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Tm tri-doped Na3ZrF7 upconversion nanocrystals for high performance temperature sensing
Journal of Luminescence 209 (2019) 8–13
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Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Yb/Er/Tm tri-doped Na3ZrF7 upconversion nanocrystals for high performance temperature sensing ⁎
Han Xiaa, Lei Leia,b, , Jienan Xiaa, Youjie Huaa, Degang Denga, Shiqing Xua, a b
T
⁎
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, PR China State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Na3ZrF7 nanocrystals Temperature sensor Self-reference Rare earth ions Upconversion
Non-contact optical thermometry based on fluorescence intensity ratio (FIR) technique has been widely researched over the past few decades. However, the reported systems exhibit two important shortcomings including the existence of a few interferential signals in addition to the required spectral bands for FIR and the absence of internal standard for reference signal. Herein, only two emission bands of Er3+:4F9/2→4I15/2 (~673 nm) and Tm3+:3H4 → 3H6 (~800 nm) are achieved in Yb/Er/Tm tri-doped Na3ZrF7 nano-system. Moreover, the upconversion (UC) emission intensity of Er3+ keeps unchanged with the rising of temperature, which is applied as reference signal; while that of Tm3+ enhances evidently, which is applied as temperature signal. The calculated maximum absolute temperature sensitivity (Sa) and relative temperature sensitivity (Sr) are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K, respectively.
1. Introduction
performance temperature sensing especially without interferential signal. Although using the FIR of green to red in a few Er3+ single activator doped samples could satisfy those conditions, their reference signals varied with temperature and these systems exhibit low absolute temperature sensitivity [17,18]. Phonon represents excited quantum state of crystal structure vibration and its number increases with the rising of temperature. Although the energy level positions of Ln3+ ions are hardly disturbed by external thermal filed owing to the shielding of 4 f electrons by the outer 5s and 5p shells [19], the possibility of electrons non-radiative relaxation to a lower energy level with the assistance of multi-phonon enhances at higher temperature [20], which weakens the fluorescence intensity. On the other hand, heating could activate electrons trapped by defects to an excited state [21,22] and thermal expansion benefit the suppression of energy migration from activators to surface defects [23,24], which will intensify the emission intensity. Hence, it is highly possible to control the temperature dependent fluorescence intensity through tuning the microstructure of UC nanocrystals (NCs) advisably. In another word, adopting unchanged reference signal as internal standard and thermal sensitive one as temperature indicator is an achievable strategy, which guarantees the construction of a perfect ratiometric thermometer. In this work, Na3ZrF7 is chosen as matrix to tri-dope Yb/Er/Tm ions, where Er3+ exhibit single-band red emission and Tm3+ exhibit single-
Non-contact optical thermometry based on FIR technique, which can avoid the affects of external environmental disturbance especially the fluctuation of excitation density, possesses high accuracy for temperature sensing [1–4]. Although lanthanide ions with two thermally coupled energy levels are widely adopted as FIR signals, these systems exhibit large sensing error owing to the distinct overlap of the monitored emission bands with narrow energy gap, as well as low temperature sensitivity [5–9]. To solve this issue, two kinds of activators co-doped downshifting luminescent materials are applied to actualize large temperature dependent FIR variation and distinct spectral separation [10]. However, considering a single lanthanide type generally already exhibits more than two emission bands under one excitation source, co-doping two kinds of lanthanide ions or lanthanide ion and transitional metal ion may generate a few interferential signals in addition to the required spectral bands for FIR. Moreover, the reference signals in these systems are varied with temperature, which are not suitable for internal standards [11–13]. Through modifying electron transition processes, kinds of singleband UC emission systems are achieved in lanthanide-doped fluorides [14–16]. Inspired by this principle, we can design a smart system to achieve dual-only, well separated and different thermal responsive spectral bands, which are the prerequisites for achieving high
⁎
Corresponding authors. E-mail addresses: [email protected] (L. Lei), [email protected] (S. Xu).
https://doi.org/10.1016/j.jlumin.2019.01.024 Received 7 December 2018; Received in revised form 27 December 2018; Accepted 11 January 2019 Available online 14 January 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
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Fig. 1. XRD pattern (a), EDS spectrum (b), TEM (c) and HRTEM (d) images of the 20Yb/2Er/0.5Tm: Na3ZrF7 NCs. Bars in (a) represent the standard orthogonal Na3ZrF7 phase (No. 12-0562). Cu signal in (b) originate from the copper grid.
was mixed with oleic acid (10 mL), oleylamine (3 mL) and NaOA (1 g) under thorough stirring for 30 min. Then, 1 mL NH4F (3.0 mol/L) aqueous solution was added to the above mixture. After vigorously stirring for another 30 min, the resulted semitransparent homogeneous solution was transferred into a 50 mL stainless Teflon-lined autoclave, sealed and heated at 130 °C for 12 h. The final products were washed with ethanol and cyclohexane for three times, and collected by centrifugation at 10,000 rpm for 5 min. The mean particle size is tuned by changing the NaOA content.
band near-infrared emission. Through tuning the negative thermal quenching effect (TQE), the variation trends of the UC emission intensity of Er3+ versus temperature are well controlled. For the as-prepared 20Yb/1Er/0.5Tm:Na3ZrF7 NCs with mean particle size of 45 nm, the UC emission intensity of Er3+ almost keeps unchanged, while that of Tm3+ increases by ~2.5 times with rising the temperature from 313 to 393 K. Taking the unchanged UC emission intensity of Er3+ as internal standard, the calculated maximum values of the absolute temperature sensitivity Sa and relative temperature sensitivity Sr are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K, respectively. In addition, the lasing induced local temperature variation is investigated quantitatively as well.
