RESUMEN
In this study, bulk modulus of a colloidal crystal formed by highly charged particles is experimentally determined by applying direct current electric field. A theoretical expression is also proposed to independently predict the bulk modulus based on van't Hoff's law of osmotic pressure and the theory of Ohshima. The experimental result thus obtained agrees well with the theoretical expectation. In addition, results from both above-mentioned methods coincide with that inferred from the static structure factor.
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ITO/Y2O3/Ag devices were fabricated using Y2O3 films as insulator. Four intense and sharp lines with half-peak width of 4 nm were observed for the 293.78 nm InI, 316.10 nm InI, 444.82 nm InII and 403.07 nm InIII transitions. Luminescence mechanism was illustrated by cross-section of the devices based on the analysis of surface morphology. Under the action of strong electric field, the loss of K-shell electrons led to the occurrence of characteristic radiation of indium ions. In addition, the device with turn-on voltage of 10V demonstrates typical I-V diode characteristics. Moreover, Y2O3/In2O3 multiple films as the insulation layer instead of single Y2O3 films was found to improve the device performance with excellent CIE (x, y) coordinates (0.16, 0.03).
RESUMEN
All-inorganic lead halide perovskite, characterized by its exceptional optical and electrical properties, is burgeoning as a potential optoelectronic material. However, the standalone CsPbBr3 component encounters several challenges including small exciton binding energy (≈40 meV) and long charge diffusion length, giving rise to low photo-luminescence quantum-yield (PLQY); ion migration leads to instability in device operation, hindering device operation and potential development. To circumvent these limitations, our research endeavors to construct a novel core-shell structure that transforms the continuous [PbX6]4- octahedron into an isolated octahedral structure. We introduce the Cs4PbBr6 phase with 0D structure to passivate the vacancy defects in CsPbBr3, thereby suppressing ion migration and enhancing the luminescence intensity and stability. Our methodology involves fabricating dense CsPbBr3-Cs4PbBr6 composite films using a co-evaporation method, wherein the molar ratio of CsBr and PbBr2 is precisely adjusted. The films are subsequently rapidly annealed under ambient air conditions, and the effects of different annealing temperatures and annealing times on the CsPbBr3-Cs4PbBr6 films were investigated. Our results demonstrate significantly improved stability of the annealed films, with a mere 15% decrease in PL intensity after 100 days of storage under ambient air conditions at 48% relative humidity (RH). Based on this thin film, we fabricated all-inorganic structure Ag/N-Si/CsPbBr3-Cs4PbBr6/NiO/ITO light emitting diodes (LEDs), the devices have a low turn-on voltage VT â¼3 V and under unencapsulated, ambient air conditions, it can operate continuously for 12 hours under DC drive with only 10% attenuation. The results we obtained open up the possibility of designing and developing air-stable perovskite LEDs.
RESUMEN
The all-inorganic lead halide perovskite has become a very promising optoelectronic material due to its excellent optical and electrical properties. Device performances are currently hindered by crystallinity of the films and environmental stability. Here, we adopted dual-source co-evaporation method to prepare CsPbBr3 films. By adjusting and controlling the co-evaporation ratio and substrate temperature, we obtained CsPbBr3 films with large grain sizes and uniform morphology. Films with smooth surfaces and large grains exhibit properties such as efficient photon capture, fast carrier transport, and suppressed ion migration. Therefore, in this paper, by refining the annealing conditions, the effects of annealing temperature and time on the films were studied in detail. The CsPbBr3 films were annealed under suitable annealing temperature and time in ambient air, and films with high quality and crystallinity and average grain size up to ~ 2.5 µm could maintain stability in ambient air for 130 days. The corresponding LEDs show the full width at half maximum (FWHM) of the green EL spectrum is as narrow as 18 nm, and the devices have a low turn-on voltage VT ~ 3 V and can work continuously for 12 h in ambient air.
RESUMEN
CeO2/Tb4O7 superlattices were deposited on P type Si wafers by e-beam evaporation technology. Four typical photoluminescence peaks of Tb3+ ions which located around 488, 544, 588 and 623 nm were obtained after the superlattices annealing in weak reducing atmosphere at high temperature. It was indicated that CeO2 films transferred to amorphous state as the valence transition of Ce4+ --> Ce3+ which was induced by thermal annealing, the energy transfer occurred between Ce3+ ions and Tb3+ ions, and the Tb3+ ions emition could be detected after obtaining the energy from Ce3+ ions. A study about the effect of Tb4O7 thickness on the superlattices photoluminescence showed that the maximum PL intensity as thickness of Tb4 O7 films were about 0.5 nm, the concentration quenching might occur because of the energy transfer among the Tb3+ ions. The annealing conditions research demonstrated that the maximum PL intensity could be obtained as the superlattices annealed at 1 200 degrees C for 2 hour. Further investigation inferred that the concentration of Ce3+ ions, Oxygen vacancy defects and the distance between Ce3+ ions and Tb3+ ions play an important role in the annealing process.
