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Ln (Ln = Er, Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals
Journal of the European Ceramic Society 39 (2019) 4275–4282
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Upconversion Luminescence in Yb/Ln (Ln = Er, Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals Yue Liua,1, Wu Chenb,c,1, Jiasong Zhonga, , Daqin Chena,b, ⁎⁎
T
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a
College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou, Zhejiang 310018, China College of Physics and Energy, Fujian Normal University, Fuzhou, Fujian 350117, China c Fujian Provincial Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Xiamen, Fujian, 361005, China b
ARTICLE INFO
ABSTRACT
Keywords: Glass ceramics Perovskite CsPbBr3 Lanthanide Luminescence
Yb/Ln (Ln=Er, Tm) doped TeO2-based glasses containing CsPbBr3 perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr3 exciton recombination under UV excitation, and produce Er3+ green, Er3+ red and Tm3+ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln3+ emissions will be quenched with the precipitation of CsPbBr3 in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr3 rather than energy transfers from Ln3+ to CsPbBr3. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr3 and upconversion luminescence of Er3+ related to pristine ones are retained after immersing the products in water up to 30 days.
1. Introduction Currently, CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (PQDs) or nanocrystals (NCs) have drawn great attentions for their superior optical performance and have shown unprecedented radical progress in optoelectronic field. [1–10] For practical application, the long-term stability of PQDs is one of crucial issues needing consideration. Unfortunately, colloidal PQDs will quickly decompose after exposing in air. [11,12] Recently, CsPbX3 PQDs were successfully incorporated into inorganic oxide glasses (denoted as PQDs@glass), which exhibited excellent water resistance owing to the protecting role of robust glass matrix. [13–17] One of key factors of this strategy is to achieve in-situ nucleation/growth of CsPbX3 crystalline phase among glass matrix via appropriately controlling glass composition/structure and crystallization condition (heat-treatment temperature/time). At present, whole-family CsPbX3 PQDs embedded glasses have been successfully achieved. [18] On the other hand, lanthanide (Ln) doped upconversion (UC) luminescence materials have been extensively investigated to explore their promising applications in display, anti-counterfeiting, optical
thermometry and bio-imaging. [19–23] Tuning UC emissive color is one of key topics and can be routinely achieved by changing hosts and Ln types [24–26]. Recently, UC luminescence of CsPbX3 PQDs beyond the availability of lanthanides has been achieved in the mixed organic solution of CsPbX3 PQDs and Ln-doped UC nanocrystals (UCNCs) upon 980 nm laser excitation, and the energy transfer from UCNCs to PQDs is dominated by a radiative reabsorption process instead of a non-radiative Förster resonance energy transfer (FRET) process. [27,28] Unfortunately, the PQDs in solution are instable with elongation of storing time. In this work, we report the tuning of Ln3+ UC emissive color by interaction between Ln dopants and PQDs, which can be realized by doping Ln3+ ions into CsPbBr3 PQDs embedded glass. As for as we know, there is no report concerning this issue so far. Importantly, benefited from the protecting role of inorganic oxide glass, both downshifting luminescence of PQDs and UC luminescence of Ln3+ dopants in glass exhibit superior long-term stability. 2. Experimental Section Lanthanide-doped glasses containing CsPbBr3 PQDs were prepared
Corresponding author at: College of Physics and Energy, Fujian Normal University, Fuzhou, Fujian 350117, China. Corresponding author. E-mail addresses: [email protected] (J. Zhong), [email protected] (D. Chen). 1 Y. Liu and W. Chen contributed equally. ⁎
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https://doi.org/10.1016/j.jeurceramsoc.2019.06.014 Received 24 May 2019; Received in revised form 4 June 2019; Accepted 6 June 2019 Available online 07 June 2019 0955-2219/ © 2019 Elsevier Ltd. All rights reserved.
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Table 1 TeO2-based oxyhalide glasses containing perovskite-related component and Ln-doped component, and the precipitated phase after crystallization (heat-treatment) at 350 °C for 2 h. The basic glass composition (mol%) of 63TeO2-6B2O3-2Al2O3-15ZnO-14Na2O is 100%, but the total mole content of oxyhalide glass composition is not set to be 100% for better comparison throughout the manuscript. Sample
Basic glass composition (mol%)
Perovskite-related component (mol%)
Ln-doped component (mol%)
Crystallization phase
1 2 3 4 5 6 7 8 9 10
63TeO2-6B2O3-2Al2O3-15ZnO-14Na2O
– 6/12(10CsBr-20PbBr2) 7/12(10CsBr-20PbBr2) 8/12(10CsBr-20PbBr2) 10/12(10CsBr-20PbBr2) 12/12(10CsBr-20PbBr2) – 3/12(10CsBr-20PbBr2) 6/12(10CsBr-20PbBr2) 12/12(10CsBr-20PbBr2)
10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3
– – – – CsPbBr3 CsPbBr3 – – – CsPbBr3
Fig. 1. XRD patterns of (a) the Yb/Er-doped and (b) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component. Photographs of the Yb/Er-doped precursor glass (x = 12/12) and the corresponding CsPbBr3 PQDs@glass nanocomposite under the irradiation of (c) daylight and (d) UV light.