2.3. Characterizations X-ray diffraction (XRD) analysis was carried out with a powder diffractometer (Bruker D8 Advance) with a Cu-Kα (λ = 1.5405 Å) radiation. The morphology and the size of the products were characterized by a field emission transmission electron microscopy (TEM, FEI Tecnai G2 F20) equipped with an energy dispersive X-ray spectroscope (EDS, Aztec X-Max 80T). UC emission spectra were recorded on an Edinburgh Instruments FLS920 spectrofluorimeter equipped with an adjustable laser diode (980 nm). Temperature dependent photoluminescence properties were characterized by the above spectrometer equipped with a TAP-02 temperature controller (ORIENT KOJI, China). Decay curves were recorded on an Edinburgh Instruments (EI) FS5 spectrofluorometer equipped with a pulsed 980 nm laser. The lifetimes can be fitted by a bi-exponential decay, as defined below:
2. Experimental 2.1. Materials All chemicals were of analytical grade and were used as received without further purification. Deionized water was used throughout. ZrOCl2·8H2O, Ln(NO3)3·6H2O (Ln˭Tm, Er, Yb), sodium oleate (NaOA), NH4F, oleic acid (OA) and oleylamine (OM) were all supplied by Aladdin Chemical Reagent Company. Cyclohexane and ethanol were purchased from Hangzhou Gaojing Fine Chemical Industry Co., Ltd. 2.2. Method
t
A series of Yb/Er/Tm-doped Na3ZrF7 nanocrystals were successfully synthesized by a simple solvethermal method. Taking 20Yb/2Er/ 0.5Tm: Na3ZrF7 as an example, 0.3875 mmol ZrOCl2·8H2O, 0.1 mmol Yb(NO3)3·6H2O, 0.01 mmol Er(NO3)3·6H2O, 0.025 mmol Tm (NO3)3·6H2O were dissolved in 20 mL ethanol. After that, the solution
t
I = A1 ∙e− τ1 + A2 ∙e− τ2
(1)
where I is the UC luminescence intensity, A1 and A2 are constants, and τ1 and τ2 are the corresponding decay times. The mean lifetimes are calculated by the following equation: 9
Journal of Luminescence 209 (2019) 8–13
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τ=
A1 ∙τ12 + A2 ∙τ22 A1 τ1 + A2 τ2
Na3ZrF7 crystal lattice. As shown in Fig. 2a-b and S2, both single-band emissions centered at 673 nm of Er3+ and 800 nm of Tm3+ are observed in the Yb/Er/ Tm:Na3ZrF7 NCs, which characteristics are independent of the mean particle size and activators doping concentration. The UC emission intensities of Er3+ and Tm3+ decrease with increasing the Tm3+ concentration from 0.1, 0.5 to 1 mol%, and the intensity of Tm3+ decreases less than that of Er3+ (Fig. 2a). Owing to the existence of abundant ladder-like energy levels of Er3+ and Tm3+, increasing any activator content in the present tri-doped systems may induces more non-radiative relaxation processes, which is similar to the concentration quenching effect [27]. In addition, increasing Tm3+ content could enhance its energy absorption amount followed by the improved emission intensity, so the FIR of Tm3+ to Er3+ increases at higher Tm3+ content. Similarly, the UC emission intensity of Tm3+ decreases with increasing the Er3+ concentration from 1, 2–3 mol% and the FIR of Er3+ to Tm3+ increases at higher Er3+ content (Fig. 2b). The UC emission intensity of Er3+ slightly enhances with increasing the Er3+ concentration from 1 to 2 mol% and then almost keeps unchanged with further increasing the Er3+ concentration to 3 mol%, which variation trend is a little different from that of Tm3+ in the situation of tuning Tm3+ content. The energy
(2)
Thermally stimulated luminescence (TSL) measurements were performed using a custom-made measurement setup (SL085, Guangzhou, China). 3. Results and discussion XRD pattern of the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs is shown in Fig. 1a. Evidently, all the diffraction peaks are matches well with the pure tetragonal Na3ZrF7 phase (No. 12-0562) [25,26] and no extra impurity phase is observed. TEM image reveals their mean particle size is about 45 nm (Fig. 1c). High-resolution TEM (HRTEM) image indicates the single-crystalline nature and the d spacing of 0.47 nm is corresponding to the (101) plane (Fig. 1d). EDS result verifies the existence of Na, Zr, F and Yb elements (Fig. 1b). It should be noted that the Tm content is too low to be detected from the EDS detector. With rising the reaction temperature to 180 °C, the impurity hexagonal phase of NaYbF4 emerges (Fig. S1), indicating high temperature promotes the Yb3+ nucleate with Na+ and F- ions alone rather than enter into the
Fig. 2. UC emission spectra of 20Yb/2Er/xTm: Na3ZrF7 (x = 0.1, 0.5, 1) NCs (a) and 20Yb/yEr/0.5Tm: Na3ZrF7 (y = 1, 2, 3) NCs (b) under 980 nm laser excitation; inserts are their corresponding line chart of FIR variation trends. Decay curves of Er3+:673 nm (c) and Tm3+:800 nm (d) in 20Yb/2Er/xTm:Na3ZrF7 NCs and 20Yb/ yEr/0.5Tm:Na3ZrF7 NCs. (e) Log-log plots of UC emission intensity versus pumping power in the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs. (f) Proposed UC energy transfer mechanism between Yb3+ and Er3+/Tm3+. 10
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transfer efficiency from Yb3+:2F5/2 to Er3+:4I11/2 with a narrower energy gap is higher than the process of Yb3+:2F5/2 to Tm3+:3H5, so the UC emission intensity of Er3+ enhances more than that of Tm3+ when rising their doping content separately. The variation trends of the fluorescence lifetimes of Er3+ (540 nm and 673 nm) and Tm3+ (800 nm) ions are consistent with that of UC emission intensity (Fig. 2cd and S3). Because the Tm3+ (or Er3+) emission intensity and lifetime in the Yb/Tm/Er: Na3ZrF7 NCs decreases with the increasing of Er3+ (Tm3+) doping concentration, the energy transfer process between Er3+ and Tm3+ in the present researched system is ignored. Log-log plots of UC emission intensity versus pumping power (Fig. 2e) suggest both the red and near-infrared UC emissions are two-photon absorption processes. It has been reported that Yb/Er and Yb/Tm co-doped Na3ZrF7 NCs respectively [16] exhibit red and near-infrared singleband emissions, which are owing to the high cross-relaxation possibility of Er3+:4F7/2 + 4I11/2 → 2 4F9/2 and Tm3+:1G4 + 3F4 → 3H4 + 3F2. For most Yb/Tm co-doped systems [28–31], the emission intensity at 800 nm is much stronger than that of 476 nm, and the transition of 3 H4→3H6 (800 nm) is belong to 2-photon process. Comparing with those reported systems, the emission intensity ratio of 476–800 nm is further decreased in the Yb/Tm:Na3ZrF7 system. Considering the populated electrons on the 1G4 state for blue emission are already much less than that of 3H4 state for 800 nm emission, the contribution of the cross relaxation 1G4 + 3F4 → 3H4 + 3F2 for the n value of 800 nm is very weak. In another word, the 800 nm emission is mainly belonged to 2-photon process, but also contain very small part of 3-photon process. In this scenario, the n value is still less than 2. To further verify our hypothesis, the 20Yb/0.5Tm:NaGdF4 system is prepared and studied. The 800 nm emission is much stronger than that of blue region, and its n value is about 1.6, which is consistent with the above analysis. The proposed energy transfer mechanism is shown in Fig. 2f. Temperature dependent UC emission property of 20Yb/2Er/ 0.5Tm:Na3ZrF7 NCs is shown in Figs. 3a and 3d. With rising the temperature from 313 to 393 K, the UC emission intensity of Er3+ almost keep unchanged, while that of Tm3+ enhance ~2.5 times. With further rising the temperature from 393 to 433 K, the UC emission intensity of Er3+ increase by 20% and that of Tm3+ still keep enhancing, while both of them turn to decrease when heating the NCs up to 473 K (Fig. S4). Furthermore, the temperature related UC properties of 20Yb/2Er/ 0.5Tm:Na3ZrF7 NCs with different mean particle sizes are studied as well. As shown in Figs. 3b and 3e, the UC emission intensity of Er3+ and
Fig. 4. Schematic illustration of the interior and surface defects related negative TQE (a), multi-phonon assisted non-radiative relaxation (MPR) related positive TQE (b) and interior defects related electron trap and release processes (c). D represents interior defects, S represents surface defects and d represents distance between surface defects and sensitizers. CE represents captured electrons, RE represents released electrons.