RESUMEN
Cadmium-based quantum dots (Cd-QDs) show decent performance for lighting applications due to good color saturation, an excellent high quantum yield, and a narrow full-width at half-maximum. However, the intrinsic toxicity of Cd is a major hindrance to related applications, especially in the biological field. ZnSe, with a band gap of 2.7 eV and lower toxicity than CdSe or CdS, is promising as a blue luminescent material. Herein, we mainly reported the preparation and luminescence properties of nanostructured ZnSe/ZnS multilayer thin films with bright blue photoluminescence. The photoluminescence spectrum contained two emission peaks, located at about 442 nm (near band-edge emission) and 550 nm (defect-related emission), respectively. More importantly, the photoluminescence performance and decay were explored in detail through low-temperature photoluminescence spectra. In addition, the nanostructured ZnSe/ZnS multilayer thin films showed favorable photostability.
RESUMEN
Compared to colloidal quantum dots, nanostructured multilayer films may also be a promising emission layer in future light-emitting diodes, due to their excellent photoluminescence (PL), narrow full width at half-maximum (FWHM), and wide color gamut. In this paper, multilayer-structured deep-blue light-emitting diodes (LEDs) were prepared, where nanostructured ZnSe/ZnS multilayer films act as the light-emitting layer. The device showed good blue electroluminescence (EL) spectrum locating at 448 nm with an FWHM of 31 nm. To improve the performance of the device, the effect of preparation parameters of different layers was investigated in detail. The results demonstrated that the preparation parameters of each layer affected the performance in different ways, and choosing the most suitable preparation parameters can achieve optimal performance. Furthermore, this multilayer-structured device based on nanostructured films as emission layer can also be applied in green and red LEDs or all-inorganic QLEDs.
RESUMEN
We investigated the evolution of concentration and phase structure of colloidal suspensions in a two-ends-open tube during drying process. The volume fraction and crystal structure of suspension in the capillary tube were determined by reflection spectrometer during drying process. Our experimental results show: (a) evaporation takes place in two directions of the tube, though much stronger in one direction than the other; (b) during drying process, colloidal suspension column along the tube can be divided into four regions, namely, the close packed region, concentrated region, initial concentration region and dilution region. A new model describing the evolution of concentration profile was proposed and the calculated results based on the model are in good agreement with the experimental ones. According to solute conservation, we also present a simple way to estimate the concentration of close packed region.
RESUMEN
In the present paper, SiO/SiO2 superlattices samples were prepared on Si substrates by electron beam evaporation. The samples were annealed in nitrogen atmosphere at high temperature subsequently. And then, Ce3+ ions with a dose of 2.0 x 10(14) and 2.0 x 10(15) cm(-2) respectively were implanted into these samples with formed Si nanocrystals. The photoluminescence (PL) spectra showed that the PL intensities of samples with Ce3+ implanting dropped sharply compared with the samples without Ce3+ implanting. The PL intensity increased gradually with increasing re-annealing temperature, but dropped again when the temperature exceeded 600 degrees C. The PL intensity even could be higher than that of samples without Ce3+ implanting if only the dose of Ce3+ was 2.0 x 10(14) cm(-2). When the dose of Ce3+ was 2.0 x 10(15) cm(-2), the PL intensity couldn't exceed that of samples without Ce3+ implanting even when the re-annealing temperature was 600 degrees C. Further investigations showed that the varieties of the PL intensities were mainly dependent on the re-annealing temperature, which had the best point at 600 degrees C, and the dose of Ce3+ had the right value. Furthermore, the experiment results proved that there was energy transfer from Ce3+ to Si nanocrystals in this kind of structure.
