Modifying both the top and bottom surfaces of CsPbBr3 perovskite films enhances carrier lifetime and optical gain remarkably.

All-inorganic perovskites such as CsPbX 3 have attracted huge attention because of its superior stability. [6] So far, perovskite nanowires, microplates, and films have been used to realize lasing or amplified spontaneous emission (ASE). Both lasing and ASE are a kind of light amplification through stimulated emission when there is an inverted population between two energy states. [7] Stimulated emission is that an incident single photon stimulates other recombination and creates an additional photon which is exactly the same as oneself. [8] When the excitation fluence exceeds a certain threshold and population inversion is achieved, the probability of generating stimulated emission is greater than that of absorption for an incident photon, thus realizing light amplification and optical gain. ASE or lasing will occur only if optical gain is larger than optical loss. [7a] Unlike lasers, ASE does not require a resonant cavity. [7b,9] That is, it is necessary to construct the resonant cavity for the transformation from ASE to lasing. Remarkably, perovskite nanowires [10] and microplates [11] can use their own nanostructures as resonant cavities to amplify light and achieve lasing. However, the difficulties in precise position control largely limit their integration with other optical and electrical devices. [12] By contrast, perovskite films are simple to prepare and easy to integrate with other optical and electronic devices. [12,13] Lasing or ASE based on CsPbX 3 films have been demonstrated in red and green spectral regions. [6b,13,14] However, there are few report about blue lasing or ASE based on CsPbX 3 film. The factors restricting the realization of blue lasing or ASE are the preparation of high-quality films and the improvement of spectral stability. On the one hand, the low solubility of chlorine sources such as CsCl in the precursor aggravates the fabrication of the films, [15] which lead to poor quality of films and more scattering losses. On the other hand, the mixed halides perovskites generally undergo ion migration under the stimuli of light or electric filed, resulting in phase separation and spectral instability. [16] Especially, ion migration will be more obvious under high flux excitation needed for reaching population inversion. [17] Therefore, it's of great significance to prepare high-quality thin films with good spectral stability for blue ASE or laser.In this work, we demonstrate blue ASE from mixed-Br/Cl quasi-2D Cs-based perovskite films prepared by a facile vapor anion exchange (VAE) method. Unlike the method of directly Solution-processed all-inorganic CsPbX 3 perovskites exhibit outstanding optoelectronic properties and are being considered as a promising optical gain medium, with impressive performance in the green and red region. However, the development of CsPbX 3 for blue emission is still lagging far behind, owing to difficulties in thin films synthesis and spectral instability subject to light irradiation. Here, a facile vapor anion exchange (VAE) method that enables pr...

Background The neuroimaging manifestations of eclampsia and preeclampsia often overlap, mainly presenting as posterior reversible encephalopathy syndrome (PRES). The purpose of this retrospective study was to compare the extent and nature of brain edema in eclampsia and preeclampsia patients with PRES based on MRI characteristics. Methods One hundred fifty women diagnosed with preeclampsia-eclampsia and undergoing cranial MRI were enrolled; 24 of these were diagnosed as having eclampsia. According to clinicoradiologic diagnosis of PRES, eligible patients were classified as having eclampsia with PRES (group E-PRES) and preeclampsia with PRES (group P-PRES). A scale on T2W FLAIR-SPIR images was established to evaluate the extent of brain edema, and the score of brain edema (SBE) of both groups was compared. In patients of the two groups who also underwent DWI sequence, the presence or absence of hyperintensity on DWI and hypointensity on ADC maps were determined to compare the nature of brain edema. Furthermore, clinical and biochemical data of the two groups were compared. Results The incidence of PRES in eclampsia patients was significantly higher than that in preeclampsia patients (87.50% vs. 46.03%, P<0.001). The SBE of all regions and typical regions in group E-PRES patients were significantly higher than those in group P-PRES patients (15.88±8.72 vs. 10.90±10.21, P=0.021; 8.52±3.87 vs. 5.01±4.19, P=0.002; respectively). The presence of hyperintensity on DWI was determined more frequently in group E-PRES patients than group P-PRES patients (71.43% vs. 32.00%, P=0.024). Age, systolic blood pressure, white blood cell count, neutrophil count and percentage of neutrophils were significantly different between the two groups (P<0.05). Conclusions Certain MRI characteristics that reflect the extent and nature of brain edema were different between eclampsia and preeclampsia patients with PRES. Additional prospective studies are still required to explore whether these MRI characteristics of brain edema may further become a potential predictor for eclamptic seizures in preeclampsia patients with PRES.