Tm3+ activators in the sample with ~25 nm increases simultaneously with rising temperature from 313 to 393 K. However, for the sample with mean particle size above 100 nm, the UC emission intensity of Tm3+ keep enhance within the whole measured temperature range, while that of Er3+ increases from 313 to 353 K and then decreases with further rising temperature to 393 K (Figs. 3c and 3f). In addition, the UC emission intensity variation trends of Er3+ and Tm3+ are very similar before and after annealing at 250 °C for 2 h (Fig. S5). Firstly, introducing appropriate defect energy level via low-valence doping facilitates negative TQE through the processes of trapping electrons by the defects at low temperature and then releasing to the closer excited states at high temperature [21,24]. TSL intensity keeps increasing from around 300–460 K, further revealing the continuous release of trapped electrons upon heating (Fig. S6). Secondly, thermal expansion of the crystal lattice could reduce the possibility of energy migration from sensitizers to surface defects. These two effects synergistically improve the UC emission intensity at higher temperature (Fig. 4a) [23]. Thirdly, multi-phonon assisted non-radiative relaxation possibility increases with the rising of temperature, resulting in the
Fig. 3. Temperature dependent UC emission spectra of 20Yb/2Er/0.5Tm:Na3ZrF7 NCs synthesized with different content of NaOA: 1 g (a), 0.5 g (b) and 2 g (c). (d-f) are their corresponding histograms of UC emission intensity versus temperature for Er3+ and Tm3+. 11
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Fig. 5. Plot of FIR (I800/I673) (a) and calculated temperature sensitivity (b) versus temperature for 20Yb/1Er/0.5Tm:Na3ZrF7 NCs. Table 1 Optical thermometry parameters in typical UC materials. Material
λex (nm)
Sa (K−1)
Sr (%K−1)
Δλ (nm)
Ref.
Yb/Er/Tm: Na3ZrF7 NCs Yb3+/Er3+: KMnF3 Nd3+/Yb3+/Er3+: GdOF@SiO2 Er3+/Yb3+: SrWO4 Yb3+/Er3+: NaGdF4 NaGdF4:Yb3+/Tm3+@Tb3+/Eu3+ Yb3+/Tm3+/Gd3+: NaLuF4 Er glass ceramics
980 980 808 980 980 980 980 980
0.17 0.0113 0.0098 – 0.00365 0.012 – –
1.76 5.7 1.6 1.5 1.29 – 0.29 0.25
127 112 35 22 112 70 13 23
This work [18] [32] [33] [34] [35] [36] [37]
Fig. 6. FIR (I800/I673) versus illuminating time (a) and temperature (b) under different excitation power for the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs.
FIR of I800 to I673 can be fitted well by the equation of FIR = A + Bexp (C/ T) (Fig. 5a), where A, B, C are the related constant for the present researched system. The Sa and Sr are calculated by the formulas of Sa = dFIR/ dT and Sr = Sa / FIR , respectively. The maximum Sa and Sr respectively are 0.17 K−1 at 393 K and 1.76%K−1 at 313 K (Fig. 5b), which are superior to most reported UC temperature sensing systems (Table 1). In addition, the reference or temperature signals generally become very weak at higher temperature in those systems, which is not better for detection. The calculated results for different Er3+/Tm3+ doping contents are shown in Fig. S8 and Table S1. It is well known that illuminating with a 980 nm laser at high excitation power could rise the local temperature of Yb3+-sensitized systems, which may damage the normal bio-tissues or cells. Herein, we apply the 20Yb/2Er/0.5Tm: Na3ZrF7 NCs to study the lasing induced temperature variation quantitatively. As shown in Fig. 6a, the FIR (I800/ I673) values slightly changed within 60 min under the excitation at 300 mW and 500 mW. The FIR value enhances over time evidently with increasing the exaction power (above ~700 mW) and the enhancement degree is lager for the higher excitation power. It should be noted that
decreasing of UC emission intensity (Fig. 4b) [20]. In our previous report [21], we have verified the interior defect energy level is closer to the Tm3+:3H5 state than Er3+:4I11/2 one in the lanthanide-doped Na3ZrF7 NCs, so most electrons releases to the Tm3+:3H5 state priority with the rising of temperature (Fig. 4c). As a result, the negative TQE of Tm3+ ion is much more evident than that of Er3+ one in the Yb/Er/Tm tri-doped situation. In this scenario, supposing the role of interior defects can be ignored for Er3+ in Yb/Er/Tm tri-doped systems and through tuning the size-dependent negative TQE to balance the phonon-related positive TQE, the UC emission intensity of Er3+ will be unchanged with the variation of temperature (Fig. 3a and S7). Utilizing the unchanged UC emission intensity of Er3+ as reference signal and the thermal sensitive Tm3+ as temperature one, the temperature sensitivities of Yb/Er/Tm: Na3ZrF7 NCs with different Er/Tm doping concentrations are analyzed. As shown in Fig. S7, the phenomenon that the UC emission intensity of Er3+ keeps unchanged with the rising of temperature is independent of the Er3+/Tm3+ doping concentration, which further reveal the negative TQE of Er3+ is mainly related to the mean particle size for the situation of co-doping Tm3+ activators. Taking 20Yb/1Er/0.5Tm: Na3ZrF7 NCs as an example, the 12
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the temperature dependent FIR variation trends are almost independent of the excitation power when heating the samples by a temperature controller (Fig. 6b). Based on these lines of FIR versus temperature, the calculated temperature variation is about 27 K when illuminating the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs with a 980 nm laser at 1500 mW for 60 min.
