CsPbX3 Quantum Dots Research Articles

Investigation of spectral-luminescent properties of cesium CsPb(BrCl)3 quantum dots in fluorophosphate glasses

Within the framework of the scientific project “Investigation of spectral-luminescent properties of CsPb(BrCl)3 quantum dots in fluorophosphate glasses” CsPbX3 (X = Br, Cl) quantum dots were synthesized and investigated. The absorption spectra were studied using a Perkin Elmer lambda 650 double beam spectrophotometer. A Perkin Elmer LS50B spectrofluorimeter was used to obtain luminescence spectra. The temperature dependences were studied by means of an original setup, including a spectrofluorimeter, a multimode optical fiber, a cryostat and a temperature stand. The exciting light from the spectrofluorimeter lamp was focused on the input channel of the optical fiber. After leaving the channel, the radiation was collected by a lens in the focus of which was a sample fixed in a thermostat. The luminescence of the sample was collected in the opposite direction with the output to the receiver of the spectrofluorimeter, which is connected to the computer. The thermostat, in turn, was connected to a cryogenic set-top box with variable temperature, which allows adjusting the temperature in the range from 74 to 472 K. It is shown that an increase in the heat treatment time leads to an increase in quantum dots and, accordingly, to a decrease in the band gap due to the quantum confinement effect. When replacing bromine in CsPbBr3 with chlorine, mixed CsPb(BrCl)3 nanocrystals were obtained which leads to a shift of the absorption and luminescence bands to the short-wavelength region. Thus, by choosing different ligands for CsPbX3 (X = Br, Cl), changing their ratio and heat treatment conditions, it is possible to adjust the wavelength of luminescence in a wide area of the visible range. The study of the dependence of the band gap width on temperature clearly showed the presence of phase transformations of the crystal structure. The sequence of phase transitions for various chemical compositions was determined, namely, the contribution of chlorine to the change in dependence in the range from 180 to 400 K. It is assumed that the main causes of luminescence quenching above 300 K are phase transitions. As a result, it is proved that fluorophosphate glass is a chemically stable medium for protecting quantum dots from external influences. The possibility of creating stable phosphors, new laser media and luminescent coatings of both white light and in the entire visible range has been obtained

Tri-chromatic luminescence of CsPb(Cl/Br)3 quantum dots-Tb3+-Mn2+ co-doped single component glasses for white LED application

Recently, CsPbX3 quantum dots (QDs) doping Mn2+ have been researched for application in white LED, but the main problem is low color render index (Ra) due to deficient green light. We have fabricated novel CsPb(Cl/Br)3 QDs-Tb3+-Mn2+ trichromatic glasses for white LED application. The interaction mechanism has been investigated by using QDs, Mn, Tb, QDs-Mn, QDs-Tb, Mn–Tb and QDs-Mn-Tb samples. Wide tri-chromatic photoluminescence (PL) spectra have been obtained by optimizing PL peak of the QDs, concentrations of QDs, Tb3+ and Mn2+, and heat treatment conditions. The PL peak of QDs is 442 nm. The molar concentrations are 2%, 0.36–0.60% and 3% for CsPb(Cl/Br)3 QDs, Tb3+ and Mn2+ respectively. The heat treatment conditions are 420 for 3 h and 450–470 °C for another 3 h. Color coordinates are adjusted in the warm white light range. Correlated color temperature (CCT) is adjustable in the range of 3136–4474 K. Ra is in the suitable range of 66–86. Based on temperature dependent PL spectra in the range of 25–80 °C, the color coordinates, CCT and Ra are calculated and they are still in the warm light range and suitable for white LED application. The trichromatic glasses excited at 378 nm have potential application in white LED lighting.