by a traditional melt-quenching and subsequent heat-treatment. Herein, Ln-doped Te-B-Zn-Na-Cs-Pb based oxyhalide glass was designed with the compositions of TeO2-B2O3-Al2O3-ZnO-Na2O-CsBr-PbBr2-YbF3-LnF3 (Ln = Er, Tm), as tabulated in Table 1. The raw materials were mixed well and ground into powders for a certain of time, and melted in a muffle furnace at 800℃ for 30 min under ambient atmosphere to achieve precursor glass. Finally, Ln-doped PQDs@glass was obtained through in-situ glass crystallization via heat-treatment at 350 °C for 2 h, which was determined by differential scanning calorimeter (DSC) analysis (Fig. S1). As a comparison, Mn-doped blank glasses with compositions of TeO2-B2O3-ZnO-Na2O-YbF3-LnF3 was prepared via a similar procedure. DSC trace was recorded at a heating rates of 10 K/min in a simultaneous thermal analyzer (STA449C NETASCH) to follow the thermal behavior of glass. X-ray diffraction (XRD) analysis was carried out to identify the phase structure of the as-prepared samples using a powder diffractometer (MiniFlex600 RIGAKU) with Cu Kα radiation (λ = 0.154 nm) operating at 40 kV. Fourier transform infrared (FTIR) spectra were measured via a Perkin-Elmer IR spectrometer using the KBr pellet technique. Raman spectra were determined by a LabRam HR Raman spectrometer operated with 633 nm as excitation source. Microstructure observations of Ln-doped PQDs@glass were carried out
on a FEI aberration-corrected Titan Cubed S-Twin scanning transmission electron microscope (STEM) operated on a HAADF mode. Photoluminescence (PL), PL excitation (PLE) and UC emission spectra for the Ln-doped PQDs@glass nanocomposites were recorded on an Edinburgh Instruments (EI) FS5 spectra fluorometer equipped with continuous (150 W), pulsed xenon lamps and 980 nm laser diode. Timeresolved PL traces for exciton emission were detected on a fluorescent lifetime spectrometer (Edinburgh Instruments, LifeSpec-II) based on a time correlated single photon counting technique under the excitation of 375 nm picosecond laser. UC decay curves were recorded with a customized UV to mid-infrared steady-state and phosphorescence lifetime spectrometer (FSP920-C, Edinburgh). 3. Results and Discussion XRD patterns of Yb/Er-doped glasses with introduction of different contents of perovskite-related component [x(10CsBr-20PbBr2), x = 0, 6/12, 7/12, 8/12, 10/12, 12/12] and heat-treatment at 350 °C for 2 h are presented in Fig. 1a. Evidently, the blank sample (x = 0) is indeed amorphous structure and pure cubic CsPbBr3 phase (JCPDS No. 540752) is precipitated from glass matrix via glass crystallization only after the perovskite-related components reaches 8/12. Similarly, for the 4276
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Fig. 2. (a) HAADF-STEM image of the Yb/Er-doped CsPbBr3 PQDs@glass nanocomposite (x = 12/12) and (b) HRTEM micrograph of an individual PQD particle. (c) Histogram of PQD size distribution in glass.
Fig. 3. (a) FTIR and (b) Raman (λex = 633 nm) spectra of the Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component (x = 0, 3/12, 6/12, 12/12).
Yb/Tm-doped samples, cubic CsPbBr3 crystals can be in-situ crystallized in glass when the perovskite-related component is high enough (Fig. 1b). As demonstrated in Fig. 1c, the precursor glass with the addition of perovskite-related component (x = 12/12) is transparent and colorless. After glass crystallization, the sample turn to light yellow, confirming the successful growth of CsPbBr3 particles among glass matrix. Indeed, under the irradiation of UV light, the CsPbBr3@glass nanocomposite yields bright green luminescence (Fig. 1d). HAADF-STEM observation, being sensitive to the atomic number (Z) difference in the product, is performed to characterize the prepared PQDs@glass. As exhibited in Fig. 2a, obvious contrast for the CsPbBr3 NCs (bright) and the glass matrix (dark) is distinctly discerned because
of the large difference of atomic number between Cs/Pb/Br (Z = 55/ 82/35) and Te/B/O (Z = 52/5/8), further verifying the successful precipitation of PQDs from the TeO2-based inorganic glass. High-resolution TEM (HRTEM) micrograph (Fig. 2b) verifies the single-crystalline nature of CsPbBr3 with high-crystallinity and distinctly resolved lattice fringes. As shown in Fig. 2c, histogram of PQD size distribution in glass was obtained by measuring the sizes of 200 particles in the HAADF-STEM image. Notably, the sizes of CsPbBr3 NCs are not uniform and are in a broad range of 1˜10 nm (Fig. 2c), which is probably attributed to the impeding role of glass matrix for the growth of CsPbBr3 NCs. FTIR spectra of Yb/Tm-doped samples in the wavenumber of 4277
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Fig. 4. PL spectra (λex = 365 nm) of (a) the Yb/Er-doped and (b) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskiterelated component. (c) PLE spectra and (d) PL decay curves of the Yb/Tm-doped CsPbBr3 PQDs@glass (x = 12/12) by monitoring various emitting wavelengths. The solid curves in (d) are the bi-exponential fitting ones. (e) Two-dimensional wavelength-dependent time-resolved decays for the Yb/Tm-doped CsPbBr3 PQDs@glass (x = 12/12) in the wavelength range of.450–570 nm.
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Fig. 5. UC emission spectra and color coordinates in CIE diagrams for (a, c) the Yb/Er-doped and (b, d) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component. UC emissive photographs for (e) the corresponding Yb/Er and (f) Yb/Tm doped glasses (from left to right: increase of perovskite-related component).
400˜1600 cm−1 (Fig. 3a) show intense stretching vibration of TeeO bonds in TeO4trigonal bipyramids (500˜800 cm−1), stretching vibration of BeO bonds in BO4 units (800˜1200 cm−1) and stretching vibration of BeO bonds in BO3 units (1200˜1600 cm−1), respectively, [29,30] confirming that glass network structure mainly consists of [TeO4], [BO4] and [BO3] units. As a supplement, Raman spectra of the corresponding samples were recorded to trace the structural variation with increase of perovskite-related component content. As shown in Fig. 3b, the blank sample exhibits strong peaks at around 770 cm−1 and 680 cm−1 assigned to stretching vibrations in [TeO3] and [TeO4] groups, respectively. The Raman band at 470 cm−1 is usually ascribed to bending vibrations of TeeOeTe linkages, which are formed by vertex sharing of [TeO4] and [TeO3] polyhedra. [31,32] Notably, two
extra Raman signals at 75 cm-1 and 320 cm-1, attributing to the secondorder phonon mode of the [PbBr6]4- octahedron and the motion of Cs+ cations in CsPbBr3, [33,34] are clearly discerned for the PQDs@glass sample with high-content perovskite-related component (x = 12/12), confirming the growth of CsPbBr3 NCs among glass matrix. We further studied the optical properties of Yb/Ln-doped glasses. As evidenced in Fig. 4a, no obvious emission signal was detected in PL spectra for the Yb/Er-doped samples without or with low-content perovskite-related component (x = 0˜7/12), while a green downshifting emission occurs when perovskite-related component reaches 8/12 and the luminescence intensifies with increase of perovskite-related component. Similar results can be found for the Yb/Tm-doped samples (Fig. 4b). Notably, the luminescence of CsPbBr3 PQDs@glass consists of 4279
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Fig. 6. UC decay curves for the Yb/Er-doped and Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component by monitoring (a) Er3+: 2H11/2, (b) Tm3+: 1G4 and (c) Er3+: 4F9/2 (top), Tm3+: 3H4 (bottom) emissions. (d) Absorption spectra of CsPbBr3 PQDs and UC emission spectra of Er3+ and Tm3+ in glasses, showing the overlap between Er3+ green (Tm3+ blue) UC emission with CsPbBr3 band-to-band absorption. (e) The proposed energy transfer UC processes and reabsorption effect induced by the precipitation of CsPbBr3 PQDs in glass.