[4] E.J. McLaurin, V.A. Vlaskin, D.R. Gamelin, J. Am. Chem. Soc. 133 (2011) 14978. [5] Y. Gao, F. Huang, H. Lin, J.C. Zhou, J. Xu, Y.S. Wang, Adv. Funct. Mater. 26 (2016) 3139–3145. [6] Y.Y. Tian, Y. Tian, P. Huang, L. Wang, Q.F. Shi, C.E. Cui, Chem. Eng. J. 297 (2016) 26–34. [7] P. Du, L.H. Luo, H.K. Park, J.S. Yu, Chem. Eng. J. 306 (2016) 840–848. [8] A.F. Pereira, K.U. Kumar, W.F. Silva, W.Q. Santos, D. Jaque, C. Jacinto, Sens. Actuators B 213 (2015) 65–71. [9] O.A. Savchuk, J.J. Carvajal, M.C. Pujol, E.W. Barrera, J. Massons, M. Aguilo, F. Diaz, J. Phys. Chem. C. 119 (2015) 18546–18558. [10] D.Q. Chen, S. Liu, Y. Zhou, Z.Y. Wan, P. Huang, Z.G. Ji, J. Mater. Chem. C 4 (2016) 9044–9051. [11] H. Xia, L. Lei, W., Q. Hong, S., Q. Xu, J. Alloy. Compd. 757 (2018) 239–245. [12] Y. Pan, X.J. Xie, Q.W. Huang, C. Gao, Y.B. Wang, L.X. Wang, B.X. Yang, H.Q. Su, L. Huang, W. Huang, Adv. Mater. 30 (2018) 1705256. [13] X.T. Rao, T. Song, J.K. Gao, Y.J. Cui, Y. Yang, C.D. Wu, B.L. Chen, G.D. Qian, J. Am. Chem. Soc. 135 (2013) 15559–15564. [14] J. Wang, F. Wang, C. Wang, Z. Liu, X.G. Liu, Angew. Chem. Int. Ed. 50 (2011) 1. [15] G.J. Gao, D. Busko, R. Joseph, I.A. Howard, A. Turshatov, B.S. Richards, ACS Appl. Mater. Interfaces (2018), https://doi.org/10.1021/acsami.8b11196. [16] J. Song, G.S. Wang, S. Ye, Y.L. Tian, M.Z. Xiong, D. Wang, H.B. Niu, J.L. Qu, J. Alloy. Compd. 658 (2016) 914–919. [17] M.Z. Li, Y. Shi, C.Z. Zhao, F.M. Yang, Q.Y. Li, X.X. Zhang, S.C. Wu, H.Y. Chen, J.M. Liu, T. Wei, Dalton Trans. 47 (2018) 11337–11354. [18] X.S. Cui, Y. Cheng, H. Lin, F. Huang, Q.P. Wu, J. Xu, Y.S. Wang, Sens. Actuators B 256 (2018) 498–503. [19] G.Y. Chen, C.H. Yang, P.N. Prasad, Acc. Chem. Res. 46 (2013) 1474–1486. [20] H.M. Zhu, C.C. Lin, W.Q. Luo, S.T. Shu, Z.G. Liu, Y.S. Liu, J.T. Kong, E. Ma, Y.G. Cao, R.S. Liu, X.Y. Chen, Nat. Commun. 5 (2014) 4312. [21] L. Lei, D.Q. Chen, C. Li, F. Huang, J.J. Zhang, S.Q. Xu, J. Mater. Chem. C 6 (2018) 5427–5433. [22] Z.W. Pan, Y.Y. Lu, F. Liu, Nat. Mater. 11 (2012) 58–63. [23] X.S. Cui, Y. Cheng, H. Lin, F. Huang, Q.P. Wu, Y.S. Wang, Nanoscale 9 (2017) 13794–13799. [24] L. Lei, J.N. Xia, Y. Cheng, Y.S. Wang, G.X. Bai, H. Xia, S.Q. Xu, J. Mater. Chem. C 6 (2018) 11587–11592. [25] H.H. Fu, Y.S. Liu, F.L. Jiang, M.C. Hong, Chin. J. Struct. Chem. 11 (2018) 1737–1748. [26] H.H. Fu, P.F. Peng, R.F. Li, C.P. Liu, Y.S. Liu, F.L. Jiang, M.C. Hong, X.Y. Chen, Nanoscale 10 (2018) 9353–9359. [27] N.J.J. Johnson, S. He, S. Diao, E.M. Chan, H.J. Dai, A. Almutairi, J. Am. Chem. Soc. 139 (2017) 3275–3282. [28] T.P. Mokoena, E.C. Linganiso, V. Kumar, H.C. Swart, S. Cho, O.M. Ntwaeaborwa, J. Colloid Interface Sci. 496 (2017) 87–99. [29] J.G. Li, Z.H. Wang, Q. Zhu, Z.X. Xu, X.J. Wang, B.N. Kim, X.D. Li, X.D. Sun, J. Am. Ceram. Soc. 101 (2018) 4519–4525. [30] W.P. Chen, F.F. Hu, R.F. Wei, Q.G. Zeng, L.P. Chen, H. Guo, J. Lumin. 192 (2017) 303–309. [31] Y. Tian, F. Lu, M.M. Xing, J.C. Ran, Y. Fu, Y. Peng, X.X. Luo, Opt. Mater. 64 (2017) 58–63. [32] H. Suo, X.Q. Zhao, Z.Y. Zhang, C.F. Guo, ACS Appl. Mater. Interfaces 9 (2017) 43438–43448. [33] A. Pandey, V.K. Rai, V. Kumar, V. Kumar, H.C. Swart, Sens. Actuators B 209 (2015) 352–358. [34] J.M. Wang, H. Lin, Y. Cheng, X.S. Cui, Y. Gao, Z.L. Ji, J. Xu, Y.S. Wang, Sens. Actuators B 278 (2019) 165–171. [35] S.H. Zheng, W.B. Chen, D.Z. Tan, J.J. Zhou, Q.B. Guo, W. Jiang, C. Xu, X.F. Liu, J.R. Qiu, Nanoscale 6 (2014) 5675. [36] K.Z. Zheng, Z.Y. Liu, C.J. Lv, W.P. Qin, J. Mater. Chem. C 1 (2013) 5502. [37] D.Q. Chen, S. Liu, W. Xu, X.Y. Li, J. Mater. Chem. C 5 (2017) 11769–11780.
4. Conclusion A novel noiseless temperature sensor based on Yb/Er/Tm tri-doped Na3ZrF7 UC NCs is successfully prepared by a simple solvothermal method. Under the excitation of 980 nm laser, both single-band emissions of Er3+ and Tm3+ are achieved. Through tuning the negative TQE via modifying the mean particle size, the variation trends of UC emission intensity of Er3+ versus temperature are well controlled. Taking the unchanged UC emission intensity of Er3+ as internal standard and the thermal sensitive Tm3+ as temperature signal, the calculated maximum Sa and Sr respectively are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K in the 20Yb/1Er/0.5Tm:Na3ZrF7 NCs with mean particle size of 45 nm, which are superior to most reported UC temperature sensing systems. The quantitative results of lasing induced temperature variation provide very meaningful information for the application of UC NCs in bio-medical fields. Conflicts of interest The authors declare no competing financial interests. Acknowledgements This work was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LD18F050001, LY17E020007), National Natural Science Foundation of China (No. 51702306) and National Key Research and Development Program of China (2018YFF0215205) Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.jlumin.2019.01.024. References [1] A.W. Zhu, Q. Qu, X.L. Shao, B. Kong, Y. Tian, Angew. Chem. 124 (2012) 1–6. [2] D. Wawrzynczyk, A. Bednarkiewicz, M. Nyk, W. Strekb, M. Samoc, Nanoscale 4 (2012) 6959. [3] B. Dong, B.S. Cao, Y.Y. He, Z. Liu, Z.P. Li, Z.P. Feng, Adv. Mater. 24 (2012) 1987–1993.