All-inorganic halide perovskite (CsPbX3, X=Cl, Br, I) quantum dots synthesized via fast anion hot injection by using trimethylhalosilanes

All-inorganic metal halides perovskites, such as CsPbX3 quantum dots (QDs), are high-performance photoelectric materials; they have attracted considerable attention for applications such as LEDs and laser and solar cells. Herein, we report an anion hot injection (HI) method to prepare CsPbX3 (X = Cl, Br, I, Cl/Br, and Br/I) QDs using trimethylhalosilane (TMXS) as a halogen ion donor. By adjusting the ratio of different TMXSs (trimethylchlorosilane, trimethylbromosilane, and trimethyliodosilane), the synthesized samples can achieve tunable emission in the range of 416–710 nm, narrow emission line widths of 13–33 nm, and luminescence lifetimes of 32–223 ns. These QDs also have better stability in external environment compared with those obtained using traditional HI method.

Preparation and photoluminescence of Cs4PbBr6 perovskite quantum dot embedded in borophosphate glass

Zero dimensional perovskite CsPbX3 and Cs4PbX6 (XI, Br and Cl) quantum dots are becoming a potential object for optoelectronic device applications. However, the instability of perovskite CsPbX3 and Cs4PbX6 quantum dots in air hinders their wide practical application. The perovskite quantum dots embedded in glass matrix can improve their stability, and the perovskite CsPbX3 quantum dots embedded in the glass were extensively reported. In this work, a novel borophosphate glass containing Cs4PbBr6 quantum dots was prepared. The morphological characteristics of Cs4PbBr6 quantum dots in the glass were analyzed by transmission electron microscopy. The luminescence characteristics of Cs4PbBr6 quantum dots are exhibiting the green luminescence. The luminescence intensity of Cs4PbBr6 quantum dots embedded in glass can still maintain about 94% after immersion in water for 240 h, which overcome the instability of perovskite Cs4PbBr6 quantum dots affected easily by environment. The results demonstrated that the boron phosphorus fluorine antimony glass containing Cs4PbBr6 quantum dots may have a potential application prospect in solid-state lighting and display area.

4‐Bromo‐Butyric Acid‐Assisted In Situ Passivation Strategy for Superstable All‐Inorganic Halide Perovskite CsPbX3 Quantum Dots in Polar Media

AbstractA crucial challenge is to develop an in situ passivation treatment strategy for CsPbX3 (CPX, X=Cl, Br, and I) quantum dots (QDs) and simultaneously retain their luminous efficiency and wavelength. Here, a facile method to significantly improve the stability of the CPX QDs via in situ crystallization with the synergistic effect of 4‐bromo‐butyric acid (BBA) and oleylamine (OLA) in polar solvents including aqueous solution and a possible fundamental mechanism are proposed. Monodispersed CsPbBr3 (CPB) QDs obtained in water show high photoluminescence quantum yields (PLQYs) of 86.4 % and their PL features of CPB QDs have no significant change after being dispersed in aqueous solution for 96 h, which implies the structure of CPB QDs is unchanged. The results provide a viable design strategy to synthesize all‐inorganic perovskite CPX QDs with strong stability against the attack of polar solvents and shed more light on their surface chemistry.

4-Bromo-Butyric Acid-Assisted In Situ Passivation Strategy for Superstable All-Inorganic Halide Perovskite CsPbX3 Quantum Dots in Polar Media.

A crucial challenge is to develop an in situ passivation treatment strategy for CsPbX3 (CPX, X=Cl, Br, and I) quantum dots (QDs) and simultaneously retain their luminous efficiency and wavelength. Here, a facile method to significantly improve the stability of the CPX QDs via in situ crystallization with the synergistic effect of 4-bromo-butyric acid (BBA) and oleylamine (OLA) in polar solvents including aqueous solution and a possible fundamental mechanism are proposed. Monodispersed CsPbBr3 (CPB) QDs obtained in water show high photoluminescence quantum yields (PLQYs) of 86.4 % and their PL features of CPB QDs have no significant change after being dispersed in aqueous solution for 96 h, which implies the structure of CPB QDs is unchanged. The results provide a viable design strategy to synthesize all-inorganic perovskite CPX QDs with strong stability against the attack of polar solvents and shed more light on their surface chemistry.

