Scandium effect on the luminescence of Er-Sc silicates prepared from multi-nanolayer films

Optical Properties and First-Principles Study of CH3NH3PbBr3 Perovskite Structures

Solution-processed organic-inorganic hybrid perovskites have attracted attention as light-harvesting materials for solar cells and photonic applications. The present study focuses on cubic single crystals and microstructures of CH₃NH₃PbBr₃ perovskite fabricated by a one-step solution-based self-assembly method. It is seen that, in addition to the nucleation from the precursor solution, crystallization occurs when the solution is supersaturated, followed by the formation of a small nucleus of CH₃NH₃PbBr₃ that self-assembles into bigger hollow cubes. A three-dimensional (3D) fluorescence microscopy investigation of hollow cubes confirmed the formation of hollow plates on the bottom; then, the growth starts from the perimeter and propagates to the center of the cube. Furthermore, the growth in the (001) direction follows a layer-by-layer growth model to form a complete cube, confirmed by scanning electronic microscopy (SEM) observations. Two-dimensional (2D)-3D fluorescence microscopy and photoluminescence (PL) measurements confirm a peak emission at 535 nm. To get more insights into the structural and optical properties, density functional theory (DFT) simulations were conducted. The electronic and optical properties calculated by DFT are in agreement with the obtained experimental values. The density-of-state (DOS) calculations revealed that the valence band maximum (VBM) consists of states contributed by Br and Pb, which agrees with the X-ray photoelectron spectroscopy valence band (XPS VB) measurements.

Photoluminescence Studies of Rare Earth Doped Apatite Structured Phosphors

We developed novel phosphors based on Y₆Ba₄(SiO₄)₆F₂(YBSF) apatite doped with Dy³⁺. Phosphors with different doping concentrations of Dy³⁺ were prepared and their morphological, structural and spectral properties were analyzed. XRD pattern confirms the formation of Y₆Ba₄(SiO₄)₆F₂ apatite structured phosphors with space group P6₃/m and Debye scherrer formula gives the average crystalline size 33.4 nm. The morphological and topographical studies were done by FESEM and HRTEM analysis. EDX spectra show presence of all initial reactants in the final product. Photoluminescence spectra show two prominent peaks at 487 nm and 573 nm corresponding to magnetic dipole transitions (⁴F_9/2 → ⁶H_15/2) and electric dipole transitions (⁴F_9/2 → ⁶H_13/2) for 350 nm excitation wavelength. The chromaticity coordinate of the prepared phosphors was found to be in the region of near white light which shows that prepared phosphor are potential single phased phosphor for white light emitting diodes.

(Ca0.8Mg0.2Cl2/SiO2):Eu2+: a violet-blue emitting phosphor with a low UV content for UV-LED based phototherapy illuminators

A violet-blue emitting phosphor with a low UV content in its emission spectrum has been fabricated through cation substitution for UV-LED based phototherapy illuminators.

Selective Growth of Interface Layers from Reactions of Sc(MeCp)2(Me2pz) with Oxide Substrates

The transformation of an oxide substrate by its reaction with a chemical precursor during atomic layer deposition (ALD) has not attracted much attention, as films are typically deposited on top of the oxide substrate. However, any modification to the substrate surface can impact the electrical and optical properties of the device. We demonstrate herein the ability of a precursor to react deep within an oxide substrate to form an interfacial layer that is distinct from both the substrate and deposited film. This phenomenon is studied using a scandium precursor, Sc(MeCp)₂(Me₂pz) (1, MeCp = methylcyclopentadienyl, Me₂pz = 3,5-dimethylpyrazolate), and five oxide substrates (SiO₂, ZnO, Al₂O₃, TiO₂, and HfO₂). In situ Fourier transform infrared (FTIR) spectroscopy shows that at moderate temperatures (∼150 °C) the pyrazolate group of 1 reacts with the surface hydroxyl groups of OH-terminated SiO₂ substrates. However, at slightly higher temperatures (≥225 °C) typically used for the ALD of Sc₂O₃, there is a direct reaction between 1 and the SiO₂ layer, in addition to chemisorption at the surface hydroxyl groups. This reaction is sustained by sequential exposures of 1 until an ∼2 nm thick passivating interface layer is formed, indicating that 1 reacts with oxygen derived from SiO₂. A shift of the Si 2p core level position, measured by ex situ X-ray photoelectron spectroscopy, is consistent with the formation of a ScSi _xO _y layer. Similar observations are made following the exposure of a ZnO substrate to 1 at 275 °C. In contrast, Al₂O₃, TiO₂, and HfO₂ substrates remain resistant to reaction with 1 under similar conditions, except for a surface reaction occurring in the case of TiO₂. These striking observations are attributed to the differences in the electrochemical potentials of the elements comprising the oxide substrates to that of scandium. Precursor 1 can react with SiO₂ or ZnO substrates, since the constituent elements of these oxides have less-negative electrochemical potentials than do aluminum, titanium, and hafnium. Additionally, Sc₂O₃ and surface carbonates are deposited on all substrates by gas-phase reactions between 1 and residual water vapor in the reactor. The extent of gas-phase reactions contributing to film growth is governed by the relative pressure of water vapor in the presence of 1. These results suggest caution when using very reactive, oxophilic precursors such as 1 to avoid misinterpreting unconventional film deposition as that resulting from a standard ALD process.

Effect of structure and composition on optical properties of Er-Sc silicates prepared from multi-nanolayer films

Polycrystalline Er-Sc silicates (Er(x)Sc(2-x)SiO₅ and Er(x)Sc(2-x)Si₂O₇) were fabricated using multilayer nanostructured films of Er₂O₃/SiO₂/Sc₂O₃ deposited on SiO₂/Si substrates by RF- sputtering and thermal annealing at high temperature. RBS, TEM, GIXD, and PL results show the presence of Er(x)Sc(2-x)SiO₅ with an emission peak at 1528 nm for annealing from 900 to 1100 °C, and Er(x)Sc(2-x)Si₂O₇ with an emission peak at 1537 nm for higher annealing temperature. The PL intensity of the Er(x)Sc(2-x)Si₂O₇ phase is five times stronger than that of the Er(x)Sc(2-x)SiO₅ phase at 1250 °C. From PLE and PL spectra of Er(x)Sc(2-x)Si₂O₇ thin film, we schematically illustrate the Er³⁺ Stark energy levels of ⁴I(13/2) to ⁴I(15/2) manifolds due to the crystal field strength effect of Sc³⁺. Temperature-dependent PL of the Er(x)Sc(2-x)Si₂O₇ phase exhibits a variation of the full-width at half-maximum (FWHM) from 1.1 to 2.3 nm. The narrow FWHM is due to the small ionic radii of Sc³⁺, which enhance the crystal field strength affecting the optical properties of Er³⁺ ions located at the well-defined lattice sites of Sc silicate. A large excitation cross-section (σ(ex)) is equal to 3.0x10⁻²⁰ cm² at λ(ex) = 1527.6 nm.