(Dis)Order and Luminescence in Silicon-Rich (Si,P)–N Network Sr₅Si₇P₂N₁₆:Eu²⁺

Abstract

In this work, we present the synthesis, characterization, and optical properties of Sr 5 Si 7 P 2 N 16 :Eu 2+ , the first tetrahedral (Si,P)−N network in which Si occupies more than 50% of the tetrahedra. While past studies have shown progress with anionic (Si,P)−N networks, the potential of silicon-rich compounds remains untapped. The synthesized compound Sr 5 Si 7 P 2 N 16 exhibits a unique mixture of substitutional order and positional disorder within its network. The analytical challenges posed by the similarities between Si 4+ and P 5+ , along with the network's disorder, were overcome by combining single-crystal X-ray diffraction and scanning transmission electron microscopy EDX mapping. Low-cost crystallographic calculations provided additional insights into the identification of tetrahedral occupations in mixed networks. Luminescence investigations on Sr 5 Si 7 P 2 N 16 :Eu 2+ revealed yellow emission, adding to the known blue, green, and orange emission maxima of Sr−(Si,P)−N networks, highlighting the variability of such compounds.

The Fundamental Disorder Unit in (Si, P)−(O, N) Networks

“…In this context, we also added new 31 P NMR data on literature known Sr 2 SiP 2 N 6 and Sr 5 Si 7 P 2 N 16 as reference for ordered (Si, P) networks. [7,8] LCC were used to confirm our results and provide insight into Sr 16 Si 9 P 9 O 7 N 33 where no NMR data were available. As an impetus for future research, we briefly investigated the optical properties of the SiPONs when doped with Eu 2 + .…”

“…Typically, total deviations below 3 % indicate a congruent model. [7] The comparison and evaluation of all five methods for the four compounds Sr 3 SiP 3 O 2 N 7 (1), Sr 5 Si 2 P 6 N 16 (2), Sr 5 Si 2 P 4 ON 12 (3), and Sr 16 Si 9 P 9 O 7 N 33 (4), are shown in Figure 5, where columns 1-5 represent each method, column 6 the total percentage deviation, rows 1-4 the respective compounds and the bottom row the reference data of pure nitridosilicates and nitridophosphates. Each cell shows a stack of all (Si, P) Wyckoff positions with their calculated values, their overall average, and their expected value.…”

Super-Tunable LaSi3N5 Structure Type: Insights into the Structure and Luminescence of SrSi2PN5:Eu2+

“…By using a combination of analytical techniques, including single-crystal and powder X-ray diffraction as well as 31 P solid-state NMR and powder neutron diffraction, we were able to elucidate its complex network. After Sr 5 Si 7 P 2 N 16 , SrSi 2 PN 5 is the second silicon-rich, but this time, fully ordered (Si,P)–N network . The challenges posed by the chemical similarity and low X-ray contrast between the key elements were effectively addressed, highlighting the importance of methodological diversity in material characterization.…”

“…Since the investigation and differentiation of these elements by X-ray diffraction are often considered insufficient, it must be complemented by other analytical methods. In a previous work, we have already proposed different approaches to distinguish Si 4+ and P 5+ , e.g., by exploiting their characteristic X-ray emissions in scanning transmission electron microscopy in combination with energy-dispersive X-ray spectroscopy at atomic resolution, better known as scanning transmission electron microscopy energy-dispersive X-ray (STEM-EDX) maps. , However, their discrimination is not limited to the interaction with their electron clouds, as we have shown by studying the 31 P solid-state NMR spectra of disordered oxonitridosilicate phosphates (SiPONs), Sr 3 SiP 3 O 2 N 7 and Sr 5 Si 2 P 4 ON 12 . While these methods provide reliable results, in this work, we were interested in further extending the analytical capabilities for this class of compounds by powder neutron diffraction (PND) and adding another method that interacts with the nuclei.…”

The Fundamental Disorder Unit in (Si, P)−(O, N) Networks

“…Furthermore, we have previously shown that the elucidation of the structure and in particular the network in (Si, P) compounds is a multi-step process that often utilizes high-level analytics, such as atomic-scale scanning transmission electron microscopy (STEM). [7,8] However, we are interested in making this workflow more accessible by extending the analytical scope to more common methods, such as NMR. In this contribution, we present Sr 3 SiP 3 O 2 N 7 , Sr 5 Si 2 P 4 ON 12 and Sr 16 Si 9 P 9 O 7 N 33 as the first alkaline earth SiPONs.…”