Confining Mn2+-Doped Lead Halide Perovskite in Zeolite-Y as

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Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

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Confining Mn2+-Doped Lead Halide Perovskite in Zeolite‑Y as Ultrastable Orange-Red Phosphor Composites for White LightEmitting Diodes Shi Ye,* Jia-Yi Sun, Yu-Hong Han, Ya-Yun Zhou, and Qin-Yuan Zhang* State Key Laboratory of Luminescent Materials and Devices, Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, South China University of Technology, Guangzhou 510641, China ACS Appl. Mater. Interfaces 2018.10:24656-24664. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 09/20/18. For personal use only.

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ABSTRACT: CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have emerged as competitive candidate luminescent materials in the photoelectric fields due to their superior luminescence properties. However, the major drawback such as poor resistance to temperature, moisture, and irradiation of light, especially for the red QDs with I−, hinders their practical applications. Herein, we synthesized Mn2+-doped CsPbCl3 embedded in the cage of zeolite-Y as a new orange-red phosphor for the white light-emitting diode (WLED). The composites have significantly improved resistance to both elevated temperature and water over the bare Mn2+-doped QDs. The former exhibits little degradation whereas the latter shows apparent decline upon the irradiation of lights in the orange LED devices, which are fabricated by employing each material as a color-conversion phosphor coated on a 365 nm UV chip. A WLED is also achieved with a 365 nm UV chip coated with a CsPb(Cl0.5,Br0.5)3−Y blue phosphor and a CsPb0.75Mn0.25Cl3−Y orange phosphor. The device possesses a Commission Internationale de l’É clairage coordinate of (0.34, 0.36), a correlated color temperature of 5336 K and a color rendering index of 81. KEYWORDS: perovskite quantum dots, Mn2+ doped, zeolites, stability, white LED

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some other report showing that Mn2+ has good compatibility with cations in CsPbCl3 and it provides a new exciton transition pathway to alter the emission.41−43 The resulting orange-red emission of Mn2+ in perovskite QDs makes it as a promising substituent red phosphor for WLEDs. Additionally, there is another merit to use Mn2+ as a dopant in perovskite QDs, that is, it reduces the usage of toxic component Pb2+. Actually, the research on complete or partial substitution of Pb by other less toxic elements besides Mn has been done.44−48 Various methods were reported to prepare Mn2+-doped CsPbX3.40,41,49−5540,41,49−55 It is also reported that further improvement in stability can be achieved for Mn2+-doped CsPbX3 nanostructure constructed through a core−isocrystalline shell structure or silica-coating.56,57 Our previous research evidently demonstrates the improvement in irradiation of light or duration in the air by encapsulating CsPbX3 in porous zeolite.39 Accordingly, confining the Mn2+-doped CsPbCl3 in porous zeolite as an orange-red phosphor would accomplish further improvement in the resistance to elevated temperature, water, and irradiation. In this research, we successfully synthesized Mn2+-doped CsPbX3 perovskite embedded in zeolite-Y (Cs(Pb,Mn)Cl3−Y) by a facile two-step synthesis method. The zeolites were first

INTRODUCTION Recently, all inorganic perovskite (CsPbX3, X = Cl, Br, I) quantum dots (QDs) have attracted much attention and the field is advancing rapidly.1−6 Their outstanding optical properties including high photoluminescence quantum yields, tunable and narrow emissions over the entire visible spectral range, as well as being less sensitive to oxygen and moisture than their hybrid counterparts,7,8 make them particularly promising candidate materials for many applications such as phosphor-converted white light-emitting diodes (WLEDs), lasing, and so on.9−23 Although various studies on CsPbX3 QDs as color-conversion phosphors have made great progress up to now, poor stability is still the main drawback, severely restricting their practical applications,24 especially for the red QDs with I−. In addition to the poor resistance to elevated temperature and moisture,25−35 the anion-mixed red QDs with I− suffer from strong spinodal decomposition thermodynamically upon irradiation of light.36,37 Therefore, great efforts have been devoted to prepare more stable perovskite QDs through various approaches such as embedding QDs in a polymeric matrix like poly(methyl methacrylate) or polystyrene as well as in an inorganic matrix like mesoporous silica or zeolite,1,2,30,38,39 coating with a polymer or silica,24,27,28 high chloride doping in the surface,25 and X-ray lithography on QD films.29 As a matter of fact, doping other cations is supposed to be an alternative way and Mn2+ is experimentally and theoretically proved to be an effective option.40 There is © 2018 American Chemical Society

