YAG:Ce, a widely employed phosphor for LED wavelength conversion applications, comes in different forms, including polycrystal (powder), single crystal, and composite single crystal varieties. We investigated Epoch Neo^TM, a composite single crystal incorporating Al₂O₃ as a heat distribution and optical guiding material embedded within its luminescent core. The properties of Epoch Neo were analyzed and compared with those of its polycrystal counterparts in this paper. Multiple characterization techniques like chromaticity points, color temperature, phosphor temperature, and speckle pattern were employed to study the effect of variable laser input power on both polycrystal powder and composite single crystal of YAG:Ce. It was found that under the influence of pumping blue laser high input optical power the composite single crystal phosphor’s performance was significantly better compared to that of the polycrystal.

In this study, we experimentally demonstrate that the magnetic properties of nitrogen-doped graphene (NG) are influenced by the configuration of nitrogen dopants, namely graphitic, pyridinic, and pyrrolic, along with the overall nitrogen concentration. The NG materials were prepared via a two-step thermal treatment process. The first step involved heating in ammonia at 400 °C, followed by a second post-annealing step at 600 °C. Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy (SEM–EDS) analysis performed at 25 μm resolution confirmed uniform elemental distribution across the samples. X-ray photoelectron spectroscopy (XPS) revealed that while the total nitrogen content decreased from 11.9 at.% in NG to 5.5 at.% in the post-annealed sample, the ratio of graphitic to pyrrolic nitrogen increased from 0.4% to 3.8% and the ratio of graphitic to pyridinic nitrogen increased from 0.8% to 2.5%. Raman spectroscopy confirmed the presence of prominent D and G bands at ~1352 cm⁻¹ and ~1589 cm⁻¹, respectively, along with a 2D band at ~2692 cm⁻¹, indicating the presence of few-layered graphene and defect-related features. The ${\displaystyle \frac{{\mathrm{I}}_{\mathrm{D}}}{{\mathrm{I}}_{\mathrm{G}}}}$ ratio increased from 1.12 to 1.27 in the post-annealed sample, indicating increased disorder after annealing. Magnetic characterization showed a marked enhancement in the magnetic properties with increased graphitic nitrogen content. The saturation magnetization (M_s) reached 0.13 emu g⁻¹, ~42% higher than that of the material heated in ammonia, with the coercivity increasing from 40 Oe to 750 Oe. These results emphasize the pivotal role of nitrogen configuration in the graphene host, specifically the promotion of graphitic nitrogen species, in tailoring the ferromagnetic response of NG.

Illumination sources based on phosphors, pumped by laser diodes (LDs), have seen rapid developments over the past decade. Here, we present a new, to the best of our knowledge, design that features both spectral richness and the capability for high brightness. Complete design details and operational characterization have been described. This basic design can be extended in various ways to customize such lamps for different operational requirements. A hybrid arrangement of both LEDs and an LD is used to excite a mixture of two phosphors. The LEDs, in addition, provide a blue fill-in to enrich output radiation and to tune the chromaticity point inside the white region. The LD power, on the other hand, can be scaled up to generate very high brightness levels that are not achievable with pump-ing from LEDs alone. This capability is gained using a special transparent ceramic disk that carries the remote phos-phor film. We also show that the radiation from our lamp is free from speckle-producing coherence. (c) 2023 Optica Publishing Group