Relative Sensitivity Sr Research Articles

Broad-scope dual-mode modulation thermometry based on up-conversion phosphor GaNbO4: Yb3+/Er3+

Fluorescence temperature measurement technology has set off another upsurge in non-contact temperature measurement, but still suffers from the large error for single-mode thermometry. Herein, in a broad temperature range of 93–633 K, a dual-mode modulation thermometry based on up-conversion phosphor of GaNbO4:Yb3+/Er3+ is realized with the maximum relative sensitivity (Sr) of 11.7% K−1 (93 K) and 13.1% K−1 (123 K), respectively. GaNbO4:Yb3+/Er3+ phosphors were synthesized by high temperature solid-state method. The structure, surface morphology and the optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The fluorescence intensity ratio (FIR) readout method based on Er3+ thermal-coupled energy level (TCL) and non-thermal-coupled energy level (NTCL) was used to achieve the dual-mode temperature measurement with high temperature resolution and good repeatability in GaNbO4:5 mol% Yb3+ and 5 mol% Er3+ phosphors. All the results show that GaNbO4:Yb3+/Er3+ phosphors have great application potential in high sensitivity broadband thermometry.

High sensitivity and multicolor tunable optical thermometry in Bi3+/Eu3+ co-doped Ca2Sb2O7 phosphors

Currently, with increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, a novel phosphor with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity is more and more urgent to develop. In this work, an efficient dual-emitting center optical thermometry with high sensitivity and multicolor tunable in Ca2Sb2O7:Bi3+, Eu3+ phosphor is firstly designed and successfully prepared. Under 330 nm excitation, the fabricated phosphor presents the featured and distinguishable emissions of Bi3+ and Eu3+ ions. The high efficiency energy transfer from Bi3+ to Eu3+ ions is proved and its corresponding mechanism belongs to dipole-dipole interaction. By modulating the ratio of Bi3+/Eu3+, the multicolor changes from blue to pink are realized. Based on the discriminative thermal quenching behavior between Bi3+ and Eu3+, the fluorescence intensity ratio of Eu3+ to Bi3+ in Ca2Sb2O7 samples illustrates excellent optical thermometry performance from 298 to 523 K. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) reach as high as 0.2773 K−1 at 523 K and 2.37% K−1 at 448 K, respectively. Notably, the discriminated surrounding temperature can be directly confirmed by observing the emitting color from purple to orange-red with the temperature increase from 298 to 523 K. Furthermore, the as-prepared phosphor materials also demonstrate outstanding repeatability and excellent reversibility. These results exhibit that the designed Ca2Sb2O7:Bi3+, Eu3+ phosphors have great promising applications in the field of non-contact optical temperature thermometry and thermochromic.

The synthesis of Er3+/Yb3+/K+ triple-doped NaYF4 phosphors and its high sensitivity optical thermometers at low power

Optical Thermometry is popular among researchers because of its non-contact, high sensitivity, and fast measurement properties. In the present experiment, Er3+/Yb3+/K+ co-doped NaYF4 nanoparticles with different K+ concentrations were synthesized by solvothermal method, and the samples showed bright upconversion green emission under the excitation of a 980 nm laser. The powder X-ray diffractometer and transmission electron microscope were used to characterize the crystal structure and its surface morphology, respectively. The spectral characteristics of nanoparticles with K+ doping concentration from 10% to 30% (Molar ratio) were investigated by fluorescence spectroscopy, and it was observed that the fluorescence intensity reached the maximum at the K+ concentration of 20%, after which the intensity weakened when the K+ content continued to increase. According to the dependence between the luminescence intensity of the sample and the laser power density and fluorescence lifetime, the intrinsic mechanism was carefully investigated. Temperature-dependent spectra of the samples were recorded in the temperature range of 315–495 K， and the maximum values of absolute sensitivity (Sa) and relative sensitivity (Sr) were measured at 0.0041 K−1 (455 K) and 0.9220%K−1 (315 K). The experimental results show that K+/Er3+/Yb3+ triple-doped NaYF4 green fluorescent nanoparticles (GFNs) have good prospects for applications in display devices, temperature sensing, and other fields.

