Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices

Highly Stable CsPbBr3@MoS2 Nanostructures: Synthesis and Optoelectronic Properties Toward Implementation into Solar Cells

Halide perovskites (HPs) have gained significant interest in the scientific and technological sectors due to their unique optical, catalytic, and electrical characteristics. However, the HPs are prone to decomposition when exposed to air, oxygen, or heat. The instability of HP materials limits their commercialization, prompting significant efforts to address and overcome these limitations. Transition metal dichalcogenides, such as MoS2, are chemically stable and are suitable for electronic, optical, and catalytic applications. Moreover, it can be used as a protective media or shell for other nanoparticles. In this study, a novel CsPbBr3@MoS2 core-shell nanostructure (CS-NS) is successfully synthesized by enveloping CsPbBr3 within a MoS2 shell for the first time. Significant stability of CS-NSs dispersed in polar solvents for extended periods is also demonstrated. Remarkably, the hybrid CS-NS exhibits an absorption of MoS2 and quenching of the HP's photoluminescence, implying potential charge or energy transfer from HPs to MoS2. Using finite difference time domain simulations, it is found that the CS-NSs can be utilized to produce efficient solar cells. The addition of a MoS2 shell enhances the performance of CS-NS-based solar cells by 220% compared to their CsPbBr3 counterparts. The innovative CS-NS represents important progress in harnessing HPs for photovoltaic and optoelectronic applications.

Biocompatible Perovskite Nanocrystals with Enhanced Stability for White Light-Emitting Diodes

Recently emerged lead halide perovskite CsPbX3 (X = Cl, Br, and I) nanocrystals (PNCs) have attracted tremendous attention due to their excellent optical properties. However, the poor water stability, unsatisfactory luminescence efficiency, disappointing lead leakage, and toxicity have restricted their practical applications in photoelectronics and biomedical fields. Herein, a controllable encapsulated strategy is investigated to realize CsPbX3 PNCs/PVP @PMMA composites with superior luminescence properties and excellent biocompatibility. Additionally, the synthesized CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA structures exhibit green and red emissions with a maximal photoluminescence quantum yield (PLQY) of about 70.24% and 98.26%, respectively. These CsPbX3 PNCs/PVP@PMMA structures show high emission efficiency, excellent stability after water storage for 18 months, and low cytotoxicity at the PNC concentration at 500 μg mL-1. Moreover, white light-emitting diode (WLED) devices based on mixtures of CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA perovskite structures are investigated, which exhibit excellent warm-white light emissions at room temperature. A flexible manipulation method is used to fabricate the white light emitters based on these perovskite composites, providing a fantastic platform for fabricating solid-state white light sources and full-color displays.

Enhanced Photoelectric Properties of CsPbBr3 by SiO2 and TiO2 Bilayer Heterostructures

CsPbBr3/SiO2 heterostructures were synthesized by the hydrolysis reaction of a mixture of CsPbBr3 nanocrystals (NCs) and (3-aminopropyl)triethoxysilane (APTS) in air. Compared with CsPbBr3 NCs, the CsPbBr3/SiO2 heterostructures exhibit stronger photoluminescence (PL) intensity, longer lifetime of PL (∼40.5 ns), and higher PL-quantum yield (PLQY, ∼86%). The carrier dynamics of CsPbBr3/SiO2 was detected by the transient absorption (TA) spectrum. The experimental results show that SiO2 passivates the surface traps of CsPbBr3 NCs and enhances the PL intensity. However, photoelectrochemical impedance spectra (PEIS) demonstrate that the impedance of CsPbBr3/SiO2 is higher than that of CsPbBr3 NCs, which reduces carrier transport and extraction. Because the application of CsPbBr3/SiO2 in optoelectronics is limited, CsPbBr3/SiO2/TiO2 heterostructures were synthesized by the further reaction of tetrabutyl titanate (TBT). The TiO2 coating can reduce the impedance of the CsPbBr3/SiO2. Importantly, ∼68% of the PL intensity of CsPbBr3/SiO2 is retained. Compared with CsPbBr3/SiO2 and CsPbBr3 NCs, the CsPbBr3/SiO2/TiO2 demonstrates faster carrier transport (κct = 2.4 × 109 s-1) and higher photocurrent density (J = 76 nA cm-2). In addition, CsPbBr3/SiO2/TiO2 shows good stability under (ultraviolet) UV irradiation, along with water stability and thermal stability. Therefore, the double protection approach can enhance the stability of CsPbBr3 NCs and tune the optoelectronic properties of CsPbBr3 NCs.