Ambipolar Photoresponse of CsPbX3-ZnO (X = Cl, Br, and I) Heterojunctions

All-inorganic perovskite CsPbX3 (X = Cl, Br, and I) quantum dots (QDs) are emerging as attractive materials for photodetectors due to their prominent positive photoresponse. In this work, ambipolar photodetectors were constructed based on heterojunctions of CsPbX3 QDs and ZnO nanocrystals (NCs). The transition between the positive photoconductivity (PPC) and negative photoconductivity (NPC) was successfully controlled not only by the drain-source voltage (VDS) but also by the excitation wavelength and CsPbX3 crystal size. A high responsivity (R), on–off ratio (η), and detectivity (D*) were achieved for NPC (R = 1046 mA/W, η = 281, and D* = 1.65 × 1011 Jones), with PPC (R = 146 mA/W, η = 64, and D* = 1.54 × 1011 Jones) simultaneously revealed in the same device. A general mechanism combining the type-II heterojunction, the component and size-related band structure, and most critically the in-band trap states of the perovskites was established for understanding the unique ambipolar property. It exhibits application potential in developing functional photodetectors, memristors, and optical logic devices.

In Situ Growth Mechanism of CsPbX3 (X = Cl, Br, and I) Quantum Dots in an Amorphous Oxide Matrix

In Situ Growth Mechanism of CsPbX₃ (X = Cl, Br, and I) Quantum Dots in an Amorphous Oxide Matrix

Multi-parameter temperature prediction based on optical fiber filled with CsPbX3 QDs

To expand the range of application of quantum dots in the field of temperature sensing, this paper proposed three kinds of temperature sensors based on CsPbX3 (X = Br, Br/I, and I) quantum dots filling into hollow-core fibers. Based on the photoluminescence properties of quantum dots, quantum dots were prepared by the hydrothermal method and later filled in hollow-core optical fibers to fabricate three kinds of temperature sensors. In this paper, the temperature dependence of photoluminescence of quantum dot sensors has been studied. In detail, temperature variation characteristics of integrated photoluminescence, full width at half maximum, and central wavelength of the photoluminescence spectrum have been investigated. It is found that the integrated photoluminescence, full width at half maximum, and central wavelength all fluctuate regularly with temperature. In this paper, the support vector regression method is employed to determine the mathematical relation between integrated photoluminescence, full width at half maximum, central wavelength, and temperature. Later, the three parameters are used to achieve fast and accurate temperature measurement. The experimental results show that in the range of 30–100⁡°C, the precision of the optical fiber temperature sensors based on quantum dots is below 2⁡°C.

Photon upconversion of all-inorganic CsPbX3 quantum dots based on fluorescence resonance energy transfer in hetero-structured perovskite/upconversion nanocomposites

Photo upconversion that converts low-energy light into high-energy photons holds great promise for boosting the energy conversion efficiencies particularly for photovoltaic devices based on all-inorganic CsPbX3 (X = Cl, Br, and I) perovskite quantum dots. However, the realization of nonlinear upconversion luminescence (UCL) from these all-inorganic CsPbX3 perovskites has been met with very limited success until now. Herein, we propose a rational perovskite/upconversion hetero-structured design strategy to achieve excitonic UCL of all-inorganic CsPbX3 perovskites based on fluorescence resonance energy transfer (FRET), where all-inorganic CsPbX3 perovskites and upconverting CaF2:Ln (Ln = Yb3+/Er3+, Yb3+/Ho3+, and Yb3+/Tm3+) nanocrystals are closely integrated with each other as a whole by using a modified two-step epitaxial growth approach, forming the unique upconverting CsPbX3/CaF2:Ln hetero-structured nanocomposites (HSNCs). Benefitting from the extremely high FRET efficiency of ∼99.7%, excitonic UCL from CsPbX3 perovskites can be realized upon low-power density 980-nm diode laser irradiation. More importantly, all the HSNCs are found to outperform their pure CsPbX3 counterparts in terms of air-stability, thermal-stability, and excitonic downconversion luminescence intensity, clearly demonstrating the overwhelming advantages of upconverting HSNCs we prepared over the pure CsPbX3 perovskites for high-performance optoelectronic and photovoltaic applications.