Received: May 20, 2018 Accepted: July 6, 2018 Published: July 6, 2018 24656

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

with a 0.02 g of CsPb0.75Mn0.25Cl3−Y composite (2.0 mg of bare QDs is used for a comparison device) and the mixture was stirred thoroughly and dried at 60 °C. Afterwards, the phosphor mixture was deposited on a 365 nm UV LED chip and cured at 150 °C. (2) For the WLED device in Figure 7, 0.02 g of silicone resin A and 0.02 g of silicone resin B were mixed with a 0.01 g of CsPb0.75Mn0.25Cl3−Y composite, then 0.01 g of CsPb(Cl0.5,Br0.5)3−Y was added. The mixture was stirred thoroughly and dried at 60 °C. Afterwards, the phosphor mixture was deposited on a 365 nm UV LED chip and cured at 150 °C. Measurement and Characterization. X-ray diffraction (XRD) patterns of the as-synthesized samples were measured on a Rigaku D/ max-IIIA X-ray diffractometer using Cu Kα radiation (λ = 1.5418 Å). Scanning electron microscopy (SEM) images were obtained using a FEI Nova Nano SEM 430 field-emission scanning electron microscope. The transmission electron microscopy (TEM) images were recorded on a JEOL JEM-2100F transmission electron microscope. The high-resolution TEM (HRTEM) images and elemental mapping of resin-embedded sections of CsPb0.62Mn0.38(Cl,Br)3−Y were taken on a FEI Tecnai G2 F30. The inductively coupled plasma optical emission spectrometer measurements of metal elements were carried out on Variance 2000e, whereas the content of N element was obtained by Thermo Fisher Scientific Flash2000. Photoluminescence spectra were recorded on an Edinburgh Instruments FLS 920 spectrometer with a red-sensitive photomultiplier tube (R928), and the temperature-dependent photoluminescence spectra were measured with a temperature controller system. Fluorescence lifetimes were measured using a Hamamatsu Photonics C11367-11. The optical properties of LEDs and WLEDs were obtained using an HAAS2000 integrated sphere with an analyzer system of EVERFINE. The water resistance measurement was performed on the same integrated sphere for those samples deposited on a glass slide, which are immersed in water contained in a glass bottle.

exchanged with Cs+ ions by an ion-exchange reaction from aqueous solution. Afterwards Cs+-exchanged zeolites reacted with PbX2 and MnX2 (with X = Cl, Br, or the mixture of two) ions to form perovskite QDs. The emission of the composites can be adjusted by controlling Mn2+ contents or varying halide ions. Besides the benefit of the reduced toxic lead content, the composites show better resistance to elevated temperatures and water than the bare perovskite QDs. Furthermore, a LED with CsPb0.75Mn0.25Cl3−Y (short for CsPb0.75Mn0.25Cl3− zeolite-Y) as the color-converted material is assembled and exhibits a superior working stability. A WLED is also fabricated by coating a 365 nm UV chip with CsPb(Cl0.5,Br0.5)3−Y and CsPb0.75Mn0.25Cl3−Y as phosphors. The device produces white light with a Commission Internationale de l’É clairage (CIE) coordinate of (0.34, 0.36), a correlated color temperature (CCT) of 5336 K and a color rendering index (CRI) of 81.

