Multimode Luminescence with Temperature and Energy Level Synergistic Dependence in Rare Earth Halide DPs for Advanced Multifunctional Applications.

Rare-earth halide double perovskites (DPs) have attracted extensive attention due to their excellent optoelectronic performance. However, the correlation between luminescence performance, crystal structure, and temperature, as well as the inherent energy transfer mechanism, is not well understood. Herein, Lanthanide ions (Ln3+: Nd3+ or Dy3+) as the co-dopants are incorporated into Sb3+ doped Cs2NaYbCl6 DPs to construct energy transfer (ET) models to reveal the effects of temperature and energy levels of rare earth on luminescence and ET. The different excited state structures of Sb3+-Ln3+ doped Cs2NaYbCl6 DPs at different temperatures and relative positions of energy levels of rare earth synergistically determine the physical processes of luminescence. These multi-mode luminescent materials exhibit good performance in anti-counterfeiting, NIR imaging, and temperature sensing. This work provides new physical insights into the effects of temperature and energy levels of rare earth on the energy transfer mechanism and related photophysical process.

The luminescence modulation of rare earth-doped/containing lead-free double perovskites toward multifunctional applications: a review.

Lead-free double perovskites (DPs) with superior environmental stability and high defect tolerance have attracted considerable attention and exhibit great promise in photodetectors, solar cells, lighting devices, etc. However, achieving optical modulation and high photoluminescence quantum yield using this kind of material remains a challenge. Rare earth ions feature abundant energy levels and outstanding photophysical properties. Incorporating rare earth ions into lead-free DPs is an effective strategy to improve their optical performances, which have great effects on night-vision and light emitting diodes. Consequently, in this mini-review, we summarize the synthesis methods, optical properties, issues, and multifunctional applications of lead-free DPs described in recent years. The performances of DPs can be modulated via rare earth doping, which involves the extension of luminescence range, the improvement of PLQY, the realization of multi-mode excitation, and the regulation of luminescence color. We hope that this review will provide some insights into luminescence modulation and applications of lead-free DPs.

Excited State Regulated Emission in Hybrid Indium Halides via Crystal Structure Switch.

Organic-inorganic metal halides have become one of the most promising materials in the next generation of optoelectronic applications due to their high charge carrier mobility and tunable band gaps. In this study, Sb:PA6InCl9 and Sb:PA4NaInCl8 single crystals were prepared through evaporation crystallization, respectively. Due to the different degrees of lattice distortions, the highly efficient yellow emission in Sb:PA6InCl9 at 610 nm and the green emission in Sb:PA4NaInCl8 at 545 nm were achieved by regulation of the excited state, respectively. By introducing additional sodium ions in the post-treatment, we found that the zero-dimensional Sb:PA6InCl9 could rapidly convert into a two-dimensional layered structure of Sb:PA4NaInCl8, thus resulting in a novel green/yellow emission switch. This work guides the structural and performance control of organic-inorganic hybrid In-based metal halides and offers broad prospects for luminescent switching in anticounterfeiting applications.

Alkaline surface treatment and time-resolved reading of mn-doped nanocrystal signal transducer for enhanced bioassay sensitivity.

Recently, Mn-doped semiconductor nanocrystals (NCs) with high brightness, long lifetimes, and low-energy excitation are emerging for time-resolved luminescence biosensing/imaging. Following our previous work on Mn-doped NCs, in this work we developed poly(styrene-co-maleic anhydride) (PSMA)-encapsulated Mn-doped AgZnInS/ZnS NCs as signal transducers for immunoassay of capsular polysaccharide (CPS), a surface antigen and also a biomarker of Burkholderia pseudomallei which causes a fatal disease called melioidosis. To enhance the assay sensitivity, a surface treatment for PSMA-encapsulated NCs (NC-probes) was performed to promote the presence of carboxyl groups that help conjugate more anti-CPS antibodies to the surface of NC-probes and thus enhance bioassay signals. Meanwhile, time-resolved reading on the luminescence of NC-probes was adopted to minimize the assay background autofluorescence. Both strategies essentially enhance the assay signal-to-background ratio (or equivalently the assay sensitivity) by increasing the signal and decreasing the background, respectively. Through performing and comparing immunoassays with different NC-probes (with and without surface treatment) and different signal reading methods (time-resolved reading and non-time-resolved reading), it was proven that the immunoassay adopting surface-treated NC-probes and time-resolved reading achieved a lower limit-of-detection (LOD) than the ones adopting non-surface-treated NC-probes or non-time-resolved reading. Moreover, the achieved LOD is comparable to the LOD of immunoassay using enzyme horseradish peroxidase as a signal transducer.