Highly Thermally Sensitive Cascaded Wannier-Mott Exciton Ionization/Carrier Localization in Manganese-Doped Perovskite Nanocrystals

Transition-metal doping in perovskite nanocrystals strongly alters the photophysical properties of these nanocrystals. However, the details of the underlying thermal and optical processes within such an intriguing symmetry-breaking nanosystem are far from clear. Herein, we study the sensitively temperature-dependent and highly competent delocalized exciton and transition-metal ion-captured carrier recombination processes in manganese-doped CsPbBr_0.6Cl_2.4 nanocrystals. The combined experimental and theoretical studies reveal that both the exciton ionization and capture of the band-edge carriers by the manganese ions play the dominant roles in determining the proportion of the manganese ions-dominated recombination process. A density functional theory calculation of the temporal fluctuation of the manganese ions-accommodated localized orbitals further confirms that the thermally enhanced nonadiabatic electron-phonon coupling promotes the probability of the carrier localization. These findings reveal the respective crucial roles of the exciton ionization and carrier capture in the localized recombination process in the transition-metal-doped semiconductor nanocrystals.

Heavy Mn-doped CsPbBr3nanocrystals synthesized by high energy ball milling with high stability

CsPbX₃(X = Cl, Br, I) semiconductor nanocrystals (NCs) have excellent optical and photoelectric properties, and are potential core materials for various photoelectric devices. However, the toxicity of Pb and instability have been the key limitations to application of NCs. Herein, using MnBr₂and MnBr₂·4H₂O as manganese sources, heavy Mn-doped CsPbBr₃(Mn:CsPbBr₃) NCs are synthesized by high-energy ball grinding, which avoids high temperature, a large number of polar solvents and atmosphere protection required in traditional liquid phase methods. However, when MnBr₂·4H₂O is used as the raw material, infinite solid solution doping can be achieved, and the synthesized Mn:CsPbBr₃NCs show smaller particle size, stronger PL intensity and stability. The reason is that presence of crystal water plays a similar role to wet milling in the ball milling process, and can promote the passivation effect of oleylamine (OAm) on nanocrystal defects and the connection between them. In addition, a simple, easy-operating and beneficial to commercial production method for the preparation of Mn:CsPbBr₃NCs/EVA flexible films is proposed, which can effectively improve the stability of Mn:CsPbBr₃NCs. This study is expected to provide an effective way for the synthesis and stability improvement of CsPbX₃NCs doped with different ions.

Enhanced photoluminescence stability and internal defect evolution of the all-inorganic lead-free CsEuCl3 perovskite nanocrystals

Perovskite materials are prominent candidates for many high-performance optoelectronic devices. The rare-earth lead-free CsEuCl₃ perovskite nanocrystals are extremely unstable, which makes it very difficult to study their physicochemical properties and applications. Herein, we improved the stability of rare-earth based CsEuCl₃ nanocrystals by employing a silica-coating for the first time. Simultaneously, the naturally formed "hollow" regions with an obviously blue-shifted PL emission were first observed inside the CsEuCl₃ nanocrystals during the period of storage. Density functional theory (DFT) calculations showed that the formed "hollow" regions are due to the internal defect evolution in the perovskite lattice, which is also responsible for the increase of the bandgap and the blue-shift of emission. Additionally, the rapid decline of luminescence is probably due to the nanocrystals' final cracking with the expansion of the "hollow" regions. This work helps to understand the relationship between defects and luminescence properties, and provides guidance for the design of more stable lead-free perovskite nanocrystals.