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EXPERIMENTAL SECTION

Materials and Chemicals. M+−zeolite-Y (M+ = NH4+, Na+, SiO2/Al2O3 = 5.2 in molar ratio, Alfa Aesar), cesium bromide (CsBr, Alfa Aesar, 99.9%), oleic acid (OA, Aladdin, Analytical Reagent (AR)), 1-octadecene (ODE, Sigma-Aldrich, 90%), oleylamine (OAm, Aladdin, 8090%), lead chloride (PbCl2, Alfa Aesar, 99.999%), lead bromide (PbBr2, Alfa Aesar, 99.999%), manganese chloride (MnCl2, Alfa Aesar, ultra-dry, 99.99%), manganese bromide (MnBr2, Alfa Aesar, anhydrous, 99%), n-trioctylphosphine (TOP, Stream, 97%), nhexane (Aladdin, 97%), isopropanol (AR, Fuyu Chemicals), silicone resin A, and silicone resin B (Dow Corning, OE 6550), and 365 nm UV LED chip (Sanan optoelectronics). All the chemicals were used without further purification. Preparation of Cs+−Y. Zeolite-Y (1.0 g) was dispersed in 10.0 mL aqueous solution of 1.0 mol/L CsBr. Then the mixture was stirred in a water bath at 70 °C for 24 h. The products were centrifuged and washed with deionized water twice, and then dried in air at 80 °C for 12 h. Preparation of PbX2 and MnX2 Solution. A specific molar ratio of PbX2 and MnX2 were mixed with ODE (5.0 mL) in a 50 mL threeneck flask and dried under vacuum for 30 min at 120 °C. OA (2.0 mL) and OAm (2.0 mL) were injected under a N2 atmosphere. After complete dissolution of the PbX2 and MnX2 salts, the solution was naturally cooled down to room temperature under a N2 atmosphere. A higher temperature of 150 °C and the addition of TOP (1.0 mL) were necessary to dissolve PbCl2. Synthesis of Cs(Pb,Mn)X3−Y. First, ODE (5.0 mL) and Cs+−Y (0.5 g) were mixed in a 50 mL three-neck flask, and dried under vacuum for 30 min at 120 °C. Then the temperature was raised to 130−170 °C under a N2 atmosphere followed by the injection of PbX2 and MnX2 solution. The mixture was stirred for approximately 15 min and then cooled down with an ice-water bath. Finally, the product was washed with n-hexane and isopropanol twice and centrifuged. The composites were dried at 60 °C under vacuum for 10 h. Synthesis of Cs(Pb,Mn)Cl3 Perovskite QDs. The Cs-precursor was prepared following a procedure as in ref 2. Specific molar ratios of PbCl2 and MnCl2 were mixed with ODE (5.0 mL) in a 50 mL threeneck flask and dried under vacuum for 30 min at 120 °C. OA (2.0 mL) and OAm (2.0 mL) were injected under a N2 atmosphere. After complete dissolution of the PbCl2 and MnCl2 salts, the temperature was raised to 150 °C and 0.5 mL Cs-precursor was swiftly injected into the mixture. After the reaction for approximately 5 s, the system was cooled down with an ice-water bath. After centrifugation, the products were dispersed in n-hexane. The droplets of Cs(Pb,Mn)Cl3 QDs were deposited on a glass slide to prepare a film for measurement. Synthesis of CsPb(Cl0.5,Br0.5)3−Y. The composite was prepared following the same procedure as in ref 39. Fabrication of LED Devices. (1) For the LED device in Figure 6, 0.02 g of silicone resin A and 0.02 g of silicone resin B were mixed

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RESULTS AND DISCUSSION Synthesis of Cs(Pb,Mn)X3−Y Composites. Cs(Pb,Mn)X3−Y composites are synthesized by a facile two-step in situ synthesis. First, Cs+-exchanged zeolite-Y (Cs+−Y) is prepared with the purchased M+−Y immerged in an aqueous CsBr solution at 60 °C under vigorous stirring. Secondly, the dried Cs+−Y crystals are dispersed in 1-octadecene (ODE) and are allowed to react with an organic solution (OA, oleic acid; OAm, oleylamine) of PbX2 and MnX2 (X = Cl, Br, or a mixture of two) at 130−170 °C for 15 min under a N2 atmosphere (Figure 1). This method can achieve an in situ synthesis of Cs(Pb,Mn)X3 inside the cages of zeolite-Y (eq 1) Cs+ − Y + Pb2 + + Mn 2 + + 3X− → Cs(Pb,Mn)X3 − Y (1)