Photocatalytic CO2 Reduction Coupled with Oxidation of Benzyl Alcohol over CsPbBr3@PANI Nanocomposites.

Herein, we successfully prepare conductive polyaniline (PANI)-encapsulated CsPbBr3 perovskite nanocrystals (PNCs) that demonstrate much improved photocatalytic performance and stability toward the CO2 reduction reaction (CRR) coupled with oxidation of benzyl alcohol (BA) to benzaldehyde. Due to the acid-base interaction between CO2 and PANI, CO2 molecules are selectively adsorbed on PANI in the form of carbamate. As a result, the rate of production of CO (rCO) reaches 26.1 µmol g-1 h-1 with a selectivity of 98.1%, which is in good agreement with the rate of oxidation (∼27.0 µmol g-1 h-1) of BA. Such a high reduction/oxidation rate is enabled by the fast electron transfer (∼2.2 ps) from PNCs to PANI, as revealed by femtosecond transient absorption spectroscopy. Moreover, because of the benefit of the encapsulation of PANI, no significant decrease in rCO is observed in a 10 h CRR test. This work offers insight into how to simultaneously achieve improved photocatalytic performance and stability of CsPbX3 PNCs.

Effective Energy Transfer Boosts Emission of Rare-Earth Double Perovskites: The Bridge Role of Sb(III) Doping.

Halide perovskites have attracted considerable interest due to their excellent photoelectric properties. In this study, we synthesized Sb3+-doped Cs2NaTbCl6 using a solvothermal method to investigate its tunable photoelectric properties and low toxicity. Upon Sb3+ ion doping, the photoluminescence yield (PLQY) of Cs2NaTbCl6 significantly increased from ∼1.7 to ∼47%. The introduced Sb3+ ions with ns2 electronic configuration expanded the rare-earth element's absorption cross section, broke intrinsic forbidden transitions, and suppressed nonradiative recombination. Additionally, the codoping of Sb3+ and Mn2+ facilitated efficient energy transfer, resulting in highly efficient photoluminescence. The PLQY of 1%Sb3+,3%Mn2+:Cs2NaTbCl6 reached a remarkable 85.8%, marking the highest reported value for rare-earth double perovskites in the visible light region. This study highlights the vital role of Sb(III) doping as a bridging agent to enhance the emission in rare-earth double perovskites.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic-Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides.

Organic-inorganic metal halides (OIMHs) have abundant optical properties and potential applications, such as light-emitting diodes, displays, solar cells, and photodetectors. Herein, we report zero-dimensional Mn-based OIMH (C8H20N)2MnCl4 single crystals synthesized by a simple slow evaporation method, which exhibit intense green emission at 520 nm originating from 4T1-6A1 transition of Mn2+ ions. Large organic cations in the crystal structure result in the isolated [MnCl4]2- tetrahedrons, and the closest Mn-Mn distance reaches 9.07 Å, which effectively inhibits the migration of excitation energy between adjacent Mn2+ emission centers, thus achieving a high quantum yield (∼87%) and a long photoluminescence (PL) lifetime (3.42 ms). The different optical and structural properties at low and high temperatures are revealed by temperature-dependent PL and X-ray diffraction spectra. The PL spectra and lifetimes under the heating and cooling processes indicate that the optical property transitions are reversible at 220/240 K. Our work provides a promising strategy for building multifunctional optoelectronic materials and insights into the understanding convertible photophysical properties from isomers of metal halides.

