitivities of 1 have reached the best level of reported chemical sensors so far. In addition, the mechanisms of fluorescence quenching were studied.

Antithermal Quenching and Multiparametric Temperature Sensing from Mn2+/Tb3+‐Codoped Ca2LaTaO6 Phosphor

Luminescence thermometry plays significant roles in various fields including industrial production, environmental detection, aerospace, and medicine. However, its accuracy improvement remains highly challenging due to the thermal quenching effect of phosphors. Herein, for the first time, a thermal‐activated electron compensation Mn2+‐ and Tb3+‐codoped Ca2LaTaO6 phosphor is developed for multiparametric temperature sensing with tunable emission of Mn2+ and antithermal quenching emission of Tb3+, leading to excellent accuracy at high temperatures. By virtue of the deep electron trap states induced by Mn2+ dopant, the electrons in the deep trap can be thermally activated at high temperatures, which can replenish the attenuated Tb3+ emission caused by thermal quenching, thus bringing out the antithermal quenching phenomenon. On account of the prominent emission properties, the luminescence intensity ratio (LIR) readout and lifetime‐based thermometry are designed, providing a maximum relative sensitivity SR of 3.603% and 1.941% K−1, respectively. Multiparametric temperature sensing and novel data analysis are also employed to further improve the accuracy of the luminescence thermometer. The outstanding relative thermal sensitivity ranging from 8.72% to 16.11% K−1 and temperature uncertainty order of 10−3 are achieved. These results demonstrate that the designed Ca2LaTaO6:Mn2+/Tb3+ phosphor material is a promising thermal‐sensing candidate.

Color-tunable luminescence and temperature sensing in Tm3+/Tb3+/Sm3+ tri-doped eulytite-type structure transparent glass ceramics

Tm2O3–Tb4O7–Sm2O3 tri-doped glass ceramics containing eulytite-type structure were prepared by melt-annealing and crystallization. Controlling crystallization can be achieved by adjusting the heat treatment temperature or time. XRD Rietveld shows that rare earth ions are doped into the Ba3Gd(PO4)3 lattice. A significant reduction in optical band gap values was observed in glass ceramics after heat treatment. Emission spectra and decay curves verified the energy transfer from Tm3+ and Tb3+ to Sm3+, and white light emission was achieved by adjusting the doping concentration of Sm2O3. Based on the temperature-dependent properties of the fluorescence intensity ratios of Sm3+/Tm3+ and Sm3+/Tb3+, the maximum value of the relative sensitivity (Sr) was calculated to be 2.36% K−1. The results show that Tm2O3–Tb4O7–Sm2O3 tri-doped glass ceramic can be a candidate material for w-LEDs and optical temperature measurement.

Photoluminescence and temperature dependent properties of Bi3+, Sm3+ co-doped Ca2YSbO6 phosphor for dual-emitting optical thermometer

Bi3+, Sm3+ co-doped Ca2YSbO6 phosphors with dual-emitting centers were created using a high-temperature synthetic process. Investigations were conducted into the phase structure, luminous characteristics, and optical temperature dependent properties. Under the condition of 320 nm Ultraviolet light excitation, the Ca2YSbO6: Bi3+ phosphor exhibits the 3P1→1S0 emission of Bi3+, which peaked at 402 nm, and the Ca2YSbO6: Sm3+ phosphor exhibits the 4G5/2→6Hn/2 (n = 5, 7, 9 and 11) red emission of Sm3+, which is visible between 550 and 720 nm. Spectrum overlap between the PL spectrum of Bi3+ and the PLE spectrum of Sm3+ served as evidence for the energy transfer (ET) behavior. Furthermore, the conclusion could be supported by the life decay of Bi3+.In the case of optimal UV excitation of 320 nm, the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) values for Ca2YSbO6: Bi3+, Sm3+ were 2.21 × 10−3 K−1 and 0.973% K−1, respectively, at 503 K. The outcomes demonstrated that the Ca2YSbO6: Bi3+, Sm3+ phosphor could perform well as an optical thermometer.

