Ultra-Small YPO4-YAG:Ce Composite Nanophosphors with a Photoluminescence Quantum Yield Exceeding 50%

Synthesis of high quality colloidal Cerium(III) doped yttrium aluminum garnet (Y₃Al₅O₁₂:Ce³⁺, “YAG:Ce”) nanoparticles (NPs) meeting simultaneously both ultra-small size and high photoluminescence (PL) performance is challenging, as generally a particle size/PL trade-off has been observed for this type of nanomaterials. The glycothermal route is capable to yield ultra-fine crystalline colloidal YAG:Ce nanoparticles with a particle size as small as 10 nm but with quantum yield (QY) no more than 20%. In this paper, the first ultra-small YPO₄-YAG:Ce nanocomposite phosphor particles having an exceptional QY-to-size performance with an QY up to 53% while maintaining the particle size ≈10 nm is reported. The NPs are produced via a phosphoric acid- and extra yttrium acetate-assisted glycothermal synthesis route. Localization of phosphate and extra yttrium entities with respect to cerium centers in the YAG host has been determined by fine structural analysis techniques such as X-ray diffration (XRD), solid state nuclear magnetic resonance (NMR), and high resolution scanning transmission electron microscopy (HR-STEM), and shows distinct YPO₄ and YAG phases. Finally, a correlation between the additive-induced physico-chemical environment change around cerium centers and the increasing PL performance has been suggested based on electron paramagnetic resonance (EPR), X-ray photoelectron spectrometry (XPS) data, and crystallographic simulation studies.     

Conditions for Crystallization of LAS Glass-Ceramics as a Function of Nucleating Agent Amount and Heat Treatment

The effect of nucleating agent content and of the crystallization heat treatment have been explored on a commercial lithium-aluminosilicate (LAS) composition (Eurokera Kerablack). Using X-ray diffraction (XRD) on treated samples and differential scanning calorimetry (DSC), we have observed that crystallization occurs differently in nucleating agent-depleted materials than in standard LAS. In particular, we found larger grain size and β-spodumene content than in KeraBlack. We also assessed the decisive effect of the heating rate: although nucleation can take place under almost arbitrary conditions (except with no nucleating agent), the final materials depend on the crystallization cycle applied. They contain more β-quartz with smaller grain size if the cycles and the soak treatments are short; they consist mainly of β-spodumene with large grains if the ramps and soak times are long. We also observed that a soak heat treatment does not influence the crystallization in the case of low content of nucleating agents, but can be used to obtain crystallization if only ZrO₂ is added. The impact of nucleating agents underlines the importance of heterogeneous nucleation in these glass-ceramics. We conclude that it is not possible to create a fine-grained LAS glass-ceramic without the proper amount of nucleating agents.     

Introduction to the 3GPP-defined NTN standard: A comprehensive view on the 3GPP work on NTN

With the recent publication of a set of technical specifications in 3rd Generation Partnership Project (3GPP) related to non-terrestrial network (NTN) enhancements, a global standard for satellite systems is newly defined aiming to support any orbit, any frequency band, and any device. It opens the door for the seamless integration of satellite network component in 5G system and beyond, delivering the promise of a ubiquitous mobile system that can support new use cases. The emergence of hybrid terrestrial-satellite systems is the result of a joint effort between stakeholders of both mobile and satellite industries and is paving the way to new business opportunities. This paper attempts to provide a comprehensive view on this 3GPP NTN standard and what are the next steps.