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Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Yb/Er/Tm tri-doped Na3ZrF7 upconversion nanocrystals for high performance temperature sensing ⁎
Han Xiaa, Lei Leia,b, , Jienan Xiaa, Youjie Huaa, Degang Denga, Shiqing Xua, a b
T
⁎
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, PR China State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Na3ZrF7 nanocrystals Temperature sensor Self-reference Rare earth ions Upconversion
Non-contact optical thermometry based on fluorescence intensity ratio (FIR) technique has been widely researched over the past few decades. However, the reported systems exhibit two important shortcomings including the existence of a few interferential signals in addition to the required spectral bands for FIR and the absence of internal standard for reference signal. Herein, only two emission bands of Er3+:4F9/2→4I15/2 (~673 nm) and Tm3+:3H4 → 3H6 (~800 nm) are achieved in Yb/Er/Tm tri-doped Na3ZrF7 nano-system. Moreover, the upconversion (UC) emission intensity of Er3+ keeps unchanged with the rising of temperature, which is applied as reference signal; while that of Tm3+ enhances evidently, which is applied as temperature signal. The calculated maximum absolute temperature sensitivity (Sa) and relative temperature sensitivity (Sr) are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K, respectively.
1. Introduction
performance temperature sensing especially without interferential signal. Although using the FIR of green to red in a few Er3+ single activator doped samples could satisfy those conditions, their reference signals varied with temperature and these systems exhibit low absolute temperature sensitivity [17,18]. Phonon represents excited quantum state of crystal structure vibration and its number increases with the rising of temperature. Although the energy level positions of Ln3+ ions are hardly disturbed by external thermal filed owing to the shielding of 4 f electrons by the outer 5s and 5p shells [19], the possibility of electrons non-radiative relaxation to a lower energy level with the assistance of multi-phonon enhances at higher temperature [20], which weakens the fluorescence intensity. On the other hand, heating could activate electrons trapped by defects to an excited state [21,22] and thermal expansion benefit the suppression of energy migration from activators to surface defects [23,24], which will intensify the emission intensity. Hence, it is highly possible to control the temperature dependent fluorescence intensity through tuning the microstructure of UC nanocrystals (NCs) advisably. In another word, adopting unchanged reference signal as internal standard and thermal sensitive one as temperature indicator is an achievable strategy, which guarantees the construction of a perfect ratiometric thermometer. In this work, Na3ZrF7 is chosen as matrix to tri-dope Yb/Er/Tm ions, where Er3+ exhibit single-band red emission and Tm3+ exhibit single-
Non-contact optical thermometry based on FIR technique, which can avoid the affects of external environmental disturbance especially the fluctuation of excitation density, possesses high accuracy for temperature sensing [1–4]. Although lanthanide ions with two thermally coupled energy levels are widely adopted as FIR signals, these systems exhibit large sensing error owing to the distinct overlap of the monitored emission bands with narrow energy gap, as well as low temperature sensitivity [5–9]. To solve this issue, two kinds of activators co-doped downshifting luminescent materials are applied to actualize large temperature dependent FIR variation and distinct spectral separation [10]. However, considering a single lanthanide type generally already exhibits more than two emission bands under one excitation source, co-doping two kinds of lanthanide ions or lanthanide ion and transitional metal ion may generate a few interferential signals in addition to the required spectral bands for FIR. Moreover, the reference signals in these systems are varied with temperature, which are not suitable for internal standards [11–13]. Through modifying electron transition processes, kinds of singleband UC emission systems are achieved in lanthanide-doped fluorides [14–16]. Inspired by this principle, we can design a smart system to achieve dual-only, well separated and different thermal responsive spectral bands, which are the prerequisites for achieving high
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Corresponding authors. E-mail addresses: [email protected] (L. Lei), [email protected] (S. Xu).
https://doi.org/10.1016/j.jlumin.2019.01.024 Received 7 December 2018; Received in revised form 27 December 2018; Accepted 11 January 2019 Available online 14 January 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
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Fig. 1. XRD pattern (a), EDS spectrum (b), TEM (c) and HRTEM (d) images of the 20Yb/2Er/0.5Tm: Na3ZrF7 NCs. Bars in (a) represent the standard orthogonal Na3ZrF7 phase (No. 12-0562). Cu signal in (b) originate from the copper grid.
was mixed with oleic acid (10 mL), oleylamine (3 mL) and NaOA (1 g) under thorough stirring for 30 min. Then, 1 mL NH4F (3.0 mol/L) aqueous solution was added to the above mixture. After vigorously stirring for another 30 min, the resulted semitransparent homogeneous solution was transferred into a 50 mL stainless Teflon-lined autoclave, sealed and heated at 130 °C for 12 h. The final products were washed with ethanol and cyclohexane for three times, and collected by centrifugation at 10,000 rpm for 5 min. The mean particle size is tuned by changing the NaOA content.
band near-infrared emission. Through tuning the negative thermal quenching effect (TQE), the variation trends of the UC emission intensity of Er3+ versus temperature are well controlled. For the as-prepared 20Yb/1Er/0.5Tm:Na3ZrF7 NCs with mean particle size of 45 nm, the UC emission intensity of Er3+ almost keeps unchanged, while that of Tm3+ increases by ~2.5 times with rising the temperature from 313 to 393 K. Taking the unchanged UC emission intensity of Er3+ as internal standard, the calculated maximum values of the absolute temperature sensitivity Sa and relative temperature sensitivity Sr are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K, respectively. In addition, the lasing induced local temperature variation is investigated quantitatively as well.