Weakening Ligand-Liquid Affinity to Suppress the Desorption of Surface-Passivated Ligands from Perovskite Nanocrystals.

The interfacial migration of surface-bound ligands highly affects the colloidal stability and optical quality of semiconductor nanocrystals, of which the underlying mechanism is not fully understood. Herein, colloidal CsPbBr3 perovskite nanocrystals (PNCs) with fragile dynamic equilibrium of ligands are taken as the examples to reveal the important role of balancing ligand-solid/solvent affinity in suppressing the desorption of ligands. As a micellar surfactant, glycyrrhizic acid (GA) with bulky hydrophobic and hydrophilic groups exhibits a relatively smaller diffusion coefficient (∼440 µm2/s in methanol) and weaker ligand-liquid affinity than that of conventional alkyl amine and carboxy ligands. Consequently, hydrophilic GA-passivated PNCs (PNCs-GA) show excellent colloidal stability in various polar solvents with dielectric constant ranging from 2.2 to 32.6 and efficient photoluminescence with a quantum yield of 85.3%. Due to the suppressed desorption of GA, the morphological and optical properties of PNCs-GA are well maintained after five rounds purification and two months long-term storage. At last, hydrophilic PNCs-GA are successfully patterned through inkjet- and screen-printing technology. These findings offer deep insights into the interfacial chemistry of colloidal NCs and provide a universal strategy for preparing high-quality hydrophilic PNCs.

Competing Energy Transfer in Two-Dimensional Mn2+-Doped BDACdBr4 Hybrid Layered Perovskites with Near-Unity Photoluminescence Quantum Yield.

Two-dimensional (2D) hybrid layered perovskites (HLPs) have attracted extensive attention due to their excellent optoelectronic properties. Herein, we successfully prepared high-quality Mn-doped BDACdBr4 (BDA = NH2(CH2)4NH2, butylene diammonium) HLP single crystals (SCs). The incorporation of Mn2+ ions modulates the electronic band structure of BDACdBr4 perovskites and tailors the energy transfer process of excited states. A near-unity photoluminescence (PL) quantum yield of 96% from the Mn2+ emission at 608 nm is achieved. Excitation wavelength-dependent spectroscopic characterizations help to clarify the energy transfer mechanism of Mn-doped BDACdBr4, in which competing PL from the 3Eg → 1A1g transition of Cd2+ and the 4T1(G) → 6A1(S) transition of Mn2+ dopants is observed. Temperature-dependent PL spectroscopic characterizations indicate that the efficient energy transfer from BDACdBr4 perovskite host to Mn2+ dopants requires thermal activation to overcome a potential barrier. This work provides new insight into the photophysics and optical properties of 2D HLPs, especially the influence of Mn2+ doping on competing energy transfer in hybrid luminescent materials.

Competing Energy Transfer-Modulated Dual Emission in Mn2+-Doped Cs2NaTbCl6 Rare-Earth Double Perovskites.

A2BIBIIIX6 double perovskites are promising materials due to their outstanding photoelectronic properties and excellent stability in the environment. Herein, we synthesized Mn2+:Cs2NaTbCl6 with dual emission through a solvothermal method for the first time. Mn2+:Cs2NaTbCl6 double perovskites exhibit excellent environmental stability and high photoluminescence quantum yields (PLQYs). The Cs2NaTbCl6 was successfully doped with Mn2+ in two modes: at Mn-feeding concentrations below 1%, Mn2+ first tend to insert into the interstitial void, but if the Mn-feeding concentration exceeds 1%, Mn2+ will further substitute Na+ site of the Cs2NaTbCl6 lattice and thus both two doping modes coexist. After Mn2+ doping, efficient energy transfer from the 5D4 level of Tb3+ ions to the 4T1 level of Mn2+ ions occurs, resulting in tunable dual emission from the Tb3+5D4 → 7FJ=6,5,4,3 transition and Mn2+4T1 → 6A1 transition. Further, LED based on the Mn2+:Cs2NaTbCl6 double perovskites exhibits excellent performance and stability. This work demonstrates a strategy to achieve novel lanthanide-based double perovskites with potential applications in photonics.