Systematic Microwave-Assisted Postsynthesis of Mn-Doped Cesium Lead Halide Perovskites with Improved Color-Tunable Luminescence and Stability

The metal doping at the Pb²⁺ position provides improved luminescence performance for the cesium lead halide perovskites, and their fabrication methods assisted by microwave have attracted considerable attention due to the advantages of fast heating and low energy consumption. However, the postsynthetic doping strategy of the metal-doped perovskites driven by microwave heating still lacks systematic research. In this study, the assembly of CsPbBr₃/CsPb₂Br₅ with a strong fluorescence peak at 523 nm is used as the CsPbBr₃ precursor, and through the optimization of the postsynthetic conditions such as reaction temperatures, Mn²⁺/Pb²⁺ feeding ratios, and Mn²⁺ sources, the optimum Mn²⁺-doped product (CsPb(Cl/Br)₃:Mn) is achieved. The exciton fluorescence peak of CsPb(Cl/Br)₃:Mn is blueshifted to 437 nm, and an obvious fluorescence peak attributing to the doped Mn²⁺ ions at 597 nm is obtained. Both the CsPbBr₃ precursor and CsPb(Cl/Br)₃:Mn have high PLQY and stability because there are CsPb₂Br₅ microcubic crystals to well disperse and embed the CsPbBr₃ nanocrystals (NCs) in the precursor, and after Mn²⁺-doping, this structure is maintained to form CsPb(Cl/Br)₃:Mn NCs on the surface of their microcrystals. The exploration of preparation parameters in the microwave-assisted method provides insights into the enhanced color-tunable luminescence of the metal-doped perovskite materials.

Ligand-mediated CsPbBrxI3-x/SiO2quantum dots for red, stable and low-threshold amplify spontaneous emission

The red-emitting perovskite material has received widespread attention as a long-wavelength optical gain media. But the easy phase change in the air limits its practical application. Herein, red CsPbBr_xI_3-x/SiO₂quantum dots (QDs) are prepared by a ligand-mediated hot injection method in which 3-aminopropyl-triethoxysilane (APTES) is used instead of the usual oleylamine (OAm) ligand. Through the hydrolysis of amino groups, a thin silicon layer is formed on the QD surface, improving the stability and without causing the aggregation of QDs. We find that the ratio of I/Br and the size of QDs can be tuned by adjusting the APTES amount. Moreover, this ligand-mediated synthesis effectively passivates the surface defects, so the photoluminescence quantum yield is remarkably improved, and the carrier lifetime is prolonged. The amplified spontaneous emission is achieved under 532 nm nanosecond laser excitation. Compared with the original CsPbBrI₂-OAm QD films, the threshold of CsPbBr_xI_3-x/SiO₂QD films is reduced from 403.5 to 98.7μJ cm^-2, and the radiation stability is significantly enhanced. Therefore, this material shows great potential in the random laser field.

White light emission from lead-free mixed-cation doped Cs2SnCl6 nanocrystals

We have designed a synthesis procedure to obtain Cs₂SnCl₆ nanocrystals (NCs) doped with metal ion(s) to emit visible light. Cs₂SnCl₆ NCs doped with Bi³⁺, Te⁴⁺ and Sb³⁺ ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi³⁺ and Te⁴⁺ ions were synthesized in a single run. Combination of both dopant ions together gives rise to the white emission. The photoluminescence quantum yields of the blue, yellow and white emissions are up to 26.5, 28, and 16.6%, respectively under excitation at 350, 390, and 370 nm. Pure white-light emission with CIE chromaticity coordinates of (0.32, 0.33) and (0.32, 0.32) at 340 and 370 nm excitation wavelength, respectively, was obtained. The as-prepared NCs were found to demonstrate a long-time stability, resistance to humidity, and an ability to be well-dispersed in polar solvents without property degradation due to their hydrophilicity, which could be of significant interest for wide application purposes.