2.3. Characterizations X-ray diffraction (XRD) analysis was carried out with a powder diffractometer (Bruker D8 Advance) with a Cu-Kα (λ = 1.5405 Å) radiation. The morphology and the size of the products were characterized by a field emission transmission electron microscopy (TEM, FEI Tecnai G2 F20) equipped with an energy dispersive X-ray spectroscope (EDS, Aztec X-Max 80T). UC emission spectra were recorded on an Edinburgh Instruments FLS920 spectrofluorimeter equipped with an adjustable laser diode (980 nm). Temperature dependent photoluminescence properties were characterized by the above spectrometer equipped with a TAP-02 temperature controller (ORIENT KOJI, China). Decay curves were recorded on an Edinburgh Instruments (EI) FS5 spectrofluorometer equipped with a pulsed 980 nm laser. The lifetimes can be fitted by a bi-exponential decay, as defined below:
2. Experimental 2.1. Materials All chemicals were of analytical grade and were used as received without further purification. Deionized water was used throughout. ZrOCl2·8H2O, Ln(NO3)3·6H2O (Ln˭Tm, Er, Yb), sodium oleate (NaOA), NH4F, oleic acid (OA) and oleylamine (OM) were all supplied by Aladdin Chemical Reagent Company. Cyclohexane and ethanol were purchased from Hangzhou Gaojing Fine Chemical Industry Co., Ltd. 2.2. Method
t
A series of Yb/Er/Tm-doped Na3ZrF7 nanocrystals were successfully synthesized by a simple solvethermal method. Taking 20Yb/2Er/ 0.5Tm: Na3ZrF7 as an example, 0.3875 mmol ZrOCl2·8H2O, 0.1 mmol Yb(NO3)3·6H2O, 0.01 mmol Er(NO3)3·6H2O, 0.025 mmol Tm (NO3)3·6H2O were dissolved in 20 mL ethanol. After that, the solution
t
I = A1 ∙e− τ1 + A2 ∙e− τ2
(1)
where I is the UC luminescence intensity, A1 and A2 are constants, and τ1 and τ2 are the corresponding decay times. The mean lifetimes are calculated by the following equation: 9
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τ=
A1 ∙τ12 + A2 ∙τ22 A1 τ1 + A2 τ2
Na3ZrF7 crystal lattice. As shown in Fig. 2a-b and S2, both single-band emissions centered at 673 nm of Er3+ and 800 nm of Tm3+ are observed in the Yb/Er/ Tm:Na3ZrF7 NCs, which characteristics are independent of the mean particle size and activators doping concentration. The UC emission intensities of Er3+ and Tm3+ decrease with increasing the Tm3+ concentration from 0.1, 0.5 to 1 mol%, and the intensity of Tm3+ decreases less than that of Er3+ (Fig. 2a). Owing to the existence of abundant ladder-like energy levels of Er3+ and Tm3+, increasing any activator content in the present tri-doped systems may induces more non-radiative relaxation processes, which is similar to the concentration quenching effect [27]. In addition, increasing Tm3+ content could enhance its energy absorption amount followed by the improved emission intensity, so the FIR of Tm3+ to Er3+ increases at higher Tm3+ content. Similarly, the UC emission intensity of Tm3+ decreases with increasing the Er3+ concentration from 1, 2–3 mol% and the FIR of Er3+ to Tm3+ increases at higher Er3+ content (Fig. 2b). The UC emission intensity of Er3+ slightly enhances with increasing the Er3+ concentration from 1 to 2 mol% and then almost keeps unchanged with further increasing the Er3+ concentration to 3 mol%, which variation trend is a little different from that of Tm3+ in the situation of tuning Tm3+ content. The energy
(2)
Thermally stimulated luminescence (TSL) measurements were performed using a custom-made measurement setup (SL085, Guangzhou, China). 3. Results and discussion XRD pattern of the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs is shown in Fig. 1a. Evidently, all the diffraction peaks are matches well with the pure tetragonal Na3ZrF7 phase (No. 12-0562) [25,26] and no extra impurity phase is observed. TEM image reveals their mean particle size is about 45 nm (Fig. 1c). High-resolution TEM (HRTEM) image indicates the single-crystalline nature and the d spacing of 0.47 nm is corresponding to the (101) plane (Fig. 1d). EDS result verifies the existence of Na, Zr, F and Yb elements (Fig. 1b). It should be noted that the Tm content is too low to be detected from the EDS detector. With rising the reaction temperature to 180 °C, the impurity hexagonal phase of NaYbF4 emerges (Fig. S1), indicating high temperature promotes the Yb3+ nucleate with Na+ and F- ions alone rather than enter into the
Fig. 2. UC emission spectra of 20Yb/2Er/xTm: Na3ZrF7 (x = 0.1, 0.5, 1) NCs (a) and 20Yb/yEr/0.5Tm: Na3ZrF7 (y = 1, 2, 3) NCs (b) under 980 nm laser excitation; inserts are their corresponding line chart of FIR variation trends. Decay curves of Er3+:673 nm (c) and Tm3+:800 nm (d) in 20Yb/2Er/xTm:Na3ZrF7 NCs and 20Yb/ yEr/0.5Tm:Na3ZrF7 NCs. (e) Log-log plots of UC emission intensity versus pumping power in the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs. (f) Proposed UC energy transfer mechanism between Yb3+ and Er3+/Tm3+. 10
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transfer efficiency from Yb3+:2F5/2 to Er3+:4I11/2 with a narrower energy gap is higher than the process of Yb3+:2F5/2 to Tm3+:3H5, so the UC emission intensity of Er3+ enhances more than that of Tm3+ when rising their doping content separately. The variation trends of the fluorescence lifetimes of Er3+ (540 nm and 673 nm) and Tm3+ (800 nm) ions are consistent with that of UC emission intensity (Fig. 2cd and S3). Because the Tm3+ (or Er3+) emission intensity and lifetime in the Yb/Tm/Er: Na3ZrF7 NCs decreases with the increasing of Er3+ (Tm3+) doping concentration, the energy transfer process between Er3+ and Tm3+ in the present researched system is ignored. Log-log plots of UC emission intensity versus pumping power (Fig. 2e) suggest both the red and near-infrared UC emissions are two-photon absorption processes. It has been reported that Yb/Er and Yb/Tm co-doped Na3ZrF7 NCs respectively [16] exhibit red and near-infrared singleband emissions, which are owing to the high cross-relaxation possibility of Er3+:4F7/2 + 4I11/2 → 2 4F9/2 and Tm3+:1G4 + 3F4 → 3H4 + 3F2. For most Yb/Tm co-doped systems [28–31], the emission intensity at 800 nm is much stronger than that of 476 nm, and the transition of 3 H4→3H6 (800 nm) is belong to 2-photon process. Comparing with those reported systems, the emission intensity ratio of 476–800 nm is further decreased in the Yb/Tm:Na3ZrF7 system. Considering the populated electrons on the 1G4 state for blue emission are already much less than that of 3H4 state for 800 nm emission, the contribution of the cross relaxation 1G4 + 3F4 → 3H4 + 3F2 for the n value of 800 nm is very weak. In another word, the 800 nm emission is mainly belonged to 2-photon process, but also contain very small part of 3-photon process. In this scenario, the n value is still less than 2. To further verify our hypothesis, the 20Yb/0.5Tm:NaGdF4 system is prepared and studied. The 800 nm emission is much stronger than that of blue region, and its n value is about 1.6, which is consistent with the above analysis. The proposed energy transfer mechanism is shown in Fig. 2f. Temperature dependent UC emission property of 20Yb/2Er/ 0.5Tm:Na3ZrF7 NCs is shown in Figs. 3a and 3d. With rising the temperature from 313 to 393 K, the UC emission intensity of Er3+ almost keep unchanged, while that of Tm3+ enhance ~2.5 times. With further rising the temperature from 393 to 433 K, the UC emission intensity of Er3+ increase by 20% and that of Tm3+ still keep enhancing, while both of them turn to decrease when heating the NCs up to 473 K (Fig. S4). Furthermore, the temperature related UC properties of 20Yb/2Er/ 0.5Tm:Na3ZrF7 NCs with different mean particle sizes are studied as well. As shown in Figs. 3b and 3e, the UC emission intensity of Er3+ and
Fig. 4. Schematic illustration of the interior and surface defects related negative TQE (a), multi-phonon assisted non-radiative relaxation (MPR) related positive TQE (b) and interior defects related electron trap and release processes (c). D represents interior defects, S represents surface defects and d represents distance between surface defects and sensitizers. CE represents captured electrons, RE represents released electrons.