MgGa2O4:Mn2+, Mn4+: A dual-emitting phosphors with unique optical temperature sensing

Single-doped manganese with two luminous centers of MgGa2O4 fluorescent powder was generated through a solid-state reaction. It goes into great detail about the optical characteristics and temperature sensitivity of MgGa2O4:Mn2+, Mn4+. The emission spectrum activated by 322 nm UV light showed a sharp green peak for Mn2+ at 502 nm and a red peak for Mn4+ at 694 nm. Additionally, Mn4+ emission reduces as temperature rises, but Mn2+ emission increases initially before declining, demonstrating that Mn2+ and Mn4+ have differing temperature sensitivity in the MgGa2O4 host. The performance of temperature sensor capability at 80–500 K was investigated by the fluorescence intensity ratio (FIR) technology. The sample’s maximal relative sensitivity (Sr) value is calculated as 1.64% K−1 at 260 K, indicating that MgGa2O4:Mn2+, Mn4+ have considerable potential for optical thermometry.

Triple-Mode upconversion emission for dynamic multicolor luminescent anti-Counterfeiting

Lanthanide (Ln3+) luminescent materials play a crucial role in information security and data storage owing to their excellent and unique optical properties. The advances in dynamic colorful luminescent anti-counterfeiting nanomaterials enable the generation of a high-level information encryption. In this work, a superior thermal, optical wavelength and excitation power triple-mode stimuli-responsive emission color modulation is demonstrated in a lanthanide-doped nanostructured luminescent material. The plentiful emission colors are manipulated by modulating the composition of a fluoride core–shell nanostructure with different Ln3+ at different doping concentrations. The nanomaterials display remarkable excitation wavelength/power-dependent color change, along with temperature-dependent color variation in the range from 298 K to 437 K, with a good relative sensitivity Sr of 1.1387% K−1 at 398 K. The universal optical modulation, combined with the excellent optical and structural stability of the luminescent nanoparticles, renders many advantages for the anti-counterfeiting application. This work explores a universal strategy for the manipulation of triple-mode stimuli-responsive dynamic luminescence and demonstrates its good potential for anti-counterfeiting application.

Tunable emission color and anti-thermal-quenching behaviors in niobates for high-sensitive optical thermometry

Non-contact remote optical thermometers as a significant technique have been extensively developed. However, it is still a challenge to design new Bismuth-doped phosphor materials with tunable spectra for high-sensitive optical temperature sensors. Herein, a novel YxLu1-xNbO4:Bi3+ (0 ≤ x ≤ 1.0) phosphor is constructed by the isomorphic end components LuNbO4 and YNbO4. Owing to the modification of crystal field strength around Bi3+ ions, the emission positions controllably shifted from 475 to 462 nm with the increase of Y3+ ions concentrations. Besides, systematic luminescence modifying from blue to red across the white light region could be achieved via the design of Bi3+→Eu3+ energy transfer (ET). Intriguingly, an anti-thermal-quenching behavior of Eu3+ ion originating from the ET is found in Y0.8Lu0.2NbO4:Bi3+, Eu3+ (YLNO:Bi3+, Eu3+) phosphors, while Bi3+ ion presents a great emission intensity loss with only retaining 46.8% at 383 K. Based on the disparate thermal responses, the fluorescence intensity ratio (FIR) of Eu3+ to Bi3+ demonstrates excellent thermometry properties from 303 to 503 K. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) reach 0.318 K−1 (@328 K) and 1.62%K−1 (@393 K). In addition, the thermochromic performance of the resultant phosphors could be applied to qualitatively estimate the surrounding temperature. The spectral adjustability and high-sensitive of the developed phosphors highlight their multiplicity of applications in non-contact temperature measurement and white LED.