three emission bands located at about 470 nm, 520 nm and 540 nm, respectively. PL excitation (PLE) spectra by monitoring different emission wavelengths show similar band-to-band absorption transitions (Fig. 4c), confirming that all these emissions are originated from
exciton recombination of CsPbBr3 PQDs with different particle sizes. CsPbBr3 PQDs exhibited obvious size-dependent luminescence due to quantum confinement effect. [1] With decrease of PQD size, the bandgap will be enlarged, leading to short-wavelength emission for 4280
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Fig. 7. (a) PL spectra (λex = 365 nm) and (b) UC emission spectra (λex = 980 nm) of the Yb/ Er-doped CsPbBr3 PQDs@glass (x = 12/12) after directly immersing in water for different durations (0, 1, 5, 10, 20 and 30 days). Inset of (a) is the integrated CsPbBr3 PL intensity versus storing duration in water; inset of (b) is the integrated Er3+ UC intensity and UC greento-red ratio versus storing duration in water. Luminescence photographs of the corresponding sample immersing in water with elongation of storing time: (c) under the irradiation of UV light, (d) under the irradiation of 980 nm laser.
PQDs with small size. To further confirm this, PL decay curves by monitoring different emissive wavelengths were recorded, as shown in Fig. 4d. Owing to their non-single-exponential feature, these decay curves were fitted via a bi-exponential function and the fitted results were tabulated in Table S1. The decay lifetime in nanosecond order is one of the characteristics of exciton recombination of PQDs. Interestingly, the shorter-wavelength emission originated from exciton recombination of small PQDs shows fast decay. With increase of emission wavelength, the corresponding decay lifetime is gradually elongated. These results indicate that non-radiative relaxation of charge carriers in small PQDs is more obvious than that in large PQDs. This is reasonable since the small PQDs have more surface defects than large ones and thus show high quenching probability of charge carriers. In addition, the decrease of PQD size will induce the enlarged bandgap, which may lead to the reduced probability of radiative relaxation. [35] Indeed, emission-wavelength-dependent two-dimensional decays (Fig. 4e) are observed, i.e., the decay lifetime becomes longer when the detected emission wavelength is gradually increased from 450 nm to 520 nm, and further increasing emission wavelength from 520 nm to 570 nm will not result in significant change of decay since these long-wavelength emissions are originated from exciton recombination of large CsPbBr3 perovskite particles. UC emission spectra for the Yb/Er-doped and Yb/Tm-doped glasses with different contents of perovskite-related component are recorded and shown in Fig. 5a and b, respectively. Under 980 nm near-infrared (NIR) laser excitation, two green UC emissions attributed to 2H11/ 4 4 4 3+ and 2→ I15/2 (˜530 nm) and S3/2→ I15/2 (˜560 nm) transitions of Er one red UC emission ascribed to Er3+ 4F9/2→4I15/2 transition (˜670 nm) are detected for the Yb/Er-doped samples, and a predominant NIR UC emission assigned to Tm3+ 3H4→3H6 transition (˜800 nm) and a weak blue UC emission ascribed to Tm3+ 1G4→3H6 (˜475 nm) are detected for the Yb/Tm-doped samples. Interestingly, with increase of perovskite-related component (i.e., the precipitated CsPbBr3 content) in glass, the Er3+ green emissions related to red one gradually weakens for the Yb/Er-doped samples and the ˜530 nm emission even disappears when the crystalized CsPbBr3 content in glass is high enough (Fig. 5a). Similarly, the Tm3+ blue emission related to NIR one can be completely quenched for the Yb/Tm-doped samples (Fig. 5b). The tuning of UC emissive colors accompanied by the precipitation of CsPbBr3 PQDs in glass is clearly demonstrated by the change of color coordinates in Commission International de I’Eclairage (CIE) 1931 chromaticity diagram (Fig. 5c,d). As evidenced in Fig. 5e, the UC emitting color of the Yb/Er-doped glasses alters from green-yellow to yellow-red with
increase of CsPbBr3 content and the UC emitting color of the Yb/Tmdoped sample changes from blue to deep red. To shed more light on UC tuning mechanism, UC decay behaviors for the corresponding Yb/Ln doped CsPbBr3@glass samples were investigated. As evidenced in Fig. 6a–c, with the precipitation of CsPbBr3 perovskite NCs in glass, no obvious change of UC decay lifetimes for Er3+: 2H11/2 (530 nm), Tm3+: 1G4 (475 nm), Er3+: 4F9/2 (660 nm) and Tm3+: 3H4 (800 nm) emitting states was observed although the Er3+ green UC emission and the Tm3+ blue UC emission were almost quenched. These results verify that there is no non-radiative energy transfer from Ln3+ to PQDs. Fig. 6d shows the absorption of CsPbBr3 PQDs in glass and the UC emissions of Er3+ and Tm3+. Apparently, significant overlap between band-to-band absorption of CsPbBr3 and Er3+: 2H11/2, 4S3/2→4I15/2 transition (or Tm3+: 1G4→3H6 transition) is observed, indicating that the quenching of Er3+ green and Tm3+ blue UC emissions attributes to radiative reabsorption effect. In the present nanocomposite, the Yb/Ln dopants are located in glass matrix rather than in the CsPbBr3 crystalline lattice since the emission profiles and the UC decay behaviors