RESUMEN
SiO/SiO2 superlattices with different thickness of SiO and SiO2 films were deposited on the Si substrates at 200 degrees C by thermo-evaporation technology. The photoluminescence (PL) spectrum centers of the samples shifted from 400 nm to 600 nm with the increase in SiO films thickness. Similar phenomena were also found when increasing the thickness of SiO2 film but forming SiO film. It was found that the PL was attributed to the defects located at the interfaces between SiO and SiO2 films. The deconvolution of the PL spectra showed that the WOB(O3[triple bond]Si--O--O*), NOV(O3[triple bone]Si--Si[triple bond]O3), the E'center(O[triple bond]Si*) and NBOHC (O3[triple bond]Si--O*) defects contributed to the PL spectra. A mass of Si-O dangling bonds formed on the interfaces of the SiO and SiO2 during the deposition process, could provide many free O atoms and intrinsic defects. When the SiO film was thin (such as 1 nm), most of the Si6 rings were broken, and more WOB defects (415 nm) would be formed because of the combination of the intrinsic NBOHC defects and the diffusing O atoms on the interfaces. With the increase in the SiO film thickness, more Si6 rings were formed in the SiO films, that is the number of the Si-O dangling bonds decreased, less of WOB defects could be formed as both of the free O atoms and intrinsic defects decreased, but the NOV defects (470 nm) increased because of more E' center defects would be combined in pairs. With increasing of the SiO film thickness, the combination of the intrinsic defects became more difficult, so the E'center defects (520 nm) and NBOHC defects (630 nm) would dominate the PL of the SiO/SiO2 superlattices in turn. In conclusion, the evolution of the defects located at the interfaces induced the red shift of the PL
RESUMEN
Amorphous SiNx films were deposited on p-type Si(100)substrates by magnetron sputtering technology. The samples were then detected by a Bruker Tennsor 27 Fourier transform spectrometer. One intense absorption band of the SiNx films (from 812 to 892 cm(-1)) which was assigned to the stretching vibration mode of Si--N--Si bond was detected by Fourier transform infrared (FTIR) spectroscopy. Obviously, it was showed that a red shift of the absorption peak occurred in the FTIR spectrum with the sputtering power increasing; nevertheless, a blue shift of the absorption peak occurred after annealing with the temperature increasing. In the present paper, the deposition process and inner structures of the SiNx films were studied according to RBM (random bonding model)and CFM (central force model). With the increase in the ratio of N(Si)to N(N), the angle of the Si--N--Si changed and the different structures were formed correspondingly. Therefore the Si--Ny--Si(4-y) (0 < or = y < or = 4) models were set up to explain the inner structure of the SiNx films. The investigation showed that Si--N4 tetrahedron, Si--N--Si3, Si--N2--Si2, Si--N3--Si and Si--Si modes were formed accordingly in the SiNx films with the sputtering power increasing. And five models in total were formed during the deposition process. Different stretching vibration modes of Si--N--Si bond were corresponding to the different inner structures of thin films prepared by different sputtering power. With the temperature increasing, the activity of atoms increased which would let the angle of the Si--N--Si go to identical. As a result, Si3N4 and Si nanocrystals were formed with the phase separation of SiNx films during the annealing process with higher temperature, which would result in a blue shift to 870 cm(-1) (the standard absorption peak of Si3N4).
RESUMEN
SiO/SiO2 superlattices samples were prepared on Si substrates by reactive evaporation of SiO powder in vacuum or an oxygen atmosphere. The samples were annealed in nitrogen atmosphere at high temperature subsequently. And then, H+ with a dose of 3.0 x 10(14) x cm(-2) and 3.0 x 10(15) x cm(-2) respectively was implanted into these samples with formed Si nanocrystals at 20 keV. The PL spectra showed that the PL intensities of samples with H+ implanting dropped sharply compared with the samples without H+ implanting. The PL intensity increased gradually with increasing re-annealing temperature; and it even could exceed that of samples without H+ implanting if the dose of H+ was enough. Our further investigations showed that the varieties of the PL intensities were mainly dependent on the area density of the defects formed in the samples, and also the area density of the defects was influenced by the dose of H+ and the further re-annealing temperatures.
RESUMEN
Amorphous SiOx films were deposited on Si substrates by magnetron sputtering technology. Three absorption bands of the SiOx films were detected by Fourier transform infrared spectroscopy. The authors' investigation shows that Si-Oy-Si(4-y) (0 < y < or =4), Si6 rings, and non-bridging oxygen hole center defects were formed in the films with the sputtering power increasing. The appearance of the three absorption bands was due to the stretching and asymmetric stretching vibration of Si--O--Si bond and the vibration of O--Si--O bond corresponding to the above mentioned structures in the SiOx films.
RESUMEN
Great efforts have been devoted to achieving efficient Si-based light-emitting devices. Here we report new light-emitting devices fabricated with Tb2O3 on Si substrates. Intense green electroluminescence was observed, with a turn-on voltage of about 8 V. The green emission is attributed to the characteristic transitions of Tb3+ ions in Tb2O3. The electroluminescence mechanisms of the Tb2O3 light-emitting devices are discussed. In addition, visible and near infrared electroluminescence was observed in rare-earth (Eu3+, Sm3+ and Yb3+) doped Tb2O3 light-emitting devices.
RESUMEN
Rare-earth silicates are highly efficient materials for silicon-based light sources. Here we report a novel light-emitting device based on Ce2Si2O7. Intense violet/blue electroluminescence was observed, with a turn-on voltage of about 13 V. The violet/blue emission is attributed to 4f-5d transitions of the Ce(3+) ions in Ce2Si2O7, which are formed by interfacial reaction of CeO2 and Si. Electroluminescence and photoluminescence mechanisms of the Ce2Si2O7 light-emitting device are also discussed.