Green Triplet Self-Trapped Exciton Emission in Layered Rb3Cd2Cl7:Sb3+ Perovskite: Comparison with RbCdCl3:Sb3.

Metal halide materials have recently sparked intense research because of their excellent photophysical properties and chemical stability. For example, RbCdCl3:Sb3+ exhibits broad emission at about 600 nm with a high photoluminescence quantum yield (PLQY) over 91% and double emission bands with bright white color. Herein, we obtained a novel Rb and Cd layered perovskite Rb3Cd2Cl7 doped with Sb3+, which gives luminescence at 525 nm with a large Stokes shift of 200 nm, originating from a self-trapped exciton (STE). Its PLQY is 57.47%, but its low-temperature PLQY becomes much higher at the same wavelength. When Rb3Cd2Cl7:Sb3+ and RbCdCl3:Sb3+ were compared, the two classes of quantum confinement effects by Rb and Cd ions in the lattice were identified to describe their electronic states and different optical properties. These results suggest that properties of Sb-doped cadmium halides could be modified by the structure type and local atomic confinement to find applications as promising luminescent materials for optoelectronic devices.

Efficient Orange Emission in Mn2+-Doped Cs3Cd2Cl7 Perovskites with Excellent Stability.

Low-dimensional metal halides are attractive for applications in photodetectors, solid-state lighting, and solar cells, but poor stability is an obstacle that must be overcome in commercial applications. Herein, we successfully synthesized a Ruddlesden-Popper (RP)-phased perovskite Mn2+:Cs3Cd2Cl7 with high photoluminescence quantum yield (PLQY) and outstanding thermal and environmental stability by a solvothermal method. The pristine sample Cs3Cd2Cl7 exhibits a weak cyan broad emission centered at 510 nm with a low PLQY of ∼4%. Once Mn2+ ions are introduced into the host lattice, a bright orange emission peaking at 580 nm with a high PLQY of ∼74% was achieved, which is attributed to the efficient energy transfer from the host to Mn2+ ions and thus results in the 4T1 → 6A1 radiation transition of Mn2+ ions. The photoluminescence (PL) intensity and environmental stability of Mn2+:Cs3Cd2Cl7 can be further improved through A-site Rb alloying. Finally, an orange LED with outstanding color stability was fabricated on the basis of the Mn2+:Cs3Cd2Cl7. Our work successfully elucidates that dopant plays an integral role in tailoring optical properties.

Tunable Green Light-Emitting CsPbBr3 Based Perovskite-Nanocrystals-in-Glass Flexible Film Enables Production of Stable Backlight Display.

Despite recent advances in producing perovskite-nanocrystals-in-glass (PNG) for display application, it remains challenging to achieve ultrapure and large-area CsPbBr3 PNG-based flexible films with tunable green emission. Herein, we report a facile strategy to produce flexible film containing CsPbBr3 PNG. Specifically, the achievement of CsPbBr3 PNG with tunable green emissions (517-528 nm) is realized by elaborate regulation of the glass precursor concentration and thermal treatment temperature by an in situ growth method. With the integration of red-light-emitting CsPbBrxI3-x PNG powder, the color gamut of as-prepared white-light-emitting sources can cover up to 126.27% of the NTSC 1953 standard and 93.9% of the Rec. 2020 standard. Notably, flexible and large-area white-light-emitting films can be readily obtained by sandwiching and gluing mixed PNG powders between two layers of hydrophobic and transparent PET films. Intriguingly, as-prepared PNG films exhibit excellent hydrothermal, photostability, and long-term operation stability, making them promising for practical ultrahigh-definition displays.