Tm3+ activators in the sample with ~25 nm increases simultaneously with rising temperature from 313 to 393 K. However, for the sample with mean particle size above 100 nm, the UC emission intensity of Tm3+ keep enhance within the whole measured temperature range, while that of Er3+ increases from 313 to 353 K and then decreases with further rising temperature to 393 K (Figs. 3c and 3f). In addition, the UC emission intensity variation trends of Er3+ and Tm3+ are very similar before and after annealing at 250 °C for 2 h (Fig. S5). Firstly, introducing appropriate defect energy level via low-valence doping facilitates negative TQE through the processes of trapping electrons by the defects at low temperature and then releasing to the closer excited states at high temperature [21,24]. TSL intensity keeps increasing from around 300–460 K, further revealing the continuous release of trapped electrons upon heating (Fig. S6). Secondly, thermal expansion of the crystal lattice could reduce the possibility of energy migration from sensitizers to surface defects. These two effects synergistically improve the UC emission intensity at higher temperature (Fig. 4a) [23]. Thirdly, multi-phonon assisted non-radiative relaxation possibility increases with the rising of temperature, resulting in the
Fig. 3. Temperature dependent UC emission spectra of 20Yb/2Er/0.5Tm:Na3ZrF7 NCs synthesized with different content of NaOA: 1 g (a), 0.5 g (b) and 2 g (c). (d-f) are their corresponding histograms of UC emission intensity versus temperature for Er3+ and Tm3+. 11
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Fig. 5. Plot of FIR (I800/I673) (a) and calculated temperature sensitivity (b) versus temperature for 20Yb/1Er/0.5Tm:Na3ZrF7 NCs. Table 1 Optical thermometry parameters in typical UC materials. Material
λex (nm)
Sa (K−1)
Sr (%K−1)
Δλ (nm)
Ref.
Yb/Er/Tm: Na3ZrF7 NCs Yb3+/Er3+: KMnF3 Nd3+/Yb3+/Er3+: GdOF@SiO2 Er3+/Yb3+: SrWO4 Yb3+/Er3+: NaGdF4 NaGdF4:Yb3+/Tm3+@Tb3+/Eu3+ Yb3+/Tm3+/Gd3+: NaLuF4 Er glass ceramics
980 980 808 980 980 980 980 980
0.17 0.0113 0.0098 – 0.00365 0.012 – –
1.76 5.7 1.6 1.5 1.29 – 0.29 0.25
127 112 35 22 112 70 13 23
This work [18] [32] [33] [34] [35] [36] [37]
Fig. 6. FIR (I800/I673) versus illuminating time (a) and temperature (b) under different excitation power for the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs.
FIR of I800 to I673 can be fitted well by the equation of FIR = A + Bexp (C/ T) (Fig. 5a), where A, B, C are the related constant for the present researched system. The Sa and Sr are calculated by the formulas of Sa = dFIR/ dT and Sr = Sa / FIR , respectively. The maximum Sa and Sr respectively are 0.17 K−1 at 393 K and 1.76%K−1 at 313 K (Fig. 5b), which are superior to most reported UC temperature sensing systems (Table 1). In addition, the reference or temperature signals generally become very weak at higher temperature in those systems, which is not better for detection. The calculated results for different Er3+/Tm3+ doping contents are shown in Fig. S8 and Table S1. It is well known that illuminating with a 980 nm laser at high excitation power could rise the local temperature of Yb3+-sensitized systems, which may damage the normal bio-tissues or cells. Herein, we apply the 20Yb/2Er/0.5Tm: Na3ZrF7 NCs to study the lasing induced temperature variation quantitatively. As shown in Fig. 6a, the FIR (I800/ I673) values slightly changed within 60 min under the excitation at 300 mW and 500 mW. The FIR value enhances over time evidently with increasing the exaction power (above ~700 mW) and the enhancement degree is lager for the higher excitation power. It should be noted that
decreasing of UC emission intensity (Fig. 4b) [20]. In our previous report [21], we have verified the interior defect energy level is closer to the Tm3+:3H5 state than Er3+:4I11/2 one in the lanthanide-doped Na3ZrF7 NCs, so most electrons releases to the Tm3+:3H5 state priority with the rising of temperature (Fig. 4c). As a result, the negative TQE of Tm3+ ion is much more evident than that of Er3+ one in the Yb/Er/Tm tri-doped situation. In this scenario, supposing the role of interior defects can be ignored for Er3+ in Yb/Er/Tm tri-doped systems and through tuning the size-dependent negative TQE to balance the phonon-related positive TQE, the UC emission intensity of Er3+ will be unchanged with the variation of temperature (Fig. 3a and S7). Utilizing the unchanged UC emission intensity of Er3+ as reference signal and the thermal sensitive Tm3+ as temperature one, the temperature sensitivities of Yb/Er/Tm: Na3ZrF7 NCs with different Er/Tm doping concentrations are analyzed. As shown in Fig. S7, the phenomenon that the UC emission intensity of Er3+ keeps unchanged with the rising of temperature is independent of the Er3+/Tm3+ doping concentration, which further reveal the negative TQE of Er3+ is mainly related to the mean particle size for the situation of co-doping Tm3+ activators. Taking 20Yb/1Er/0.5Tm: Na3ZrF7 NCs as an example, the 12
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the temperature dependent FIR variation trends are almost independent of the excitation power when heating the samples by a temperature controller (Fig. 6b). Based on these lines of FIR versus temperature, the calculated temperature variation is about 27 K when illuminating the 20Yb/2Er/0.5Tm:Na3ZrF7 NCs with a 980 nm laser at 1500 mW for 60 min.