Composition, Structure, and Morphology. Elemental analysis techniques were used to determine the contents of balanced cation M+ in zeolite before and after the ion-exchange reaction, and the ratio of Pb2+ to Mn2+ in different composites. It can be found in Table 1 that about 60% of balanced cation M+ (M+ = NH4+, Na+) inside the cages of the zeolite is exchanged by the Cs+. Table 2 shows that the deduced Mn2+ content increases as its feed ratio increases. Also, it can be found that for the similar Pb/Mn feed ratio, Mn2+ are more likely to be incorporated into the composites containing both Cl− and Br− ions, rather than those with a single halogen. The contents of the perovskite halides are evaluated by the contents of Pb2+ since there is still some Cs+ unreacted with lead halides according to the previous work.39 Figure 2a shows X-ray diffraction (XRD) patterns of the CsPbxMn1−x(Cl,Br)3−Y composites with different Pb/Mn molar ratios. The diffraction angles of all samples match well 24657

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

Figure 2. (a) X-ray diffraction patterns of the CsPbxMn1−x(Cl,Br)3−Y composites with Pb-to-Mn molar feed ratios of 1:1 (blue), 1:3 (purple), 1:5 (orange), and the JCPDS reference pattern #00-0430168 (black bars). SEM images of (b) the original zeolite-Y, and (c) the CsPb0.62Mn0.38(Cl,Br)3−Y composite.

Figure 1. Schematic illustration of the two-step synthesis of Cs(Pb,Mn)X3−Y composites, involving Cs+ ion-exchange followed by the reaction with PbX2 and MnX2.

two samples is similar, with 0.5−1.0 μm length of sides and smooth surfaces. The embedding of perovskite halides can be directly observed using a transmission electron microscope (TEM). Figure 3a,b shows a TEM image of a CsPb0.62Mn0.38(Cl,Br)3− Y composite grain (was cut into pieces) and its corresponding elemental mapping by means of energy-dispersive X-ray (EDX) spectroscopy. Separate elemental maps are exhibited in Figure S1a,i. Figure 3c is a high-resolution TEM (HRTEM) image of one piece of the grain in Figure 3a. To minimize the collapse of the framework structure of the zeolites caused by the electron beam, the image was recorded within 10 s at a low operating voltage of 120 kV. The lattice fringes are clearly shown in the image spaced by 14.2 Å, corresponding to the spacing of the (111) lattice planes of the faujasite zeolites (JCPDF #00-043-0168). Owing to the instable nature of the zeolite and perovskite halides upon electron beam bombardment, it is quite tough to capture the fingerprints of both at the same time. However, all the chemical elements of CsPb0.62Mn0.38(Cl,Br)3 can be found throughout the crosssection of the zeolite fragment pieces in Figures 3b and S1. More analogous evidences of the perovskites embedded in the zeolites can be referred to our previous report on the undoped perovskite halides in the zeolites.39 It is also proved by the difference of luminescence behavior between the composites and the bare perovskite QDs, which will be discussed in the Photoluminescence Properties section. Photoluminescence Properties. Figure 4a shows the emission spectra of CsPbxMn1−xCl3−Y composites, which are similar to those previously reported for the freely dispersed CsPbxMn1−xCl3 perovskite QDs.41,49,56,58,59 When Mn2+ doping concentration is low, there is only one narrow emission peak at 408 nm with a full width at half-maximum (FWHM) of 10 nm, which is assigned to the exciton emission of perovskite in the composites. With the increase in the Mn2+ content, a broad emission with the FWHM of about 80 nm appears at ∼600 nm, which is derived from the 4T1−6A1 transition of