for Er3+ red emitting state and Tm3+ NIR emitting state (Fig. 6c) are not altered after glass crystallization (i.e., the precipitation of CsPbBr3 PQDs). Therefore, the absence of Ln3+-toPQDs energy transfer is reasonable for the large distances between Ln3+ and PQDs distributed in glass matrix even though the related Ln3+ energy levels and conductive band of CsPbBr3 are well matched. As schematically illustrated in Fig. 6e, UC luminescence and emitting color tuning processes are proposed. After Yb3+ sensitizers are populated through ground state absorption (GSA) upon the excitation of NIR (980 nm) laser, the green-emitting 2H11/2,4S3/2 and red-emitting 4F9/2 states of Er3+ are populated via successive two-step Yb3+→Er3+ energy transfers (ETs), and the NIR-emitting 3H4 and blue-emitting 1G4 states are populated via successive two-step and three-step Yb3+→Tm3+ ETs, respectively. [25] Due to spectral matching between Er3+/Tm3+ emission and CsPbBr3 absorption, Er3+ green luminescence or Tm3+ blue luminescence will be gradually quenched via reabsorption of CsPbBr3 PQDs, leading to tunable UC color luminescence with increase of CsPbBr3 content in glass. Finally, the moisture resistance for the as-prepared Yb/Er-doped CsPbBr3 QDs@glass is investigated by directly immersing the sample in water and recording the related optical properties. As shown in Fig. 7a,b, the Yb/Er-doped CsPbBr3 PQDs@glass retains intense green luminescence under UV light excitation and remains intense red UC luminescence under 980 nm laser excitation after storing in water up to 30 days. The integrated PL and UC intensities (insets of Fig. 7a,b) verify 4281
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that about 95% luminescence related to the pristine one can be remained after immersing in water for 30 days. In addition, the green-tored UC emission ratio is also unchanged with elongation of immersing times in water (insets of Fig. 7b). All these results confirm that inorganic glass host is indeed beneficial to efficiently protect CsPbBr3 PQDs from decomposition by water and stably regulate Ln3+ UC luminescence. As evidenced in Fig. 7c,d, the Yb/Er-doped CsPbBr3 PQDs@glass in water can keep bright green downshifting luminescence and red UC luminescence over a period of 30 days.
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4. Conclusions In summary, we have prepared Yb/Ln (Ln = Er, Tm) doped glasses embedding CsPbBr3 PQDs via a facile in-situ glass crystallization strategy. Bright green luminescence with multi-band emissions and typical decay lifetimes in nanoscale are attributed to exciton recombination radiation of CsPbBr3 PQDs with different particle sizes. Under 980 nm laser excitation, characteristic Er3+ green (2H11/2,4S3/ 4 3+ red (4F9/2→4I15/2), Tm3+ blue (1G4→3H6) and Tm3+ 2→ I15/2), Er NIR (3H4→3H6) UC emissions are detected and interestingly the Er3+ green and Tm3+ blue emissions can be gradually quenched with increase content of the precipitated CsPbBr3 PQDs in glasses. The resulted tunable UC emission color in the nanocomposites is evidenced to originate from reabsorption effect, where the UC emitting photons are actually absorbed by CsPbBr3 PQDs rather than energy transfer to CsPbBr3 PQDs. Benefited from the effective protection of PQDs by inorganic glass from erosion of exterior environment, about 95% of exciton luminescence and Er3+ UC luminescence can be retained after immersing the products in water for 30 days. It is expected that the present work will provide a new route to realize emissive tunability of lanthanide-doped UC materials. Notes The authors declare no competing financial interests. Acknowledgements This research was supported by National Natural Science Foundation of China (51572065). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jeurceramsoc.2019.06. 014. References [1] L. Protesescu, M.I. S. Yakunin, F. Bodnarchuk, R.Caputo Krieg, C.H. Hendon, R.X. Yang, A. Walsh, M.V. Kovalenko, Nanocrystals of cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut, Nano Lett. 15 (2015) 3692–3696. [2] X.M. Li, Y. Wu, S. Zhang, B. Cai, Y. Gu, J. Song, H.B. Zeng, CsPbX3 quantum dots for lighting and displays: room‐temperature synthesis, photoluminescence superiorities, underlying origins and white light‐emitting diodes, Adv. Funct. Mater. 26 (2016) 2435–2445. [3] Q. Zhang, Y.D. Yin, All-inorganic metal halide perovskite nanocrystals: opportunities and challenges, ACS Cent. Sci. 4 (2018) 668–679. [4] H.C. Wang, Z. Bao, H.Y. Tsai, A.C. Tang, R.S. Liu, Perovskite quantum dots and their application in light-emitting diodes, Small. 14 (2018) 1702433. [5] J.Z. Song, J.H. Li, X.M. Li, L.M. Xu, Y.H. Dong, H.B. Zeng, Quantum dot lightemitting diodes based on inorganic perovskite cesium lead halides (CsPbX3), Adv. Mater. 27 (2015) 7162–7167. [6] H.C. Wang, S.Y. Lin, A.C. Tang, B.P. Singh, H.C. Tong, C.Y. Chen, Y.C. Lee, T. Tsai, R.S. Liu, Mesoporous silica particles integrate with all-Inorganic CsPbBr3 perovskite quantum-dot nanocomposite (MP-PQDs) with high stability and wide color gamut used for backlight display, Angew. Chem. Int. Ed. 55 (2016) 7924–7929. [7] C. Sun, Y. Zhang, C. Ruan, C.Y. Yin, X.Y. Wang, Y.D. Wang, W.W. Yu, Efficient and stable white LEDs with silica-coated inorganic perovskite quantum dots, Adv.