Versatile Ca2LnSbO6:Eu3+/Mn4+ (Ln = La, Y, Gd, and Lu) phosphors for temperature sensing and plant growth LED

AbstractA multifunctional double‐perovskite‐type Ca2LnSbO6 (Ln = La, Y, Gd, and Lu) phosphors with Eu3+ and Mn4+ co‐doped were successfully synthesized and designed to simultaneously apply to temperature sensing and plant growth LED. With temperature varying from 303 to 523 K, the integrated intensity of Mn4+ ions (2Eg → 4A2g) markedly decline swifter comparing to Eu3+ ions (5D0 → 7F2) due to the thermal quenching effect. It implies that Mn4+ is susceptive to the temperature in this work. Eu3+ exhibits high heat resistance, which can be selected as a calibration parameter for the fluorescence intensity ratio temperature sensor. The maximum relative sensitivity (Sr) values of Ca2LnSbO6:1%Eu3+, 0.5%Mn4+ (Ln = La, Y, and Gd) phosphor are estimated as 2.19% K−1 at 443 K, 1.68% K−1 at 503 K, and 1.80% K−1 at 483 K, respectively. They are superior to many recent emerging phosphors. Moreover, upon 365 nm excitation, Ca2LnSbO6:1%Eu, 0.5%Mn (Ln = La, Y, Gd, and Lu) phosphors display a wide red emission peaking at 696, 680, 677, and 684 nm, respectively. They come from the overlapped of 2Eg–4A2g of Mn4+ and 5D0–7F4 transition of Eu3+. Their full widths at half maximum are 34, 35, 35, and 29 nm, respectively. They are all perfectly overlapping the absorption curves of chlorophyll a and chlorophyll b, and their fabricated red phosphor‐converted light‐emitting diode device ulteriorly corroborated the promising applications for plant growth. Markedly, the systematic analysis of their crystal chemistry and site preferentially occupancy is first reported and discussed by the bond valence theory.

Excellent Sensitive Temperature Sensing Performance Based on Fluorescence Intensity Ratio Technique of Yb3+/Er3+ Codoped Gd2(WO4)3

The efficient upconversion (UC) particles based on fluorescence intensity ratio (FIR) technique are developed for application in novel temperature sensors. Herein, Yb3+/Er3+‐codoped Gd2(WO4)3 particles are prepared by coprecipitation method and subsequent calcination. The phase structure and surface morphology of the particles are systematically analyzed. The UC emission spectrum of Gd2(WO4)3:Yb3+/Er3+ particles are mainly composed of two strong emission bands centered at 530 and 551 nm, respectively. Moreover, the optimum doping concentration of Yb3+ and Er3+ is fixed at 10% and 2%, respectively. UC emission mechanism based on two‐photon process is investigated by studying the pump power excitation dependence and fluorescence decay behavior of Gd2(WO4)3:10%Yb3+/2%Er3+ particles. The excellent temperature sensing capability of Gd2(WO4)3:10%Yb3+/2%Er3+ particles is implemented from thermally coupled levels (TCLs) of Er3+. Notably, the maximum absolute sensitivity (S a) and relative sensitivity (S r) based on TCLs by 2H11/2/4S3/2 levels are 1.39 %K−1 (at 518 K) and 1.18 %K−1 (at 293 K), respectively. As a result, Gd2(WO4)3:10%Yb3+/2%Er3+ particles have a great potential for application in noncontact temperature sensors.

A NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods with infrared thermally enhanced upconversion luminescence for optical thermometers

A novel strategy for optical thermometers is reported based on the NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods which generate thermally enhanced near-infrared upconversion emission. The fluorescence intensity ratio (FIR) between the near-infrared emission of Tm3+ (3H4→3H6) and the green emission of Er3+ (4S3/2 → 4I15/2) as a function of temperature are studied. The relative sensitivity (Sr) of FIR (3H4→3H6/4S3/2 → 4I15/2) is compared with that of classical FIR (2H11/2 → 4I15/2/4S3/2 → 4I15/2). The results show that FIR (2H11/2 → 4I15/2/4S3/2 → 4I15/2) is suitable for low temperature, while FIR (3H4→3H6/4S3/2 → 4I15/2) is suitable for high temperature. Using FIR with higher Sr at different temperature intervals can keep the Sr of the thermometer at a higher value (0.67–1.07 %K−1) in the temperature range of 293–523 K. The results show that NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods can be used as high-quality candidates for thermometers with high sensitivity and wide temperature range.