Highly efficient green InP-based quantum dot light-emitting diodes regulated by inner alloyed shell component.

InP-based quantum dot light-emitting diodes (QLEDs), as less toxic than Cd-free and Pb-free optoelectronic devices, have become the most promising benign alternatives for the next generation lighting and display. However, the development of green-emitting InP-based QLEDs still remains a great challenge to the environmental preparation of InP quantum dots (QDs) and superior device performance. Herein, we reported the highly efficient green-emitting InP-based QLEDs regulated by the inner alloyed shell components. Based on the environmental phosphorus tris(dimethylamino)phosphine ((DMA)3P), we obtained highly efficient InP-based QDs with the narrowest full width at half maximum (~35 nm) and highest quantum yield (~97%) by inserting the gradient inner shell layer ZnSexS1-x without further post-treatment. More importantly, we concretely discussed the effect and physical mechanism of ZnSexS1-x layer on the performance of QDs and QLEDs through the characterization of structure, luminescence, femtosecond transient absorption, and ultraviolet photoelectron spectroscopy. We demonstrated that the insert inner alloyed shell ZnSexS1-x provided bifunctionality, which diminished the interface defects upon balancing the lattice mismatch and tailored the energy levels of InP-based QDs which could promote the balanced carrier injection. The resulting QLEDs applying the InP/ZnSe0.7S0.3/ZnS QDs as an emitter layer exhibited a maximum external quantum efficiency of 15.2% with the electroluminescence peak of 532 nm, which was almost the highest record of InP-based pure green-emitting QLEDs. These results demonstrated the applicability and processability of inner shell component engineering in the preparation of high-quality InP-based QLEDs.

Phase-Selective Solution Synthesis of Cd-Based Perovskite Derivatives and Their Structure/Emission Modulation.

The rich phase structures of perovskite derivatives have attracted extensive attention and can be applied in the fields of optoelectronics due to their high emission efficiency and tunable emission. Herein, we explored a phase-selective solution synthetic route to obtain different Cd-based perovskite derivatives. First, the pristine tetragonal Cs7Cd3Br13 was obtained by a solvothermal method, and its photoluminescence quantum yield (PLQY) was boosted from 8.28% to 57.62% after appropriate Sb3+ doping. Furthermore, halogen substitution was adopted to modify Sb:Cs7Cd3Br13 and produced a series of Cd-based perovskite derivatives with different crystal structures and tunable emission from cyan to orange (517-625 nm). The mechanisms behind such experimental phenomena were further investigated and discussed on the basis of material characterization and theoretical computation. This study presented an effective strategy to synthesize bright Cd-based perovskite derivatives with different structures and modulated emission, and it also provided insights to understand the structure/emission modulation via halogen substitution.

Component Engineering to Tailor the Structure and Optical Properties of Sb-Doped Indium-Based Halides.

Controlling the structure of halide perovskites through component engineering, and thus revealing the changes in luminescence properties caused by the conversion of crystal structure, is of great significance. Herein, we report a controllable synthetic strategy of three-dimensional (3D) Cs2KInCl6 and zero-dimensional (0D) (Cs/K)2InCl5(H2O) halide perovskites by changing the Cs/K feed ratio. 3D Cs2KInCl6 double perovskites are obtained at the Cs/K feed ratio of 1:1, while 0D (Cs/K)2InCl5(H2O) perovskites are formed at the Cs/K feed ratio of 2:1. Further, a reversible crystal structure transformation between 3D Cs2KInCl6 double perovskites and 0D (Cs/K)2InCl5(H2O) perovskites can be achieved by subsequent addition of metal-salt precursors. In addition, the emission efficiency of two perovskite structures can be greatly boosted by breaking the forbidden transition through Sb doping, and as a result, a novel green/yellow reversible emission switch is generated. Meanwhile, the relationship between perovskite structure and luminescence mechanism has been systematically revealed. These environmentally stable halide perovskites have great potential to be applied in optoelectronic devices.