Ionic liquid assisted pure blue emission CsPbBr3 quantum dots with improved optical properties and alkyl chain regulated stability

Stability issue of blue emitting CsPbX3 quantum dots (QDs) remains a great challenge for their application in optoelectronic devices. In this work, hydrophobic ionic liquids (ILs) 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (NTf2) were used to obtain blue emission CsPbBr3 QDs with high color purity featured with a 16 nm full width at half-maximum (FWHM). Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results elucidated ILs formed effective passivation on QDs through stronger interaction with surface Pb2+ compared to OA/OAm. This passivation effect led to the enhancement of photoluminescence quantum yields (PLQYs) from 33% for the pristine sample to 51% for QDs modified by ILs. And the stability of the modified QDs was enhanced by keeping the blue emitting even after 32 h UV irradiation. More interestingly, there is an alkyl chain effect existed that QDs with longer alkyl chain ILs exhibit better stability than the ones with shorter alkyl chains. It may relate to the higher hydrophobicity originated from long alkyl chain. Resultantly, Warm white light emitting diode (WLED) based on the IL-contained QDs was fabricated which qualified with a Commission Internationale de L'Eclairage (CIE) color coordinates of (0.33,0.35), Correlated color temperature (CCT) of 5416 K and maximum luminance of 9062.9 cd/m2. The demonstrated ILs passivation strategy might be an effective method for preparing blue emitting perovskite QDs with high PLQYs and stability.

One-step precipitated all-inorganic perovskite QDs from amorphous media for backlighting display and reproducible laser-driven white lighting

Embedded within an inorganic amorphous media, all-inorganic perovskite CsPbX3 (X = Br, I) quantum dots (QDs) overcome the limitation of poor stability for practical application, which has attracted widespread attention. However, the employed thermal treatment strategies for the melting procedure to obtain the amorphous matrix are time- and energy-consuming. Here, we propose an efficient and cost-saving approach for mass production of CsPbBr3 QDs@glass one-step, which maintains the high photoluminescence quantum yield (PLQY 47 %) and narrow full width at half maximum (FWHM 24 nm) of CsPbBr3 QDs. Furthermore, a red shift from 523 to 645 nm of the as-prepared perovskite is achieved by adjusting the halogen composition of the amorphous host from Br to Br/I. Herein, the well-addressed photo- and moisture-stability of the green CsPbBr3 and red CsPbBr1.2I1.8 QDs@glass perovskites endow a 118 % National Television Standards Committee (NTSC) and 88 % Rec. 2020 standards color gamut, combined with a commercial blue GaN chip, for state-of-the-art backlighting display. Moreover, it is found that the performance degradation of the laser-driven white lighting device, causing by the damages of high-power laser irradiation, can be fully recovered after a facile thermal treatment process. We believe that the synthesis strategy opens up a new avenue for the large scale synthesis of high quality perovskite QDs with low cost.

Novel and stable CsPbX3-TS-1 (X = Br, I) nanocomposites for light-emitting diodes

CsPbX3 (X = Br, I) quantum dots (QDs) have gradually become the star materials in light-emitting diodes (LED), but its stability has a big impact on development. Here, a variety of novel CsPbX3-TS-1 nanocomposites have been fabricated and the luminescence wavelength can be tunable by varying the halide nanocomposites (Br, I). What's particularly nice is that the original photoluminescence quantum yield (PLQY) of CsPbBr1l2 QDs approaches 82% and it still has close to 74% after being combined with TS-1. Besides, the nanocomposites enhance stability resisting moisture, thermal stressing and light. In addition, a 460 nm InGaN blue chip, YAG:Ce3+ and CsPbBr1I2-TS-1 were equipped with white light emitting diodes (WLEDs), with a luminous effect of 95 lm/W, a color rendering index of 80, and a color temperature of 5144 K. Meanwhile, wide color gamut (116% of the National Television Standards Committee, 86.3% of the ITU-R Recommendation BT. 2020) and great chromaticity coordinate (0.3425, 0.3408) are realized. This is a very important step to open up the awkward situation of the practical application of perovskite QDs materials in LED.