Enhanced piezoelectricity and non-contact optical temperature sensing performance in Er3+ ion modified (K,Na)NbO3-based multifunctional ceramics

Rare earth ions doped ferroelectrics have attracted wide attentions due to their multifunction characteristics with both ferroelectric/piezoelectric properties and intriguing photoluminescence performance, which show great prospects for future multifunctional devices. In this work, a novel rare earth Er3+ ion modified potassium-sodium niobate (KNN) based ceramics were elaborately designed and prepared by the conventional solid-state reaction. The microstructure, phase structure, electric properties and photoluminescence performance of the Er3+ ion modified KNN-based ceramics were systematically investigated. Enhanced piezoelectricity (a considerable d33 of exceeding 300 pC/N and a large d33* up to 500 p.m./V) was realized through optimizing the substitution of BaZrO3 by (Er0.5,Na0.5)ZrO3. Both down-conversion and up-conversion photoluminescence emissions were detected in the optimal composition. The temperature-dependent upconversion emissions of the optimal Er3+ modified ceramic sample in the temperature range of 303–573K were verified to be applicable for non-contact optical temperature sensing with a maximum sensitivity Sa of 0.0028 K-1 and a peak relative sensitivity Sr of 0.96% K−1. Moreover, low-temperature sensing performance with a maximum Sr of 16.7% K−1 in the temperature range of 80–280K was also presented based on the temperature-dependent down-conversion emissions. With both decent electrical properties and intriguing photoluminescence performance, the Er3+-modified KNN-based ferroelectrics exhibit good application potential in the future multifunctional optoelectronic devices.

Eu3+ Single-Doped Phosphor with Antithermal Quenching Behavior and Multicolor-Tunable Properties for Luminescence Thermometry

To date, non-contact luminescence thermometry methods based on fluorescence intensity ratio (FIR) technology have been studied extensively. However, designing phosphors with high relative sensitivity (Sr) has become a research hotspot. In this work, Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors with a high Sr value for dual-emitting-center luminescence thermometry are developed and proposed. The anti-thermal quenching behavior of Eu3+ originating from the energy transfer (ET) of host → Eu3+ is found and proved in the designed phosphors. Interestingly, adjustable color emission from blue to orange can be achieved. Surprisingly, the degree of the anti-thermal quenching behavior of Eu3+ gradually reduces from 240 to 127% as the Eu3+ doping content increases from 0.005 to 0.05 mol, attributed to most Eu3+ being located in the low symmetrical [Ca1O8] dodecahedral site. According to the differentiable responses of the host and Eu3+ to temperature, the maximal Sr value reaches 3.369% K-1 (383 K). Moreover, the ambient temperature can be intuitively predicted by observing the emitting color. Owing to the excellent performance in optical thermometry, color-tunable properties, and outstanding acid and alkali resistance for polydimethylsiloxane (PDMS) films, the developed Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors are expected to be prospective candidates in luminescence thermometers and LED devices in various conditions.

High-sensitivity NaYF4:Yb3+/Ho3+/Tm3+ phosphors for optical temperature sensing based on thermally coupled and non-thermally coupled energy levels.