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Upconversion Luminescence in Yb/Ln (Ln = Er, Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals Yue Liua,1, Wu Chenb,c,1, Jiasong Zhonga, , Daqin Chena,b, ⁎⁎
T
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a
College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou, Zhejiang 310018, China College of Physics and Energy, Fujian Normal University, Fuzhou, Fujian 350117, China c Fujian Provincial Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Xiamen, Fujian, 361005, China b
ARTICLE INFO
ABSTRACT
Keywords: Glass ceramics Perovskite CsPbBr3 Lanthanide Luminescence
Yb/Ln (Ln=Er, Tm) doped TeO2-based glasses containing CsPbBr3 perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr3 exciton recombination under UV excitation, and produce Er3+ green, Er3+ red and Tm3+ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln3+ emissions will be quenched with the precipitation of CsPbBr3 in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr3 rather than energy transfers from Ln3+ to CsPbBr3. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr3 and upconversion luminescence of Er3+ related to pristine ones are retained after immersing the products in water up to 30 days.
1. Introduction Currently, CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (PQDs) or nanocrystals (NCs) have drawn great attentions for their superior optical performance and have shown unprecedented radical progress in optoelectronic field. [1–10] For practical application, the long-term stability of PQDs is one of crucial issues needing consideration. Unfortunately, colloidal PQDs will quickly decompose after exposing in air. [11,12] Recently, CsPbX3 PQDs were successfully incorporated into inorganic oxide glasses (denoted as PQDs@glass), which exhibited excellent water resistance owing to the protecting role of robust glass matrix. [13–17] One of key factors of this strategy is to achieve in-situ nucleation/growth of CsPbX3 crystalline phase among glass matrix via appropriately controlling glass composition/structure and crystallization condition (heat-treatment temperature/time). At present, whole-family CsPbX3 PQDs embedded glasses have been successfully achieved. [18] On the other hand, lanthanide (Ln) doped upconversion (UC) luminescence materials have been extensively investigated to explore their promising applications in display, anti-counterfeiting, optical
thermometry and bio-imaging. [19–23] Tuning UC emissive color is one of key topics and can be routinely achieved by changing hosts and Ln types [24–26]. Recently, UC luminescence of CsPbX3 PQDs beyond the availability of lanthanides has been achieved in the mixed organic solution of CsPbX3 PQDs and Ln-doped UC nanocrystals (UCNCs) upon 980 nm laser excitation, and the energy transfer from UCNCs to PQDs is dominated by a radiative reabsorption process instead of a non-radiative Förster resonance energy transfer (FRET) process. [27,28] Unfortunately, the PQDs in solution are instable with elongation of storing time. In this work, we report the tuning of Ln3+ UC emissive color by interaction between Ln dopants and PQDs, which can be realized by doping Ln3+ ions into CsPbBr3 PQDs embedded glass. As for as we know, there is no report concerning this issue so far. Importantly, benefited from the protecting role of inorganic oxide glass, both downshifting luminescence of PQDs and UC luminescence of Ln3+ dopants in glass exhibit superior long-term stability. 2. Experimental Section Lanthanide-doped glasses containing CsPbBr3 PQDs were prepared
Corresponding author at: College of Physics and Energy, Fujian Normal University, Fuzhou, Fujian 350117, China. Corresponding author. E-mail addresses: [email protected] (J. Zhong), [email protected] (D. Chen). 1 Y. Liu and W. Chen contributed equally. ⁎
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https://doi.org/10.1016/j.jeurceramsoc.2019.06.014 Received 24 May 2019; Received in revised form 4 June 2019; Accepted 6 June 2019 Available online 07 June 2019 0955-2219/ © 2019 Elsevier Ltd. All rights reserved.
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Table 1 TeO2-based oxyhalide glasses containing perovskite-related component and Ln-doped component, and the precipitated phase after crystallization (heat-treatment) at 350 °C for 2 h. The basic glass composition (mol%) of 63TeO2-6B2O3-2Al2O3-15ZnO-14Na2O is 100%, but the total mole content of oxyhalide glass composition is not set to be 100% for better comparison throughout the manuscript. Sample
Basic glass composition (mol%)
Perovskite-related component (mol%)
Ln-doped component (mol%)
Crystallization phase
1 2 3 4 5 6 7 8 9 10
63TeO2-6B2O3-2Al2O3-15ZnO-14Na2O
– 6/12(10CsBr-20PbBr2) 7/12(10CsBr-20PbBr2) 8/12(10CsBr-20PbBr2) 10/12(10CsBr-20PbBr2) 12/12(10CsBr-20PbBr2) – 3/12(10CsBr-20PbBr2) 6/12(10CsBr-20PbBr2) 12/12(10CsBr-20PbBr2)
10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-1ErF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3 10YbF3-0.1TmF3
– – – – CsPbBr3 CsPbBr3 – – – CsPbBr3
Fig. 1. XRD patterns of (a) the Yb/Er-doped and (b) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component. Photographs of the Yb/Er-doped precursor glass (x = 12/12) and the corresponding CsPbBr3 PQDs@glass nanocomposite under the irradiation of (c) daylight and (d) UV light.