CsPbX3 -ITO (X = Cl, Br, I) Nano-Heterojunctions: Voltage Tuned Positive to Negative Photoresponse.

All-Inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted tremendous attention in the past few years for their appealing performance in optoelectronic applications. Major properties of CsPbX3 QDs include the positive photoconductivity (PPC) and the defect tolerance of the in-band trap states. Here it is reported that when hybridizing CsPbX3 QDs with indium tin oxide (ITO) nanocrystals to form CsPbX3 -ITO nano-heterojunctions (NHJs), a voltage tuned photoresponse-from PPC to negative photoconductivity (NPC) transform-is achieved in lateral drain-source structured ITO/CsPbX3 -ITO-NHJs/ITO devices. A model combining exciton, charge separation, transport, and most critical the voltage driven electron filling of the in-band trap states with drain-source voltage (VDS ) above a threshold, is proposed to understand this unusual PPC-NPC transform mechanism, which is different from that of any known nanomaterial system. This finding exhibits potentials for developing devices such as photodetectors, optoelectronic switches, and memories.

Robust CsPbBr3 and CdSe / Dy3++CdSe quantum dot doped glass nanocomposite hybrid coupling as color converter for solid-state lighting applications

CsPbX3 (X = Br-, Cl-, I-) and IIB-VIA group quantum dots (QDs) exhibit great potential for diverse opto-electronic applications due to their outstanding photoluminescence features. However, poor long-term stability limits their integration into practical applications. Although various surface modification and encapsulation methods have been proposed to increase their durability, desired stability values along with favorable emission properties could not be achieved yet. In this work, controlled crystallization of CsPbBr3 and CdSe QDs are realized separately in a specially tailored silicate glass matrix to obtain quantum dot doped glass nanocomposite (GNC) layers showing typical bright green emission and broadband emission that covers red end of the visible spectrum, respectively. Two alternative white LED devices are constructed as a proof-of-concept by coupling CsPbBr3 doped layer with CdSe and Dy3++CdSe doped layers on top of a blue LED chip to demonstrate excellent color conversion performance and challenging color rendering index values up to 85. CsPbBr3 doped GNC layer exhibits photoluminescence quantum yield (PLQY) up to 40.44%, while PLQY of CdSe doped layer is enhanced up to 18.68% via incorporation of Dy3+ ions. PL properties of GNCs are reversible up to 275 °C and stable after 60 days of immersion in water or under 442 nm laser irradiation (5 W/cm2) up to 30 min. Promising thermal, chemical, and photo stability properties reveal that hybrid coupling of GNCs exhibit high potential to be used as color convertors in solid-state lighting applications.

Synergistic function of doping and ligand engineering to enhance the photostability and electroluminescence performance of CsPbBr3 quantum dots

The photostability issue of CsPbX3 (X = Cl, Br, I) quantum dots (QDs) is one of the key origins for the degradation of their luminescence performance, which hinders their application in lighting and displays. Herein, we report a new method combining doping and ligand engineering, which effectively improves the photostability of CsPbBr3 QDs and the performance of QD light-emitting diodes (QLEDs). In this method, ZnBr2 is doped into CsPbBr3 QDs to reduce surface anion defects; didodecyldimethyl ammonium bromide (DDAB) and tetraoctylammonium bromide (TOAB) hybrid ligands, which have strong adsorption with QDs, are employed to protect the surface and enhance the conductivity of QD layer in QLEDs. The photoluminescence (PL) and transmission electron microscopy measurements prove the effectively improved photostability of CsPbX3 QDs. Moreover, reduced defects and improved conductivity by doping and hybrid ligands treatment also enable the improved electroluminescence performance of CsPbX3 QDs. The maximum luminance and external quantum efficiency of the QLED with optimized CsPbX3 QDs are 3518.9 cd m−2 and 5.07%, which are 3.6 and 2.1 times than that of the control device, respectively. Combining doping and hybrid ligands makes perovskite QDs have an extremely promising prospect in future applications of high-definition displays, high-quality lighting, as well as solar cells.