Fluorescence modulation in Pr3+-doped MGd2O4 (M = Sr, Ba) by the site engineering strategy

The crystal-field splitting of the 4f5d and 4f electronic configurations of lanthanide luminescent ions can be modulated by their local coordination environments. In this work, the fluorescence properties of Pr3+:MGd2O4 (M = Sr, Ba) phosphors are successfully modulated based on the site engineering in the M2+ sites. The obtained results indicate that Pr3+ ions would occupy both Sr2+ and Gd3+ sites in Pr3+:SrGd2O4, while only entering into Gd3+ ones in Pr3+:BaGd2O4. Such an obvious local coordination difference of Pr3+ ions between Pr3+:SrGd2O4 and Pr3+:BaGd2O4 results in an obvious distinction of relevant fluorescence performance. The quenching mechanism of Pr3+ ions in SrGd2O4 conforms to a quadrupole-quadrupole interaction at the lower Pr3+-doped contents and becomes a dipole-dipole interaction with higher Pr3+-doped dosages. In contrast, the quenching mechanism of Pr3+ ions in Pr3+:BaGd2O4 is mainly caused by dipole-dipole interaction. Moreover, combined with the temperature-dependent fluorescence distinctions between the two kinds of Pr3+-doped sites, Pr3+:SrGd2O4 shows an outstanding temperature sensing with a maximum relative sensitivity Sr of 2%·K−1 at 150 K. What is discussed in this study demonstrates the potential application of site engineering strategy in adjusting the fluorescence properties of Pr3+ ions and also provides a feasible path for the development of Pr3+-based materials.

Photon upconversion-based non-invasive temperature sensing using Gd1−x-yYbxEr yScO3 perovskite nanocrystals

High thermal stability, high bandgap, and low phonon energy (452 cm−1) of GdScO3 perovskite make it ideal for optical applications, particularly for infrared (IR)-to-visible photon upconversion (UC) emission. This phase has been typically synthesized either in single crystal or in thin film forms which require high temperatures and a longer time. Thin films/single crystals of GdScO3 have limited optical application mostly as lasing material. Unexpectedly, the photon UC-based emission and correlated applications are completely ignored in this host so far. Herein, we have successfully synthesized pristine and Yb3+, Er3+ co-doped GdScO3 nanocrystals (powder) at low temperatures and further analyzed their crystal structure, phase, and optical absorption and emission properties at length. The photon-UC property in GdScO3 nanocrystal has been studied for the first time. Further, the material has been used for the non-contact luminescence-based temperature sensor application also. Our study shows that the maximum relative sensitivity (Sr) and absolute sensitivity (Sa) obtained for Yb3+, Er3+: GdScO3 nanocrystal is better than most of the reported oxide-based perovskite materials.

Ultra-sensitive luminescence ratiometric thermometry from 2E→4A2 transitions of AlTaO4:Cr3.

In recent years, non-contact ratiometric luminescence thermometry has continued to gain popularity among researchers, owing to its compelling features, such as high accuracy, fast response, and convenience. The development of novel optical thermometry with ultrahigh relative sensitivity (Sr) and temperature resolution has become a frontier topic. In this work, we present a novel, to the best of our knowldege, luminescence intensity ratio (LIR) thermometry method that relies on AlTaO4:Cr3+ materials, based on the fact that they possess both anti-Stokes phonon sideband emission and R-line emission at the 2E→4A2 transitions and have been confirmed to follow the Boltzmann distribution. In the temperature range 40-250 K, the emission band of the anti-Stokes phonon sideband shows an upward trend, while the bands of the R-lines show the opposite downward trend. Relying on this fascinating feature, the newly proposed LIR thermometry achieves a maximum relative sensitivity of 8.45%K-1 and a temperature resolution of 0.038 K. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr3+-based LIR thermometers and provide some novel entry points for designing excellent and reliable optical thermometers.

Impact of temperature on optical spectra and up-conversion phenomena in (Lu0.3Gd0.7)2SiO5 crystals single doped with Er3+ and co-doped with Er3+ and Yb3+

Optical absorption and luminescence spectra were recorded at different temperatures for the Czochralski grown crystals of Lu2SiO5-Gd2SiO5 solid solution (LGSO) single doped with Er3+ and double-doped with Er3+ and Yb3+. Optical anisotropy and intensities of Er3+ transitions in LGSO were determined from analysis of room temperature polarized absorption spectra. The crystal field splitting of multiplets and linewidths of Er3+ transitions were derived from low-temperature 6 K absorption and luminescence spectra. Spectra of the Er3+ luminescence excited at 380 nm and of up-converted luminescence excited at 803 nm and 975 nm were recorded for samples with different Yb3+ concentration as a function of temperature between 300 K and 775 K. Thermographic parameters of LGSO:0.5%Er,5%Yb sample derived for FIR (2H11/2/4S3/2) are comparable to those observed in other hosts co-doped with Er and Yb ions, corroborating suitability of this system for the purpose of optical thermometry. For all samples studied the relative thermographic sensitivity Sr(max) values for the 4S3/2/4F9/2, 4F7/2/4S3/2 and 4F7/2/4F9/2 pairs are smaller as compared to 2H11/2/4S3/2 pair but they occur at higher temperatures and therefore may be of interest for specific applications.