by a traditional melt-quenching and subsequent heat-treatment. Herein, Ln-doped Te-B-Zn-Na-Cs-Pb based oxyhalide glass was designed with the compositions of TeO2-B2O3-Al2O3-ZnO-Na2O-CsBr-PbBr2-YbF3-LnF3 (Ln = Er, Tm), as tabulated in Table 1. The raw materials were mixed well and ground into powders for a certain of time, and melted in a muffle furnace at 800℃ for 30 min under ambient atmosphere to achieve precursor glass. Finally, Ln-doped PQDs@glass was obtained through in-situ glass crystallization via heat-treatment at 350 °C for 2 h, which was determined by differential scanning calorimeter (DSC) analysis (Fig. S1). As a comparison, Mn-doped blank glasses with compositions of TeO2-B2O3-ZnO-Na2O-YbF3-LnF3 was prepared via a similar procedure. DSC trace was recorded at a heating rates of 10 K/min in a simultaneous thermal analyzer (STA449C NETASCH) to follow the thermal behavior of glass. X-ray diffraction (XRD) analysis was carried out to identify the phase structure of the as-prepared samples using a powder diffractometer (MiniFlex600 RIGAKU) with Cu Kα radiation (λ = 0.154 nm) operating at 40 kV. Fourier transform infrared (FTIR) spectra were measured via a Perkin-Elmer IR spectrometer using the KBr pellet technique. Raman spectra were determined by a LabRam HR Raman spectrometer operated with 633 nm as excitation source. Microstructure observations of Ln-doped PQDs@glass were carried out
on a FEI aberration-corrected Titan Cubed S-Twin scanning transmission electron microscope (STEM) operated on a HAADF mode. Photoluminescence (PL), PL excitation (PLE) and UC emission spectra for the Ln-doped PQDs@glass nanocomposites were recorded on an Edinburgh Instruments (EI) FS5 spectra fluorometer equipped with continuous (150 W), pulsed xenon lamps and 980 nm laser diode. Timeresolved PL traces for exciton emission were detected on a fluorescent lifetime spectrometer (Edinburgh Instruments, LifeSpec-II) based on a time correlated single photon counting technique under the excitation of 375 nm picosecond laser. UC decay curves were recorded with a customized UV to mid-infrared steady-state and phosphorescence lifetime spectrometer (FSP920-C, Edinburgh). 3. Results and Discussion XRD patterns of Yb/Er-doped glasses with introduction of different contents of perovskite-related component [x(10CsBr-20PbBr2), x = 0, 6/12, 7/12, 8/12, 10/12, 12/12] and heat-treatment at 350 °C for 2 h are presented in Fig. 1a. Evidently, the blank sample (x = 0) is indeed amorphous structure and pure cubic CsPbBr3 phase (JCPDS No. 540752) is precipitated from glass matrix via glass crystallization only after the perovskite-related components reaches 8/12. Similarly, for the 4276
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Fig. 2. (a) HAADF-STEM image of the Yb/Er-doped CsPbBr3 PQDs@glass nanocomposite (x = 12/12) and (b) HRTEM micrograph of an individual PQD particle. (c) Histogram of PQD size distribution in glass.
Fig. 3. (a) FTIR and (b) Raman (λex = 633 nm) spectra of the Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component (x = 0, 3/12, 6/12, 12/12).
Yb/Tm-doped samples, cubic CsPbBr3 crystals can be in-situ crystallized in glass when the perovskite-related component is high enough (Fig. 1b). As demonstrated in Fig. 1c, the precursor glass with the addition of perovskite-related component (x = 12/12) is transparent and colorless. After glass crystallization, the sample turn to light yellow, confirming the successful growth of CsPbBr3 particles among glass matrix. Indeed, under the irradiation of UV light, the CsPbBr3@glass nanocomposite yields bright green luminescence (Fig. 1d). HAADF-STEM observation, being sensitive to the atomic number (Z) difference in the product, is performed to characterize the prepared PQDs@glass. As exhibited in Fig. 2a, obvious contrast for the CsPbBr3 NCs (bright) and the glass matrix (dark) is distinctly discerned because
of the large difference of atomic number between Cs/Pb/Br (Z = 55/ 82/35) and Te/B/O (Z = 52/5/8), further verifying the successful precipitation of PQDs from the TeO2-based inorganic glass. High-resolution TEM (HRTEM) micrograph (Fig. 2b) verifies the single-crystalline nature of CsPbBr3 with high-crystallinity and distinctly resolved lattice fringes. As shown in Fig. 2c, histogram of PQD size distribution in glass was obtained by measuring the sizes of 200 particles in the HAADF-STEM image. Notably, the sizes of CsPbBr3 NCs are not uniform and are in a broad range of 1˜10 nm (Fig. 2c), which is probably attributed to the impeding role of glass matrix for the growth of CsPbBr3 NCs. FTIR spectra of Yb/Tm-doped samples in the wavenumber of 4277
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Fig. 4. PL spectra (λex = 365 nm) of (a) the Yb/Er-doped and (b) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskiterelated component. (c) PLE spectra and (d) PL decay curves of the Yb/Tm-doped CsPbBr3 PQDs@glass (x = 12/12) by monitoring various emitting wavelengths. The solid curves in (d) are the bi-exponential fitting ones. (e) Two-dimensional wavelength-dependent time-resolved decays for the Yb/Tm-doped CsPbBr3 PQDs@glass (x = 12/12) in the wavelength range of.450–570 nm.
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Fig. 5. UC emission spectra and color coordinates in CIE diagrams for (a, c) the Yb/Er-doped and (b, d) Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component. UC emissive photographs for (e) the corresponding Yb/Er and (f) Yb/Tm doped glasses (from left to right: increase of perovskite-related component).
400˜1600 cm−1 (Fig. 3a) show intense stretching vibration of TeeO bonds in TeO4trigonal bipyramids (500˜800 cm−1), stretching vibration of BeO bonds in BO4 units (800˜1200 cm−1) and stretching vibration of BeO bonds in BO3 units (1200˜1600 cm−1), respectively, [29,30] confirming that glass network structure mainly consists of [TeO4], [BO4] and [BO3] units. As a supplement, Raman spectra of the corresponding samples were recorded to trace the structural variation with increase of perovskite-related component content. As shown in Fig. 3b, the blank sample exhibits strong peaks at around 770 cm−1 and 680 cm−1 assigned to stretching vibrations in [TeO3] and [TeO4] groups, respectively. The Raman band at 470 cm−1 is usually ascribed to bending vibrations of TeeOeTe linkages, which are formed by vertex sharing of [TeO4] and [TeO3] polyhedra. [31,32] Notably, two
extra Raman signals at 75 cm-1 and 320 cm-1, attributing to the secondorder phonon mode of the [PbBr6]4- octahedron and the motion of Cs+ cations in CsPbBr3, [33,34] are clearly discerned for the PQDs@glass sample with high-content perovskite-related component (x = 12/12), confirming the growth of CsPbBr3 NCs among glass matrix. We further studied the optical properties of Yb/Ln-doped glasses. As evidenced in Fig. 4a, no obvious emission signal was detected in PL spectra for the Yb/Er-doped samples without or with low-content perovskite-related component (x = 0˜7/12), while a green downshifting emission occurs when perovskite-related component reaches 8/12 and the luminescence intensifies with increase of perovskite-related component. Similar results can be found for the Yb/Tm-doped samples (Fig. 4b). Notably, the luminescence of CsPbBr3 PQDs@glass consists of 4279
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Fig. 6. UC decay curves for the Yb/Er-doped and Yb/Tm-doped glasses after crystallization at 350 °C for 2 h with different contents of perovskite-related component by monitoring (a) Er3+: 2H11/2, (b) Tm3+: 1G4 and (c) Er3+: 4F9/2 (top), Tm3+: 3H4 (bottom) emissions. (d) Absorption spectra of CsPbBr3 PQDs and UC emission spectra of Er3+ and Tm3+ in glasses, showing the overlap between Er3+ green (Tm3+ blue) UC emission with CsPbBr3 band-to-band absorption. (e) The proposed energy transfer UC processes and reabsorption effect induced by the precipitation of CsPbBr3 PQDs in glass.