Table 1. Contents of the Balanced Cation M+ in Zeolites before and after the Ion-Exchange Reaction samples

element

contents (g/kg)

contents (mol/kg)

zeolite-Y

Na(Na+) N(NH4+) Na(Na+) N(NH4+) Cs(Cs+)

15.32 34.20 11.46 6.80 235.67

0.6664 2.4411 0.4985 0.4854 1.7732

Cs−Y

Table 2. Compositions of Different Cs(Pb,Mn)X3−Y Composites chemicals PbCl2/MnCl2

PbBr2/MnCl2

feed ratio

deduced formula

deduced contents of perovskites (mol/kg)

1:1 1:3 1:5 1:1 1:3 1:5

CsPb0.91Mn0.09Cl3−Y CsPb0.81Mn0.19Cl3−Y CsPb0.75Mn0.25Cl3−Y CsPb0.82Mn0.18(Cl,Br)3−Y CsPb0.64Mn0.36(Cl,Br)3−Y CsPb0.62Mn0.38(Cl,Br)3−Y

0.4697 0.3086 0.1946 0.2093 0.1249 0.0974

with reference pattern #00-043-0168, suggesting that the composite crystals retain the framework structure of zeolite-Y. It is obvious that the relative intensities of several diffraction peaks change significantly (those at around 10.2, 15.6, 18.7, 20.4°), which is likely caused by CsPb x Mn 1−x (Cl,Br) 3 embedded in the zeolites.39 There are no apparent XRD peaks originating from the CsPbxMn1−x(Cl,Br)3 perovskite, probably owing to the fact that most CsPbxMn1−x(Cl,Br)3 are located inside the pores of the zeolite. Also, the diffraction peaks of perovskite crystals with a subnano size dispersed in zeolite pores should be much weaker than that of the micronsized zeolite-Y host. Figure 2b,c gives the scanning electron microscopy (SEM) images of the original zeolite-Y and CsPb0.62Mn0.38(Cl,Br)3−Y composite. The morphology of the 24658

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

Figure 3. (a) High-angle annular dark-field scanning TEM image, and (b) elemental mapping by energy-dispersive X-ray (EDX) spectroscopy of a CsPb0.62Mn0.38(Cl,Br)3−Y composite particle (resin-embedded sections). (c) A high-resolution (HRTEM) zoom-in of a part of the crystal.

Figure 4. (a) Emission spectra of the CsPbxMn1−xCl3−Y composites and (b) CsPbxMn1−x(Cl,Br)3−Y composites. (c) The photoluminescence decay curve of the CsPb0.75Mn0.25Cl3−Y composite monitored at 408 nm with the excitation of 365 nm. (d) The photoluminescence decay curve of the CsPb0.75Mn0.25Cl3−Y composite monitored at 600 nm with an excitation of 365 nm.

Mn2+ in CsPbCl3 crystals.41 The intensity of Mn2+-emission enhances with the increased Mn2+ content, and the emission position exhibits some red-shift. As for the CsPbxMn1−x(Cl,Br)3−Y composite, the emission spectra are similar. Upon elevating the MnCl2 contents, the emission from CsPb(Cl,Br)3 crystals shows a gradual blueshift and the Mn2+emission appears. However, the band gap between the conduction band and the valence band of CsPb(Cl,Br)3 gradually narrows as the Br− concentration increases in CsPbCl3, which is not conducive to the energy transfer from exciton to Mn2+.49,58 Therefore, it can be seen that CsPbxMn1−xCl3−Y is more likely to achieve energy transfer from excitons to Mn2+, resulting in a stronger red emission.