Phase-sensitive radioluminescent and photoluminescent features in Tm3+-doped yttrium tantalates for cyan and white light generation

Radioluminescence and visible photoluminescent tunability features from a single Tm3+-doped yttrium tantalate phosphor prepared by a soft sol–gel method designed to afford cubic Y3TaO7 and monoclinic M’-YTaO4 crystalline phases are...

Room-Temperature Synthesis of Air-Stable Near-Infrared Emission in FAPbI3 Nanoparticles Embedded in Silica

Hybrid organic-inorganic and all-inorganic metal halide perovskite nanoparticles (PNPs) have shown their excellent characteristics for optoelectronic applications. We report an atmospheric process to embed formamidinium CH(NH2)2PbI3 (FAPbI3) PNPs in silica protective layer at room temperature (approximately 26 °C) employing (3-aminopropyl) triethoxysilane (APTES). The resulting perovskite nanocomposite (PNCs) achieved a high photoluminescence (PL) quantum yield of 58.0% and good stability under atmospheric moisture conditions. Moreover, the PNCs showed high PL intensity over 1 month of storage (approximately 26 °C) and more than 380 min of PNCs solutions in DI water. The studied near-infrared (NIR) light-emitting diode (LED) combined a NIR-emitting PNCs coating and a blue InGaN-based chip that exhibited a 788 nm electroluminescence spectrum of NIR-LEDs under 2.6 V. This may be a powerful tool to track of muscle and disabled patients in the detection of a blood vessel.

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes

The tunable dual-color emitting Mn²⁺ doped CsPbCl_3-xBr_x nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr₂ treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn²⁺ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn²⁺ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn²⁺ doped CsPbCl_1.5Br_1.5 NCs are obtained. The enhancement mechanism of Mn²⁺ PL QY was attributed to improved energy transfer from exciton to Mn²⁺ d-d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn²⁺ doped CsPbCl_3-xBr_x@SiO₂ and green emissive CsPbBr₃@SiO₂ NCs with violet GaN chips.

Novel cryogenic dual-emission mechanism of lead-free double perovskite Cs2AgInCl6 and using SiO2 to enhance their photoluminescence and photostability

Lead halide perovskite have attracted world-wide attention regarding their serious hazards on ecological environment and human health. To improve both the emission intensity and stability of Cs₂AgInCl₆, this study explores using SiO₂ to structurally adjust Cs₂AgInCl₆. Note that including SiO₂ changed the growth style and crystal morphology of Cs₂AgInCl₆ from an octahedron to a truncated octahedron. After structural adjustment, the unit cells scattered, and the absorption limit broke. Moreover, SiO₂ was demonstrated to passivate the material's surface to form an anti-oxidation protective layer. Consequently, the photoluminescence emission intensity increased by 181.5% and the stability of Cs₂AgInCl₆ improved by 83.11%. This work provides a methodology and reference for future improvements to the luminescence of Cs₂AgInCl₆. Furthermore, a novel double-emission phenomenon (λ_ex = 365 nm: λ_em ≈ 580 nm; λ_ex = 325 nm: λ_em ≈ 505 nm) of Cs₂AgInCl₆ at cryogenic temperatures (20 K) was discovered; this phenomenon explains the shoulder emission problem of 400-450 nm at room temperature and clarifies the luminescence mechanism of Cs₂AgInCl₆.

Solid-state thiolate-stabilized copper nanoclusters with ultrahigh photoluminescence quantum yield for white light-emitting devices