[4] E.J. McLaurin, V.A. Vlaskin, D.R. Gamelin, J. Am. Chem. Soc. 133 (2011) 14978. [5] Y. Gao, F. Huang, H. Lin, J.C. Zhou, J. Xu, Y.S. Wang, Adv. Funct. Mater. 26 (2016) 3139–3145. [6] Y.Y. Tian, Y. Tian, P. Huang, L. Wang, Q.F. Shi, C.E. Cui, Chem. Eng. J. 297 (2016) 26–34. [7] P. Du, L.H. Luo, H.K. Park, J.S. Yu, Chem. Eng. J. 306 (2016) 840–848. [8] A.F. Pereira, K.U. Kumar, W.F. Silva, W.Q. Santos, D. Jaque, C. Jacinto, Sens. Actuators B 213 (2015) 65–71. [9] O.A. Savchuk, J.J. Carvajal, M.C. Pujol, E.W. Barrera, J. Massons, M. Aguilo, F. Diaz, J. Phys. Chem. C. 119 (2015) 18546–18558. [10] D.Q. Chen, S. Liu, Y. Zhou, Z.Y. Wan, P. Huang, Z.G. Ji, J. Mater. Chem. C 4 (2016) 9044–9051. [11] H. Xia, L. Lei, W., Q. Hong, S., Q. Xu, J. Alloy. Compd. 757 (2018) 239–245. [12] Y. Pan, X.J. Xie, Q.W. Huang, C. Gao, Y.B. Wang, L.X. Wang, B.X. Yang, H.Q. Su, L. Huang, W. Huang, Adv. Mater. 30 (2018) 1705256. [13] X.T. Rao, T. Song, J.K. Gao, Y.J. Cui, Y. Yang, C.D. Wu, B.L. Chen, G.D. Qian, J. Am. Chem. Soc. 135 (2013) 15559–15564. [14] J. Wang, F. Wang, C. Wang, Z. Liu, X.G. Liu, Angew. Chem. Int. Ed. 50 (2011) 1. [15] G.J. Gao, D. Busko, R. Joseph, I.A. Howard, A. Turshatov, B.S. Richards, ACS Appl. Mater. Interfaces (2018), https://doi.org/10.1021/acsami.8b11196. [16] J. Song, G.S. Wang, S. Ye, Y.L. Tian, M.Z. Xiong, D. Wang, H.B. Niu, J.L. Qu, J. Alloy. Compd. 658 (2016) 914–919. [17] M.Z. Li, Y. Shi, C.Z. Zhao, F.M. Yang, Q.Y. Li, X.X. Zhang, S.C. Wu, H.Y. Chen, J.M. Liu, T. Wei, Dalton Trans. 47 (2018) 11337–11354. [18] X.S. Cui, Y. Cheng, H. Lin, F. Huang, Q.P. Wu, J. Xu, Y.S. Wang, Sens. Actuators B 256 (2018) 498–503. [19] G.Y. Chen, C.H. Yang, P.N. Prasad, Acc. Chem. Res. 46 (2013) 1474–1486. [20] H.M. Zhu, C.C. Lin, W.Q. Luo, S.T. Shu, Z.G. Liu, Y.S. Liu, J.T. Kong, E. Ma, Y.G. Cao, R.S. Liu, X.Y. Chen, Nat. Commun. 5 (2014) 4312. [21] L. Lei, D.Q. Chen, C. Li, F. Huang, J.J. Zhang, S.Q. Xu, J. Mater. Chem. C 6 (2018) 5427–5433. [22] Z.W. Pan, Y.Y. Lu, F. Liu, Nat. Mater. 11 (2012) 58–63. [23] X.S. Cui, Y. Cheng, H. Lin, F. Huang, Q.P. Wu, Y.S. Wang, Nanoscale 9 (2017) 13794–13799. [24] L. Lei, J.N. Xia, Y. Cheng, Y.S. Wang, G.X. Bai, H. Xia, S.Q. Xu, J. Mater. Chem. C 6 (2018) 11587–11592. [25] H.H. Fu, Y.S. Liu, F.L. Jiang, M.C. Hong, Chin. J. Struct. Chem. 11 (2018) 1737–1748. [26] H.H. Fu, P.F. Peng, R.F. Li, C.P. Liu, Y.S. Liu, F.L. Jiang, M.C. Hong, X.Y. Chen, Nanoscale 10 (2018) 9353–9359. [27] N.J.J. Johnson, S. He, S. Diao, E.M. Chan, H.J. Dai, A. Almutairi, J. Am. Chem. Soc. 139 (2017) 3275–3282. [28] T.P. Mokoena, E.C. Linganiso, V. Kumar, H.C. Swart, S. Cho, O.M. Ntwaeaborwa, J. Colloid Interface Sci. 496 (2017) 87–99. [29] J.G. Li, Z.H. Wang, Q. Zhu, Z.X. Xu, X.J. Wang, B.N. Kim, X.D. Li, X.D. Sun, J. Am. Ceram. Soc. 101 (2018) 4519–4525. [30] W.P. Chen, F.F. Hu, R.F. Wei, Q.G. Zeng, L.P. Chen, H. Guo, J. Lumin. 192 (2017) 303–309. [31] Y. Tian, F. Lu, M.M. Xing, J.C. Ran, Y. Fu, Y. Peng, X.X. Luo, Opt. Mater. 64 (2017) 58–63. [32] H. Suo, X.Q. Zhao, Z.Y. Zhang, C.F. Guo, ACS Appl. Mater. Interfaces 9 (2017) 43438–43448. [33] A. Pandey, V.K. Rai, V. Kumar, V. Kumar, H.C. Swart, Sens. Actuators B 209 (2015) 352–358. [34] J.M. Wang, H. Lin, Y. Cheng, X.S. Cui, Y. Gao, Z.L. Ji, J. Xu, Y.S. Wang, Sens. Actuators B 278 (2019) 165–171. [35] S.H. Zheng, W.B. Chen, D.Z. Tan, J.J. Zhou, Q.B. Guo, W. Jiang, C. Xu, X.F. Liu, J.R. Qiu, Nanoscale 6 (2014) 5675. [36] K.Z. Zheng, Z.Y. Liu, C.J. Lv, W.P. Qin, J. Mater. Chem. C 1 (2013) 5502. [37] D.Q. Chen, S. Liu, W. Xu, X.Y. Li, J. Mater. Chem. C 5 (2017) 11769–11780.
4. Conclusion A novel noiseless temperature sensor based on Yb/Er/Tm tri-doped Na3ZrF7 UC NCs is successfully prepared by a simple solvothermal method. Under the excitation of 980 nm laser, both single-band emissions of Er3+ and Tm3+ are achieved. Through tuning the negative TQE via modifying the mean particle size, the variation trends of UC emission intensity of Er3+ versus temperature are well controlled. Taking the unchanged UC emission intensity of Er3+ as internal standard and the thermal sensitive Tm3+ as temperature signal, the calculated maximum Sa and Sr respectively are 0.17 K−1 at 393 K and 1.76% K−1 at 313 K in the 20Yb/1Er/0.5Tm:Na3ZrF7 NCs with mean particle size of 45 nm, which are superior to most reported UC temperature sensing systems. The quantitative results of lasing induced temperature variation provide very meaningful information for the application of UC NCs in bio-medical fields. Conflicts of interest The authors declare no competing financial interests. Acknowledgements This work was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LD18F050001, LY17E020007), National Natural Science Foundation of China (No. 51702306) and National Key Research and Development Program of China (2018YFF0215205) Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.jlumin.2019.01.024. References [1] A.W. Zhu, Q. Qu, X.L. Shao, B. Kong, Y. Tian, Angew. Chem. 124 (2012) 1–6. [2] D. Wawrzynczyk, A. Bednarkiewicz, M. Nyk, W. Strekb, M. Samoc, Nanoscale 4 (2012) 6959. [3] B. Dong, B.S. Cao, Y.Y. He, Z. Liu, Z.P. Li, Z.P. Feng, Adv. Mater. 24 (2012) 1987–1993.
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