Eu3+-doped La2(MoO4)3 phosphor for achieving accurate temperature measurement and non-contact optical thermometers

In this study, La2(MoO4)3 doped with Eu3+ was synthesized by the high-temperature solid-state method. The phase composition of the Eu3+-doped La2(MoO4)3 sample was confirmed by X-ray powder diffraction (XRD) analysis, and the microstructure was observed via the scanning electron microscopy (SEM). Under the excitation at 211 nm, the room temperature emission spectra of Eu3+ in the samples with different doping levels were recorded. In addition, the prepared La2(MoO4)3:xEu3+ (x = 0–0.25) phosphors were color tunable. A non-contact optical thermometer with high sensitivity and high-temperature resolution was fabricated based on the different thermal quenching behaviors of the Mo–O group and Eu3+ center. The fluorescence intensity ratio (FIR), temperature resolution (ΔT), maximum absolute and relative sensor sensitivity (Sa and Sr) of La2(MoO4)3:Eu3+ were calculated according to different thermal quenching effects between room temperature (298K) and 573K of Eu3+ and Mo–O group. These results show that La2(MoO4)3:Eu3+ has excellent sensitivity and temperature resolution, good reversibility and reliability, as Sa = 0.0525 K-1, Sr = 0.3724.% K−1, ΔT = 0.0806 K and the FIR error was only 0.62%. Therefore, the Eu3+-doped La2(MoO4)3 is a promising candidate material for high performance non-contact optical thermometers.

Size influence on optical thermometry of Er3+/Yb3+ Co-doped Y2O3 microspheres: From TCLs and Non-TCLs

Realization and optimization of enhanced/tunable optical luminescence properties is highly demanded for reliable and accurate temperature sensing. In this work, uniform monodisperse spherical Er3+/Yb3+ co-doped Y2O3 microcrystals of four different sizes have been synthesized via homogeneous precipitation by changing the reaction time, and the tuning of luminescence intensity/color was achieved by the controllable particles size. On this basis, by studying the particle size dependence of temperature sensing performance, we found that the behavior of absolute sensitivity (Sa) and relative sensitivity (Sr) have highly size dependence. Interestingly, when different FIR strategies were used (thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs)), the sensitivity exhibits the opposite behavior. Importantly, when using the non-TCLs strategy, the maximum Sa value for the smallest phosphors was 1.084 K-1, leading to ∼246 times improvement compared to TCLs-based Sa. The ultrahigh Sa indicated that the Er3+/Yb3+ co-doped Y2O3 phosphors have potential in temperature detection, and the results are of guiding significance to studying the sensitivity of Y2O3 particle size-dependent temperature measurement.

Structural-suppressing concentration quenching in dysprosium single-phase white emission and their application in optical thermometric and white light-emitting devices

Single Dy3+ doped material is indispensable to establish single-phase white emission. However, concentration quenching (CQ) and poor stability limit its wider application. Herein, Dy3+-doped Ca3LuAl3B4O15 (CLAB:Dy3+) is reported to be an advanced dual-emitting micro phosphor with promising optical properties making it a promising applicant with potential applications in thermometric and n-WLEDs. The host has a highly disordered crystal structure, suppressing the CQ phenomena of Dy3+, and attains a high doping level. Using the Kubelka–Munk equation, the optical bandgap Calculated for the matrix is 4.66 eV, which is ideal for n-WLEDs. Under 350 nm UV light, the prepared CLAB:Dy3+ displayed emissions at 476 nm and 569 nm with a CIE diagram of (0.382, 0.402) and IQE up to 18.3%. The Blass and Dexter model analyzed the energy migration (EM) mechanism. The dual emissions in CLAB:Dy3+ have distinct thermal reactions caused by thermal quenching. The temperature sensing properties of CLAB:0.08Dy3+ ranging from 300 to 500 K was examined and showed a superb Boltzmann distribution behavior between 455 nm and 476 nm fluorescence intensity ratio (FIR) and the optimum relative sensitivity SR value of 1.46% K−1. Employing the CLAB:Dy3+, a fabricated phosphor-converted white light-emitting diode (pc-WLED) emitted white light with CIE (0.36, 0.39), a color rendering index (CRI = 67.5), and a low color coordinate temperature (CCT = 4624 K). These findings suggest that this incredibly efficient single-phase white-emitting material has great potential for optical thermometric and pc-WLEDs.