Perovskite CsPbX3 (X=Cl, Br, I) Nanocrystals in fluorophosphate glasses

For the first time, CsPbX3 (X=Cl, Br, I) nanocrystals (NCs) are synthesized in fluorophosphate glasses. The controlled formation of CsPbX3 quantum dots is realized by adjustment of cooling rate and heat treatment conditions. X-ray diffraction data and optical measurements have confirmed the formation of 4-11 nm sized CsPbX3 nanocrystals. The crystallization of CsPbCl3 is assumed to proceed according to a heterogeneous mechanism, with small CsPbBr NCs acting as nuclei. The introduction of two anions (Cl, Br or Br, I) has results in the appearance of two narrow bands in the luminescence spectra corresponding to quantum dots with different chemical compositions, suggesting that the preparation of NCs with a mixed anion is complicated by phase segregation during the high-temperature synthesis. The photoluminescence of CsPb(Cl, Br)3 quantum dots has a high intensity with a quantum yield of 45-50 % and narrow emission band.

Na-doping CsPbBr3 quantum dots prepared via ion exchange for bright and stable blue-to-red photoluminescence

The low photoluminescence (PL) efficiency and bad stability have been great attention for CsPbX3 quantum dots (QDs). In this work, sodium ions (Na+) derived ion exchange for CsPbBr3 QDs was tested to study the tunable PL and stability. After doping with Na+ ions, the PL quantum yields (PLQYs) of CsPbBr3 QDs was increased from 52.6 to 94.3%. Various characteristics confirm Na+ ions occupied the position of cesium (Cs) position in CsPbBr3. The blue-shifted PL peaks from Na:CsPbBr3 QDs further proved that Na+ ions were successfully incorporated into the lattices of CsPbBr3. The stability test indicates that the introduction of Na+ ions improved the chemical environment of CsPbBr3 QDs to prevent the PL quenched. Finally, the post-treatment of PbCl2 and PbI2 solution was used to conduct anion exchange reaction of Na:CsPbBr3. The PL in whole visible light region was obtained by controlling the exchange amount of I and Cl ions. The PLQYs and stability of the QDs was further improved especially for red-emitting perovskite QDs. The high PLQYs and the PL in whole visible light region make an important application in imaging. This work provides a new approach for getting high PLQYs and adjusting PL spectra from perovskite QDs.

Correction: The dual-defect passivation role of lithium bromide doping in reducing the nonradiative loss in CsPbX3 (X = Br and I) quantum dots

Correction for ‘The dual-defect passivation role of lithium bromide doping in reducing the nonradiative loss in CsPbX3 (X = Br and I) quantum dots’ by Hao Wu et al., Inorg. Chem. Front., 2020, DOI: 10.1039/d0qi01262a.

Transient Optical Properties of CsPbX3/Poly(maleic anhydride‐alt‐1‐octadecene) Perovskite Quantum Dots for White Light‐Emitting Diodes

Poly(maleic anhydride‐alt‐1‐octadecene) (PMAO)‐coated green CsPbBr3 and red CsPbBr0.6I2.4 quantum dots (QDs), as the phosphor materials for white light‐emitting diodes (WLEDs), are reported. The anhydride groups of PMAO can be bound to the surface ligands of perovskite QDs and act as a protective layer. The results show that CsPbX3/PMAO (X = Cl, Br, I) presents good crystallinity and excellent luminescence properties. Time‐resolved photoluminescence (TRPL) shows that the PL lifetime of CsPbX3/PMAO is prolonged, and the transient absorption (TA) results show that intraband hot‐exciton relaxation and exciton recombination can be slowed down when the CsPbX3 QDs are coated with PMAO. However, the PL quantum yields (PLQYs) increase for both the green‐emitting QDs and the red‐emitting QDs after PMAO coating. WLED devices are fabricated by integrating the green CsPbBr3/PMAO QDs and red CsPbBr0.6I2.4/PMAO QDs on the blue GaN chips. The devices show stable white light emission with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.314, 0.291). The results indicate that CsPbX3/PMAO QDs can be an ideal downconversion fluorescent material for WLED devices.