When the halogen element in the composites is changed from chlorine to bromine completely, the band gap of the perovskite crystal is too narrow to observe the energy transfer from excitons to Mn2+ for the CsPbxMn1−xBr3−Y composite.49 The photoluminescence decay curves of the CsPb0.75Mn0.25Cl3−Y samples in Figure 4c,d also confirmed their origin. The 408 nm emission exhibits a multiexponential decay, which is consistent with the previous report of the pure perovskite QDs embedded in zeolite-Y.39 The 1/e lifetime is about 0.68 ns ascribing to the CsPbCl3−Y host radiative lifetime, and the longer lifetime of 9.53 ns is due to temporary charge-carrier trapping.60,61 600 nm emission shows a monoexponential decay with a lifetime of 0.98 ms, which is 24659

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

Figure 5. (a) Temperature-dependent emission spectra of the CsPb0.75Mn0.25Cl3−Y composite. (b) The tendency of purple and red emission intensity of CsPb0.75Mn0.25Cl3−Y as a function of temperature. (c) The tendency of purple and red emission intensity of QD films as a function of temperature. (d) The tendency of emission intensity of the QD film and the composite as a function of time immersed in water. (The time was counted when the samples were immersed in water, not including the time, we took the measurement of the photoluminescence spectra. Since it is not an in situ characterization method, the actual time of duration in water would be much longer than the recorded one.)

assigned to the Mn2+ emission with the energy transferred from excitons of perovskite QDs.41,58,62 According to our previous research, zeolite encapsulation can effectively improve the performance of CsPbX3−Y composites over the bare QDs at elevated temperatures.39 Figure 5a,b shows the temperature-dependent emission of the CsPb0.75Mn0.25Cl3−Y composite. With the increase in temperature, the intensities of the two emission peaks exhibit distinct tendencies. The CsPbCl3-related emission becomes weaker because of the temperature quenching and the peak position is almost fixed at around 410 nm. Although the Mn2+-related emission gradually enhances resulting from the intensified exciton-to-Mn2+ energy transfer. It shows a blueshift due to the changes in the ligand field strength on Mn2+ caused by thermal expansion of the perovskite lattice at elevated temperatures.41,50 Then the temperature quenching effect dominates, causing a gradual decline in both emission intensities. Compared with the bare perovskite QDs in Figure 5c, we can see that the zeolite matrix can slow down the temperature quenching significantly (specially for the purple emission of the perovskite host), proving that the encapsulation effect of the zeolites is indeed beneficial to the thermal quenching resistance of Cs(Pb,Mn)Cl3 luminescence. Temperature-

dependent emission of CsPbxMn1−x(Cl,Br)3 with similar properties is also shown in Figure S2b,c. The porous nature of the zeolite structure results in a lower thermal conductivity of the composites, which may lower the temperature of the embedded perovskites and apparently improve the temperature-dependent performance. Also, we investigated the water resistance of the composites. The CsPb0.75Mn0.25Cl3−Y composite and the QD film on a glass slide were both immersed in water and the spectra were measured immediately after varied duration times in water (Figure 5d). Obviously, the degradation rate of CsPb0.75Mn0.25Cl3 in zeolites is much slower than that of the bare perovskite QD film. After immersing for 3 min, the bare perovskite QD film shows almost no emission, whereas CsPb0.75Mn0.25Cl3−Y retains about 60% of the initial intensity. Therefore, it can be concluded that Cs(Pb,Mn)X3 is embedded inside the zeolites and the composites can achieve a much better resistance to moisture. There may be two causes for this phenomenon. On the one hand, the porous nature of the zeolite creates a barrier for the water molecules to attack the embedded perovskites. On the other hand, it may be more difficult for the perovskites in the zeolite to decompose to some extent due to the confining effect of the porous structure. 24660

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

Figure 6. (a) Output spectra of the LED, composed of a 365 nm UV chip and a CsPb0.75Mn0.25Cl3−Y orange phosphor as a function of driving current. Inset is the corresponding LED device photograph operated at 300 mA. (b) The tendency of luminous efficiency of LED as a function of operation time.

Figure 7. (a) Output spectrum of a WLED consisting of a 365 nm UV chip, a CsPb(Cl0.5,Br0.5)3−Y blue phosphor and a CsPb0.75Mn0.25Cl3−Y orange phosphor (driven current of 200 mA). Inset is the photograph of the WLEDs device. (b) The corresponding CIE coordinates of the WLED. (c) Output spectra of WLED as a function of driving current.