three emission bands located at about 470 nm, 520 nm and 540 nm, respectively. PL excitation (PLE) spectra by monitoring different emission wavelengths show similar band-to-band absorption transitions (Fig. 4c), confirming that all these emissions are originated from
exciton recombination of CsPbBr3 PQDs with different particle sizes. CsPbBr3 PQDs exhibited obvious size-dependent luminescence due to quantum confinement effect. [1] With decrease of PQD size, the bandgap will be enlarged, leading to short-wavelength emission for 4280
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Fig. 7. (a) PL spectra (λex = 365 nm) and (b) UC emission spectra (λex = 980 nm) of the Yb/ Er-doped CsPbBr3 PQDs@glass (x = 12/12) after directly immersing in water for different durations (0, 1, 5, 10, 20 and 30 days). Inset of (a) is the integrated CsPbBr3 PL intensity versus storing duration in water; inset of (b) is the integrated Er3+ UC intensity and UC greento-red ratio versus storing duration in water. Luminescence photographs of the corresponding sample immersing in water with elongation of storing time: (c) under the irradiation of UV light, (d) under the irradiation of 980 nm laser.
PQDs with small size. To further confirm this, PL decay curves by monitoring different emissive wavelengths were recorded, as shown in Fig. 4d. Owing to their non-single-exponential feature, these decay curves were fitted via a bi-exponential function and the fitted results were tabulated in Table S1. The decay lifetime in nanosecond order is one of the characteristics of exciton recombination of PQDs. Interestingly, the shorter-wavelength emission originated from exciton recombination of small PQDs shows fast decay. With increase of emission wavelength, the corresponding decay lifetime is gradually elongated. These results indicate that non-radiative relaxation of charge carriers in small PQDs is more obvious than that in large PQDs. This is reasonable since the small PQDs have more surface defects than large ones and thus show high quenching probability of charge carriers. In addition, the decrease of PQD size will induce the enlarged bandgap, which may lead to the reduced probability of radiative relaxation. [35] Indeed, emission-wavelength-dependent two-dimensional decays (Fig. 4e) are observed, i.e., the decay lifetime becomes longer when the detected emission wavelength is gradually increased from 450 nm to 520 nm, and further increasing emission wavelength from 520 nm to 570 nm will not result in significant change of decay since these long-wavelength emissions are originated from exciton recombination of large CsPbBr3 perovskite particles. UC emission spectra for the Yb/Er-doped and Yb/Tm-doped glasses with different contents of perovskite-related component are recorded and shown in Fig. 5a and b, respectively. Under 980 nm near-infrared (NIR) laser excitation, two green UC emissions attributed to 2H11/ 4 4 4 3+ and 2→ I15/2 (˜530 nm) and S3/2→ I15/2 (˜560 nm) transitions of Er one red UC emission ascribed to Er3+ 4F9/2→4I15/2 transition (˜670 nm) are detected for the Yb/Er-doped samples, and a predominant NIR UC emission assigned to Tm3+ 3H4→3H6 transition (˜800 nm) and a weak blue UC emission ascribed to Tm3+ 1G4→3H6 (˜475 nm) are detected for the Yb/Tm-doped samples. Interestingly, with increase of perovskite-related component (i.e., the precipitated CsPbBr3 content) in glass, the Er3+ green emissions related to red one gradually weakens for the Yb/Er-doped samples and the ˜530 nm emission even disappears when the crystalized CsPbBr3 content in glass is high enough (Fig. 5a). Similarly, the Tm3+ blue emission related to NIR one can be completely quenched for the Yb/Tm-doped samples (Fig. 5b). The tuning of UC emissive colors accompanied by the precipitation of CsPbBr3 PQDs in glass is clearly demonstrated by the change of color coordinates in Commission International de I’Eclairage (CIE) 1931 chromaticity diagram (Fig. 5c,d). As evidenced in Fig. 5e, the UC emitting color of the Yb/Er-doped glasses alters from green-yellow to yellow-red with
increase of CsPbBr3 content and the UC emitting color of the Yb/Tmdoped sample changes from blue to deep red. To shed more light on UC tuning mechanism, UC decay behaviors for the corresponding Yb/Ln doped CsPbBr3@glass samples were investigated. As evidenced in Fig. 6a–c, with the precipitation of CsPbBr3 perovskite NCs in glass, no obvious change of UC decay lifetimes for Er3+: 2H11/2 (530 nm), Tm3+: 1G4 (475 nm), Er3+: 4F9/2 (660 nm) and Tm3+: 3H4 (800 nm) emitting states was observed although the Er3+ green UC emission and the Tm3+ blue UC emission were almost quenched. These results verify that there is no non-radiative energy transfer from Ln3+ to PQDs. Fig. 6d shows the absorption of CsPbBr3 PQDs in glass and the UC emissions of Er3+ and Tm3+. Apparently, significant overlap between band-to-band absorption of CsPbBr3 and Er3+: 2H11/2, 4S3/2→4I15/2 transition (or Tm3+: 1G4→3H6 transition) is observed, indicating that the quenching of Er3+ green and Tm3+ blue UC emissions attributes to radiative reabsorption effect. In the present nanocomposite, the Yb/Ln dopants are located in glass matrix rather than in the CsPbBr3 crystalline lattice since the emission profiles and the UC decay behaviors for Er3+ red emitting state