Strong electron–phonon coupling of Cr3+ ion provides an opportunity for superior sensitivity cryogenic sensing

Nowadays, optical temperature measurement is becoming a reliable and advanced technology. Most of optical temperature sensing materials have been reported in the first biological temperature region or even higher. However, cryogenic optical sensing materials seem to be ignored. Here, Cr3+-doped SrGa12O19 is reported, exhibiting a obvious sharp peak at 696 nm (2E→4A2) and near-infrared emission at 750 nm (4T2→4A2) at 77 K. As the temperature increases, the transition of 2E→4A2 is suppressed and the emission of 4T2 is broadened due to the increasing electron–phonon coupling effect. This feature provides an opportunity to obtain the obvious discrepancy of fluorescence intensity, and further realize the superior cryogenic sensing performance based fluorescence intensity ratio (FIR) method with the maximum absolute sensitivity (Sa) of 0.0085 K−1 and relative sensitivity (Sr) of 2.62 %·K−1 at 77 K. The value of Sr is 138.6 % higher than that of CaHfO3:Cr3+ system and the temperature uncertainty (δT) is one order of magnitude lower than the most popular ruby Al2O3:Cr3+, showing superior cryogenic sensing ability. This work not only exhibits a novel cryogenic sensing material but also provides a train of thought for designing cryogenic thermometer.

Supersensitive nanothermometer based on CdSe/CdSxSe1-x magic-sized quantum dots with in vivo low toxicity

We report on the temperature dependence of the photoluminescence spectrum of CdSe/CdSxSe1-x magic-sized quantum dots (MSQDs), as well as the CdSe/CdSxSe1-x MSQDs biocompatibility in Drosophila melanogaster. We found that the emission intensity of CdSe/CdSxSe1-x MSQDs decreases while the full width at half-maximum (FWHM) increases with the temperature in the range of 306–343 K, under excitation at 376 nm. Combining these two characteristics, an optical nanothermometer was developed with a maximum relative thermal sensitivity (Sr) of 6.9 %K−1 at 306 K, based on the ratio between the FWHMand the maximum emission intensity, which is one of the highest values of Sr reported in the literature related to ratiometric optical thermometry systems. Additionally, our results suggest that lower concentrations of CdSe/CdSxSe1-x MSQDs are biocompatible in model of Drosophila melanogaster. Taken together, our data suggested a translational potential for fluorescence and thermal images in nanomedicine with low toxicity.

Enhanced luminescence properties and device applications of Tb3+-doped Cs4PbBr6 perovskite quantum dot glass

Cs4PbBr6 perovskite quantum dots (QDs) have unique optoelectronic properties and are expected to become a new generation of luminescent materials. However, poor stability, low photoluminescence quantum yield (PLQY), and poor understanding as to the origin of photoluminescence behavior limit its further application. In this study, a series of Tb3+-doped Cs4PbBr6 perovskite QD glasses with excellent stability were obtained through the optimization of Tb3+ doping concentration and in-situ crystallization temperature. Density functional theory calculations and experimental characterization showed that an appropriate amount of lattice-incorporated Tb3+ ions can reduce structural defects in QDs, improve the PLQY, and reduce the QD heavy-metal requirements. Notably, the maximum PLQY value reached 47%, which is near to the Cs4PbBr6 perovskite crystal. Furthermore, a high-performance white light-emitting diode (WLED) device was prepared. The device featured a color rendering index of 80 and luminous efficiency of 41 lm W−1. Finally, a QD glass with double emission peaks was prepared by controlling the in-situ crystallization temperature (550 °C). The temperature sensitivity of the QD glass was then studied using the fluorescence intensity ratio method. The maximum relative temperature sensitivity (Sr) reached 2.03% K−1, which is higher than the previously reported value. Thus, the method proposed in this study can greatly improve the photoluminescence properties of Cs4PbBr6 QD glass and expand its applications in WLED and visual temperature sensing.