Non-contact optical temperature sensors are highly sought after by researchers due to their satisfactory temperature resolution (δ(T) < 0.1 °C), high relative thermal sensitivity (Sr > 1% °C-1), fast temporal response (t < 0.1 s), and long-term optical stability. In this study, NaYF4:Yb3+/Ho3+/Tm3+ upconversion nanoparticles were prepared by a solvothermal method, and their crystal structure, microscopic morphology, and luminescence mechanism, together with the temperature sensing properties of the specimens, were investigated. Under 980 nm laser excitation, the specimens exhibited strong upconversion luminescence, and the emission peaks corresponded to the characteristic energy level jumps of Ho3+ and Tm3+, respectively. The temperature-dependent luminescence spectra of the samples were investigated based on the fluorescence intensity ratio (FIR) technique over a temperature gradient of 295-495 K. The samples are based on thermally coupled energy levels (TCLs: 1G4(1,2) → 3H6(Tm3+)) and non-thermally coupled energy levels (NTCLs: 3F3 → 3H6(Tm3+) and 5F3 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 1G4 → 3H6(Tm3+), 3F3 → 3H6(Tm3+) and 5F5 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 5F4 → 5I8(Ho3+)) for temperature sensing performance. The maximum absolute sensitivity (Sa), relative sensitivity (Sr), and minimum temperature resolution δ(T) were found to be 0.0126 K-1 (495 K), 1.7966% K-1 (345 K), and 0.0167 K, respectively, which are better than those of most sensing materials, and the simultaneous action of multiple coupling energy levels can further improve the temperature precision. This study indicates that the sample has a good value for optical temperature measurement and also provides new ideas for the exploration of other high-quality optical temperature sensing materials.

UVB upconversion of LiYO2:Ho3+,Gd3+ for application in luminescence thermometry.

Development of novel ultraviolet (UV) upconversion materials has been emerging as a hot research topic for application in tunable UV lasers, photocatalysis, sterilization, tagging, and most recently luminescence thermometry. We readily synthesized a series of Ho3+/Gd3+ co-doped LiYO2 upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO2:Ho3+,Gd3+ polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from Gd3+ 6Pj (j = 7/2, 5/2, 3/2) excited states. By means of steady and dynamic photoluminescence spectra, we systematically investigated the involved two-photon absorption upconversion as well as the accompanying energy transfer processes between Ho3+ and Gd3+ ions in the LiYO2 host lattice. Interestingly, the distinguishable UVB luminescence constituents from Gd3+ 6Pj excited states exhibit sensitive temperature dependence in a 353-673 K range. Shedding light on thermal equilibria between Gd3+ 6Pj UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of 6P7/2-6P3/2 thermally coupled levels, it works over a temperature range of 373-673 K with a maximum relative sensitivity (Sr) of about 1.07% K-1 at 373 K, and its 6P7/2-6P5/2 counterpart works over 353-533 K with a maximum Sr of about 0.83% K-1 at 353 K. Overall, our study provides a new pathway to develop UV upconversion materials, and promotes the application of Gd3+-related UV luminescence constituents in sensitive temperature sensing over a wide temperature range.

Multiple ways for temperature detection based on La2MgTiO6 double perovskite co-doped with Mn4+ and Cr3+ ions

Optical thermometers play an increasingly important role in enabling allowing work in harsh conditions in low temperatures. In this work, multiple ways of the non-contact temperature readout based on La2MgTiO6 double perovskite doped and co-doped with transition metal ions (Mn4+ and Cr3+) have been investigated for the first time. It was possible thanks to the occurrence of the host emission – [TiO6] groups, as well as the spin-forbidden emission 2E–4A2 of the Mn4+ and Cr3+ ions. The potential of the temperature sensing performance of La2MgTiO6: Mn4+, La2MgTiO6: Cr3+, and La2MgTiO6: Mn4+, Cr3+ luminescent thermometers was examined. It was found that the optimal concentration of manganese ions is 0.8 %. In addition, the La2MgTiO6:Mn4+, Cr3+ has the potential for a multimodal approach to temperature detection. It was shown that the relative sensitivity (Sr) can be easily modified by the sample composition and dopant concentration. The outstanding relative sensitivities of 2.68 % K−1 and 1.74 % K−1 at 220 K from La2MgTiO6: 0.1 % Cr3+ and La2MgTiO6:0.8 % Mn4+, 0.5 % Cr3+, respectively, were obtained.