As a new emerging candidate for solid-state phosphors, copper nanoclusters (CuNCs) have gained tremendous interest in the field of white light-emitting devices (WLEDs). However, their further applications are impeded by the low photoluminescence quantum yield (PLQY) and poor emission color tunability of CuNCs. This work demonstrates the synthesis of cyan and orange emitting CuNCs, and their combination as color conversion phosphors in WLEDs. The cyan and orange emitting CuNCs were prepared employing 2-mercapto-1-methylimidazole (MMI) and N-acetyl-l-cysteine (NAC), respectively, as stabilizing-cum-reducing agents. The dispersions of MMI-CuNCs and NAC-CuNCs are weakly emissive. However, after processing into powders, they both possess ultrahigh PLQYs (45.2% for MMI-CuNCs, and 64.6% for NAC-CuNCs) owing to the effect of aggregation-induced emission (AIE). All-CuNC based WLEDs are then designed and developed using powdered MMI-CuNC and NAC-CuNC samples on commercially available 365 nm GaN LED chips. They display acceptable white light characteristics with a Commission Internationale de l'Eclairage coordinate value and color rendering index of (0.26, 0.30) and 83, respectively. We believe that these cost-effective and eco-friendly CuNCs with interesting AIE properties will vigorously promote the development of high-quality WLEDs for commercial applications.

Advances in the Stability of Halide Perovskite Nanocrystals

Colloidal halide perovskite nanocrystals are promising candidates for next-generation optoelectronics because of their facile synthesis and their outstanding and size-tunable properties. However, these materials suffer from rapid degradation, similarly to their bulk perovskite counterparts. Here, we survey the most recent strategies to boost perovskite nanocrystals stability, with a special focus on the intrinsic chemical- and compositional-factors at synthetic and post-synthetic stage. Finally, we review the most promising approaches to address the environmental extrinsic stability of perovskite nanocrystals (PNCs). Our final goal is to outline the most promising research directions to enhance PNCs' lifetime, bringing them a step closer to their commercialization.

Orange to Red, Emission-Tunable Mn-Doped Two-Dimensional Perovskites with High Luminescence and Stability

Lead halide perovskites are emerging as promising candidates for high-efficiency light-emitting diode (LED) applications because of their tunable band gaps and high quantum yield (QY). However, it remains a challenge to obtain stable red emitting materials with high QY. Herein, we report a facile and convenient hot-injection strategy to synthesize Mn-doped two-dimensional (2D) perovskite nanosheets. The emission peak can be tuned from 597 to 658 nm by manipulating the crystal field strength. In particular, a QY as high as 97% for 2D perovskite is achieved. The as-prepared perovskite also possesses excellent stability, whose emission property can be maintained for almost one year. A monochrome LED is further fabricated by employing the as-prepared perovskite as phosphor, which also shows high long-term stability. We believe that these highly efficient and stable perovskites will open up new opportunities in LED applications.

Ultrastable Carbon Quantum Dots-Doped MAPbBr3 Perovskite with Silica Encapsulation

Having suffered from intrinsic structural lability, perovskite quantum dots (PQDs) are extremely unstable under high-temperature and moisture conditions, which have greatly limited their applications. In this work, we propose a novel method to synthesize ultrastable carbon quantum dots (CQDs)-doped methylamine (MA) lead bromide PQDs with SiO₂ encapsulation (CQDs-MAPbBr₃@SiO₂). The kernel CQDs-MAPbBr₃ is formed by the interaction of carboxyl-rich CQDs with MAPbBr₃ via H-bond, which greatly improves the thermal stability of CQDs-MAPbBr₃. Furthermore, highly compact SiO₂ encapsulates the proposed CQDs-MAPbBr₃ via a facile in situ growth strategy, which effectively enhances the water resistance and air stability of CQDs-MAPbBr₃@SiO₂. As a result, the proposed nanomaterial shows extremely high water stability in aqueous solution for over 9 months and ideal thermal stability with strong fluorescence (FL) emission after 150 °C annealing. Based on the superior stability and ultrahigh FL efficiency of this proposed nanomaterial, a primary sensing method for ion (Ag⁺ and Zn²⁺) FL detection has been developed and the mechanism of PQDs-based ion determination has also been discussed, thus exhibiting the potential applications of CQDs-MAPbBr₃@SiO₂ in the area of FL assay and environment monitoring.