An optical thermometry based on near-infrared luminescence of LiGaSiO4:Cr3+ phosphors excited by red light

A near-infrared luminescent material LiGaSiO4:Cr3+ with triple temperature detection function was synthesized in this paper. The results show that the sample has the best Near-infrared luminescence (NIR) performance under the excitation of 620 nm red light when the concentration of Cr3+ is 0.05%. The emission peak in the near infrared region (705 and 721 nm) is due to the 2E→4A2 energy level transition of Cr3+, and the emission peak in the red region (670 nm) is due to the 4T2→4A2 energy level transition of Cr3+. The obtained results show that the dependences of temperature on three fluorescence intensity ratio (FIR) models including 670/705, 705/721 and 721/605 all show excellent linearity, indicating that high temperature sensing sensitivity and accuracy can be obtained via the combination of three FIR models. Furthermore, FIR (705/721) can provide the highest temperature sensing performance and its relative sensitivity (Sr) is up to 4.32 K-1. All these results indicate LiGaSiO4: Cr3+ possessed great potential in the application of temperature sensing.

Systematical site investigation and temperature sensing in Pr3+-doped M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu)

Site engineering is an important modulation strategy for adjusting the physicochemical properties of lanthanide luminescent ions and shows growing applications in the optoelectronic field. Herein, we explored the influence of changing M2+ (or RE3+) ions on the occupation preference of Pr3+ ions and related crystal-field splittings in Pr3+:M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu). The obtained results indicated that Pr3+ ions possess two kinds of doping sites (M2+ (Site Ⅰ) and RE3+ (Site Ⅱ)) in Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9, while only occupying Site Ⅰ in Pr3+:Sr3Sc4O9 and Pr3+:Ba3Sc4O9. The variation of RE3+ ions has little impact on the crystal-field splitting of both the two types of Pr3+ luminescent sites, and by contrast, replacing M2+ ones influences the energy-level splitting of the 3H4 multiplet of Site Ⅰ obviously. Moreover, we found that the host emission of M3RE4O9 stemming from intrinsic oxygen defects shows an apparent thermally induced fluorescence quenching phenomenon. And based on the defect and Site Ⅱ emissions, both Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9 exhibit excellent temperature sensing performance, yielding maximum relative sensitivity (Sr) of 8.40%·K−1 (132K) and 7.89%·K−1 (129K), respectively. This work enriches the site engineering strategy in Pr3+-based optical functional materials and broadens the relevant application in temperature sensing.

Investigation on the determinant of upconversion luminescence efficiency and temperature measurement sensitivity based on AWO4 (Ba, Sr, Ca, and Mg): Er3+/Yb3+ microcrystals

In this work, a comparative study of the upconversion (UC) luminescence properties of E r 3 + − Y b 3 + -co-doped A W O 4 ( A = B a , Sr, and Ca) scheelite phosphors and E r 3 + − Y b 3 + -co-doped M g W O 4 wolframite phosphors is reported. Under 980 nm excitation, all the samples emit green and red emissions. The E r 3 + − Y b 3 + -doped M g W O 4 phosphor has a higher UC emission intensity. Furthermore, the optical temperature sensing properties in E r 3 + − Y b 3 + -co-doped A W O 4 ( A = B a , Sr, Ca, and Mg) phosphor samples are investigated. The relative sensitivity ( S r ) based on thermally coupled levels (TCLs) increases gradually with an increase in matrix phonon energy. The absolute sensitivity ( S a ) values of the samples are accurately predicted by the chemical bonding parameter ( f c ). The results of the correlation between the UC luminescence properties and the microscopic crystal structure, and the relationship of the temperature sensitivity and the host parameters, provide us with a guiding insight for the selection of a host material with ideal temperature measurement capability.

Construction of novel luminescent thermometers based on dual-emission centers of rare-earth and bismuth ions.

Optical thermometry based on fluorescence intensity ratio (FIR) technology has several advantages for industrial and medical applications such as remote signaling, non-invasiveness, and excellent spatial resolution. Here, an approach to the construction of luminescent thermometers is proposed based on high-temperature solid-state reactions through doping of rare earth (RE) elements (e.g., samarium (Sm3+) or europium (Eu3+)) into Ca2Y0.97Bi0.03SbO6 (CYBS) phosphors. The tuning of the CYBS:Eu3+ and CYBS:Sm3+ ratios in the phosphors provided a wide range of color changes from purplish blue to red and from purplish blue to pink, respectively. The superiority of optical thermometer is validated by higher values of absolute sensitivity (Sa) and relative sensitivity (Sr). As such, both phosphors exhibit excellent temperature sensing performance with Sa/Sr values (at 483K) of 4.945×10-2/0.968×10-2K-1 (CYBS:0.05Eu3+) and 2.964×10-2/0.864×10-2K-1 (CYBS:0.05Sm3+). Thus, RE-doped CYBS materials with color tuning properties and superior temperature sensing performance are recommended for the construction of novel luminescent optical thermometers.