Review of Mn-Doped Semiconductor Nanocrystals for Time-Resolved Luminescence Biosensing/Imaging.

Colloidal semiconductor nanocrystals (NCs) have been developed for decades and are widely applied in biosensing/imaging. However, their biosensing/imaging applications are mainly based on luminescence-intensity measurement, which suffers from autofluorescence in complex biological samples and thus limits the biosensing/imaging sensitivities. It is expected for these NCs to be further developed to gain luminescence features that can overcome sample autofluorescence. On the other hand, time-resolved luminescence measurement utilizing long-lived-luminescence probes is an efficient technique to eliminate short-lived autofluorescence of samples while recording time-resolved luminescence of the probes for signal measurement after pulsed excitation from a light source. Despite time-resolved measurement being very sensitive, the optical limitations of many of the current long-lived-luminescence probes cause time-resolved measurement to be generally performed in laboratories with bulky and costly instruments. In order to apply highly sensitive time-resolved measurement for in-field or point-of-care (POC) testing, it is essential to develop probes possessing high brightness, low-energy (visible-light) excitation, and long lifetimes of up to milliseconds. Such desired optical features can significantly simplify the design criteria of time-resolved measurement instruments and facilitate the development of low-cost, compact, sensitive instruments for in-field or POC testing. Mn-doped NCs have recently been in rapid development and provide a strategy to solve the challenges faced by both colloidal semiconductor NCs and time-resolved luminescence measurement. In this review, we outline the major achievements in the development of Mn-doped binary and multinary NCs, with emphasis on their synthesis approaches and luminescence mechanisms. Specifically, we demonstrate how researchers approached these obstacles to achieve the aforementioned desired optical properties on the basis of the progressive understanding of Mn emission mechanisms. Afterward, we review representative applications of Mn-doped NCs in time-resolved luminescence biosensing/imaging and present the potential of Mn-doped NCs in advancing time-resolved luminescence biosensing/imaging for in-field or POC testing.

Mg2+-Assisted Passivation of Defects in CsPbI3 Perovskite Nanocrystals for High-Efficiency Photoluminescence.

CsPbI3 perovskite nanocrystals (NCs) are emerging as promising materials for optoelectronic devices because of their superior optical properties. However, the poor stability of CsPbI3 NCs has become a huge bottleneck for practical applications. Herein, we report an effective strategy of Mg2+-assisted passivation of surface defects to obtain high emission efficiency and stability in CsPbI3 NCs. It is found that the introduced Mg2+ ions are mainly distributed on the surface of NCs and then passivate the NC defects, enhancing radiative decay rate and reducing nonradiative decay rate. As a result, the as-prepared Mg2+-treated CsPbI3 (Mg-CsPbI3) NCs exhibit the highest photoluminescence quantum yield (PLQY) of 95%. The Mg-CsPbI3 NC colloidal solution retains 80% of its original PLQY after 80 days of atmosphere exposure. The red perovskite light-emitting diodes based on the Mg-CsPbI3 NCs demonstrate an external quantum efficiency of 8.4%, which shows an almost 4-fold improvement compared to the devices based on the untreated NCs.

Reversible Zn2+ Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows.

Zinc-anode-based electrochromic devices (ZECDs) are emerging as the next-generation energy-efficient transparent electronics. We report anatase W-doped TiO2 nanocrystals (NCs) as a Zn2+ active electrochromic material. It demonstrates that the W doping in TiO2 highly reduces the Zn2+ intercalation energy, thus triggering the electrochromism. The prototype ZECDs based on W-doped TiO2 NCs deliver a high optical modulation (66% at 550 nm), fast spectral response times (9/2.7 s at 550 nm for coloration/bleaching), and good electrochemical stability (8.2% optical modulation loss after 1000 cycles).