White light-emitting diodes based on carbon dots and Mn-doped CsPbMnCl3 nanocrystals

CsPbX₃ perovskite nanocrystals (NCs) are becoming a promising material for optoelectronic devices that possess an optically tunable bandgap, and bright photoluminescence. However, the toxic Pb is not environmentally friendly and the quantum yield (QY) of blue emitting NCs is relatively low. In addition, the red emitting perovskite containing iodine is not stable under light illumination. In this paper, high QY, blue emitting, non-toxic fluorescent nanomaterial carbon dots and orange-emitting CsPb_0.81Mn_0.19Cl₃ NCs with partial Pb replacement are combined to fabricate white light-emitting diodes (WLEDs). A WLED with color coordinates of (0.337, 0.324) and a correlated color temperature of 4804 K is fabricated. Compared to red emitting perovskite containing iodine, the CsPb_0.81Mn_0.19Cl₃ NCs are stable no matter whether they are stored in the air or exposed under ultraviolet light. Therefore, the as-fabricated WLED shows good color stability against increasing currents and long-term working stability.

Ultrathin, Core-Shell Structured SiO2 Coated Mn2+ -Doped Perovskite Quantum Dots for Bright White Light-Emitting Diodes

All-inorganic semiconductor perovskite quantum dots (QDs) with outstanding optoelectronic properties have already been extensively investigated and implemented in various applications. However, great challenges exist for the fabrication of nanodevices including toxicity, fast anion-exchange reactions, and unsatisfactory stability. Here, the ultrathin, core-shell structured SiO₂ coated Mn²⁺ doped CsPbX₃ (X = Br, Cl) QDs are prepared via one facile reverse microemulsion method at room temperature. By incorporation of a multibranched capping ligand of trioctylphosphine oxide, it is found that the breakage of the CsPbMnX₃ core QDs contributed from the hydrolysis of silane could be effectively blocked. The thickness of silica shell can be well-controlled within 2 nm, which gives the CsPbMnX₃ @SiO₂ QDs a high quantum yield of 50.5% and improves thermostability and water resistance. Moreover, the mixture of CsPbBr₃ QDs with green emission and CsPbMnX₃ @SiO₂ QDs with yellow emission presents no ion exchange effect and provides white light emission. As a result, a white light-emitting diode (LED) is successfully prepared by the combination of a blue on-chip LED device and the above perovskite mixture. The as-prepared white LED displays a high luminous efficiency of 68.4 lm W^-1 and a high color-rendering index of Ra = 91, demonstrating their broad future applications in solid-state lighting fields.

CsPbBr3 Quantum Dot Films with High Luminescence Efficiency and Irradiation Stability for Radioluminescent Nuclear Battery Application

Highly luminescent CsPbBr₃ perovskite quantum dots (QDs) are very attractive for applications in power-generating devices. The CsPbBr₃ QD solution and its corresponding solid films were satisfactorily prepared. The obtained QDs were characterized by various techniques such as transmission electron microscopy, X-ray diffraction, ultraviolet-visible spectrophotometry, and photoluminescence and radioluminescence spectroscopy. The performance of the CsPbBr₃ QD films as an energy conversion material in radioluminescent nuclear batteries was analyzed and discussed. The output performance of different nuclear batteries based on CsPbBr₃ QD films was compared and the feasibility and advantages of using them as radioluminescent layers were investigated. On this basis, a long-term equivalent service behavior study was conducted to evaluate the irradiation stability of the CsPbBr₃ radioluminescent layer and predict the service life of this type of nuclear battery. The distribution state and penetration depth of hydrogen ions in the films were analyzed and evaluated using physics simulation software. Optical and electrical characteristics confirmed that this perovskite material could offer an efficient, stable, and scalable solution for energy conversion and photoelectric detection in the future.

Room temperature synthesis of Mn-doped Cs3Pb6.48Cl16 perovskite nanocrystals with pure dopant emission and temperature-dependent photoluminescence

We report Mn-doped Cs₃Pb_6.48Cl₁₆ nanocrystals with pure dopant emission synthesized at room temperature.