A new optical temperature sensor based on the fluorescence intensity ratio of Mn2+ and Mn4+

AbstractIn the course of preparing Mn‐doped phosphors, the mix‐valence state of Mnn+ ions may be obtained with associated interesting properties. This work prepared a new phosphor Ba3MgSb2O9:Mn (BMS:Mn) by a traditional high‐temperature solid‐state synthesis method. In this structure, Mnn+ can replace Mg2+ site as Mn2+ oxidation state or Sb5+ site as Mn4+. Moreover, the emitting bands of Mn2+ and Mn4+ at around 596 and 758 nm are simultaneously observed by using 350 nm as exciting wavelength. Interestingly, the temperature‐dependent emitting intensities corresponding to Mn2+ and Mn4+ are different at temperatures from 10 to 300 K. With increasing temperature, the intensity of Mn2+ luminescence has some enhancement at 10–200 K and then decreases gradually, whereas Mn4+ luminescence goes into rapid decline. By using this character, BMS:0.01Mn can be used as an optical temperature sensor at 10–300 K based on the fluorescence intensity ratio of Mn2+ and Mn4+. The maximum relative sensitivity (Sr) at 125 K is as high as 1.51% K−1.

Temperature sensing and bioimaging realized in NaErF4:40%Tm@NaYF4 with extremely intense red upconversion and suitable R/G emission ratio

The practical application of light thermometer based on the FIR (520/540) has been greatly limited due to the strong absorption of green light by biological tissues. The sensitivity of the temperature sensor located in a biological window (FIR-BW) also needs to be improved. Based on this, we designed and synthesized an upconversion nanoparticles (UCNPs) with suitable R/G ratio and red visual output to prebreaking the limitation of strong absorption of biological tissue, while improving the sensitivity of temperature sensor and in vivo fluorescence imaging. In this paper, NaErF4:40%Tm@NaYF4, a high efficient red UCNPs with R/G ratio (6.86), is first utilized as an optical thermometer, accomplished through the fluorescence intensity ratio (FIR) of thermally coupled stark sublevels of 4S3/2/4F9/2 (FIR(540/654)). In the studied temperature range, the maximum absolute and relative sensitivity (Sa and Sr) is 0.47% K−1 and 2.61% K−1 at 298 K, respectively, which is much higher than most previous reports about FIR-based temperature sensors. Additionally, we investigated the in vivo bioimaging behavior of NaErF4:40%Tm@NaYF4 in detail. The superior biocompatibility, the distribution to the main organs with the blood circulation system, and the bright red fluorescence signals were observed under 980 nm laser radiation. All the results imply that NaErF4:40%Tm@NaYF4 is a promising candidate for optical thermometry and in vivo bioimaging with high sensitivity.

Designing Optical Thermometers Using Down/Upconversion Ca14Al10Zn6O35: Ti4+, Eu3+/Yb3+, Er3+ Thermosensitive Phosphors.

Down/upconversion Ca14Al10Zn6O35 inorganic phosphors codoped with Ti4+/Eu3+ or Yb3+/Er3+ were prepared. The crystal structure and downconversion luminescence properties of Ca14Al10Zn6O35:Ti4+, Eu3+ phosphors were studied in detail. Ti4+ and Eu3+ occupied Al3+ and Ca2+ sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300-570 nm band originated from the 2T2 → O2- transition of Ti4+. The f-f transition of Eu3+ ions generated multiple peaks in the 570-800 nm range. The emission intensity of Ti4+ and Eu3+ ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity (Sr) and the minimum temperature uncertainty (δT) reached 1.41% K-1 and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er3+- and Yb3+-codoped Ca14Al10Zn6O35 phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er3+:2H11/2/4S3/2), the maximum Sr and minimum δT of upconversion phosphors reached 1.28% K-1 and 0.08 K in the temperature range of 293-473 K, respectively. Ca14Al10Zn6O35:Ti4+/Eu3+ (Yb3+/Er3+) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.