We know that the perovskite lead halides containing iodide ions tend to decompose even though the zeolites have been reported to slightly improve their stability over the bare CsPb(Br,I) 3 QDs. 3 9 As can be seen above, the CsPb0.75Mn0.25Cl3−Y composite exhibits a much better performance in resistance to moisture and elevated temperature in the orange-red region. Thus, it becomes a promising candidate phosphor in color-converted LED applications. Performance of Phosphor-Converted LED and WLED. To test the stability of the composites upon irradiation of light, LED was fabricated with a UV chip and CsPb0.75Mn0.25Cl3−Y as color-converted materials. Figure 6a shows the spectra of the LED device operating at a current of 50−300 mA. The CsPb0.75Mn0.25Cl3−Y composite exhibits a gradually enhancing emission as the current increases, indicating that the composite shows no decomposition toward 365 nm UV light irradiation. The inset demonstrates the photograph of the LED device working at 300 mA with the color coordinate of (0.48, 0.48) (shown in Figure S3a). Another LED consisting of the bare QDs with an analogous composition as the color-converted material was also fabricated for comparison. Current-dependent spectra are also presented in Figure S3b. Within a duration time of 10 h at 300 mA driving current, the LED with

composites shows an increasing luminous efficiency at the beginning of the operation time. This may be due to the enhanced Mn2+-related emission under elevated temperatures produced by the LED chip. Also, there is little loss of luminous efficiency after the device works for 10 h. Although the LED with the bare QDs exhibit an apparent continuous decline of up to 40%, the significantly improved performance makes the CsPbxMn1−xCl3−Y composites a promising candidate as orange-red phosphors. Finally, we assembled a WLED by coating the silicone resin mixture of CsPb(Cl0.5,Br0.5)3−Y (blue) and CsPb0.75Mn0.25Cl3−Y (orange) composites on the commercially available 365 nm LED chip. Figure 7a is the spectrum of the above mentioned WLED device operating at 200 mA. Under the excitation of an UV chip, CsPb(Cl0.5,Br0.5)3−Y produces a narrow blue emission and CsPb0.75Mn0.25Cl3−Y gives an orange broad emission, resulting in a white light with CIE coordinates of (0.34, 0.36) shown in Figure 7b. The CCT and CRI of the WLED are 5336 and 81 K, respectively. The driving current-dependent spectra (Figure 7c) show that both blue and orange emissions of composites are gradually enhanced as the current increases, and the CIE coordinates of the device exhibit little variation (Figure S4), indicating that 24661

DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces the CsPb0.75Mn0.25Cl3−Y composite is a potential orange-red component for WLED.

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CONCLUSIONS In summary, the composite of Mn2+-doped CsPbCl3 perovskite embedded in zeolite-Y was successfully prepared through a facile two-step synthesis method. The as-synthesized composites have been proved to have a much better resistance to elevated temperature and moisture compared to the bare perovskite QDs. They can be used as orange-red colorconverted materials in LEDs with superior stability against irradiation of the UV LED chip, which also behave much better than the bare orange-red QDs with iodine ions and make the composites potentially intriguing for WLED applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b08342. EDX images, temperature-dependent emission spectra, PL spectra and CIE coordinate diagrams (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (S.Y.). *E-mail: [email protected] (Q.-Y.Z.). ORCID

Shi Ye: 0000-0001-9625-8222 Qin-Yuan Zhang: 0000-0001-6544-4735 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank Dr. Xianfeng Yang for the TEM measurements, Tingting Deng and Ting Wang for the SEM measurements. This work is jointly supported by the NSFC (Grant No 51772104), the National Key R&D program (2016YFB0401702), the Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program (2016TQ03C100), and the Guangdong Natural Science Funds for Distinguished Young Scholars (2014A030306009).

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REFERENCES

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DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664

Research Article

ACS Applied Materials & Interfaces

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DOI: 10.1021/acsami.8b08342 ACS Appl. Mater. Interfaces 2018, 10, 24656−24664