and Tm3+ NIR emitting state (Fig. 6c) are not altered after glass crystallization (i.e., the precipitation of CsPbBr3 PQDs). Therefore, the absence of Ln3+-toPQDs energy transfer is reasonable for the large distances between Ln3+ and PQDs distributed in glass matrix even though the related Ln3+ energy levels and conductive band of CsPbBr3 are well matched. As schematically illustrated in Fig. 6e, UC luminescence and emitting color tuning processes are proposed. After Yb3+ sensitizers are populated through ground state absorption (GSA) upon the excitation of NIR (980 nm) laser, the green-emitting 2H11/2,4S3/2 and red-emitting 4F9/2 states of Er3+ are populated via successive two-step Yb3+→Er3+ energy transfers (ETs), and the NIR-emitting 3H4 and blue-emitting 1G4 states are populated via successive two-step and three-step Yb3+→Tm3+ ETs, respectively. [25] Due to spectral matching between Er3+/Tm3+ emission and CsPbBr3 absorption, Er3+ green luminescence or Tm3+ blue luminescence will be gradually quenched via reabsorption of CsPbBr3 PQDs, leading to tunable UC color luminescence with increase of CsPbBr3 content in glass. Finally, the moisture resistance for the as-prepared Yb/Er-doped CsPbBr3 QDs@glass is investigated by directly immersing the sample in water and recording the related optical properties. As shown in Fig. 7a,b, the Yb/Er-doped CsPbBr3 PQDs@glass retains intense green luminescence under UV light excitation and remains intense red UC luminescence under 980 nm laser excitation after storing in water up to 30 days. The integrated PL and UC intensities (insets of Fig. 7a,b) verify 4281
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that about 95% luminescence related to the pristine one can be remained after immersing in water for 30 days. In addition, the green-tored UC emission ratio is also unchanged with elongation of immersing times in water (insets of Fig. 7b). All these results confirm that inorganic glass host is indeed beneficial to efficiently protect CsPbBr3 PQDs from decomposition by water and stably regulate Ln3+ UC luminescence. As evidenced in Fig. 7c,d, the Yb/Er-doped CsPbBr3 PQDs@glass in water can keep bright green downshifting luminescence and red UC luminescence over a period of 30 days.
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4. Conclusions In summary, we have prepared Yb/Ln (Ln = Er, Tm) doped glasses embedding CsPbBr3 PQDs via a facile in-situ glass crystallization strategy. Bright green luminescence with multi-band emissions and typical decay lifetimes in nanoscale are attributed to exciton recombination radiation of CsPbBr3 PQDs with different particle sizes. Under 980 nm laser excitation, characteristic Er3+ green (2H11/2,4S3/ 4 3+ red (4F9/2→4I15/2), Tm3+ blue (1G4→3H6) and Tm3+ 2→ I15/2), Er NIR (3H4→3H6) UC emissions are detected and interestingly the Er3+ green and Tm3+ blue emissions can be gradually quenched with increase content of the precipitated CsPbBr3 PQDs in glasses. The resulted tunable UC emission color in the nanocomposites is evidenced to originate from reabsorption effect, where the UC emitting photons are actually absorbed by CsPbBr3 PQDs rather than energy transfer to CsPbBr3 PQDs. Benefited from the effective protection of PQDs by inorganic glass from erosion of exterior environment, about 95% of exciton luminescence and Er3+ UC luminescence can be retained after immersing the products in water for 30 days. It is expected that the present work will provide a new route to realize emissive tunability of lanthanide-doped UC materials. Notes The authors declare no competing financial interests. Acknowledgements This research was supported by National Natural Science Foundation of China (51572065). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jeurceramsoc.2019.06. 014. References [1] L. Protesescu, M.I. S. Yakunin, F. Bodnarchuk, R.Caputo Krieg, C.H. Hendon, R.X. Yang, A. Walsh, M.V. Kovalenko, Nanocrystals of cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut, Nano Lett. 15 (2015) 3692–3696. [2] X.M. Li, Y. Wu, S. Zhang, B. Cai, Y. Gu, J. Song, H.B. Zeng, CsPbX3 quantum dots for lighting and displays: room‐temperature synthesis, photoluminescence superiorities, underlying origins and white light‐emitting diodes, Adv. Funct. Mater. 26 (2016) 2435–2445. [3] Q. Zhang, Y.D. Yin, All-inorganic metal halide perovskite nanocrystals: opportunities and challenges, ACS Cent. Sci. 4 (2018) 668–679. [4] H.C. Wang, Z. Bao, H.Y. Tsai, A.C. Tang, R.S. Liu, Perovskite quantum dots and their application in light-emitting diodes, Small. 14 (2018) 1702433. [5] J.Z. Song, J.H. Li, X.M. Li, L.M. Xu, Y.H. Dong, H.B. Zeng, Quantum dot lightemitting diodes based on inorganic perovskite cesium lead halides (CsPbX3), Adv. Mater. 27 (2015) 7162–7167. [6] H.C. Wang, S.Y. Lin, A.C. Tang, B.P. Singh, H.C. Tong, C.Y. Chen, Y.C. Lee, T. Tsai, R.S. Liu, Mesoporous silica particles integrate with all-Inorganic CsPbBr3 perovskite quantum-dot nanocomposite (MP-PQDs) with high stability and wide color gamut used for backlight display, Angew. Chem. Int. Ed. 55 (2016) 7924–7929. [7] C. Sun, Y. Zhang, C. Ruan, C.Y. Yin, X.Y. Wang, Y.D. Wang, W.W. Yu, Efficient and stable white LEDs with silica-coated inorganic perovskite quantum dots, Adv.
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