Transparent Ce:Lu3Al5O12 (Ce:LuAG) phosphor ceramics are promising for high-power white lighting due to their high quantum efficiency, thermal stability and low thermal quenching. However, the shortage of red spectral composition and expensive price are preventing the application of Ce:LuAG phosphor ceramics in high-quality white lighting. In this work, (Lu,Gd)3Al5O12-Al2O3 (LuGAG-Al2O3) nanoceramics were prepared by partially replacing Lu3+ with Gd3+ through glass crystallization. These ceramics exhibit outstanding transparency and excellent mechanical properties. Compared with Ce:LuAG-Al2O3 transparent nanoceramics, the emission spectrum of transparent Ce:LuGAG-Al2O3 nanoceramics shows a substantial red shift (505 nm→570 nm), which effectively supplement the red light lacking in Ce:LuAG ceramics. With a maximum quantum efficiency of 81.4% and excellent thermal stability (87.6% @423 K), these nanoceramics have potential for high-power white lighting. When used in high-power LED and LD lighting, Ce:LuGAG-Al2O3 transparent nanoceramics achieve continuous adjustable changes from green light to orange-yellow light, and furthermore provide high quality warm white lighting with low color temperature, high color rendering index, and excellent luminous efficiency. Combining the facile and moderate elaboration process through full glass crystallization, the transparent Ce:LuGAG-Al2O3 nanoceramics reported in this paper are therefore regarded as promising color converters candidates for high-power warm white LED/LD lighting.

Temperature (T) is a key parameter controlling the rheology of lava flows. Since hazardous behavior of eruptions prevents direct measurements of hot magmatic bodies [1], the temperature is mostly retrieved by measuring the infrared (IR) radiance of the lava flow [2, 3]. The determination of T is however subjected to important errors related to the poor knowledge of one of the most critical parameters, namely spectral emissivity (ε). In this study, we explored the temperature–emissivity relationship for basaltic magmas, mostly from the 2014–2015 Holuhraun eruption. We performed in situ spectral emissivity measurements at relevant magmatic temperatures (from room temperature up to 1800 K) over a wide spectral range (400–8000 cm−1) covering TIR, MIR and SWIR regions, using a non-contact IR emissivity apparatus [4]. To unravel the complex radiative behavior of basalts with temperature evolution, structural, chemical and textural analyses (SEM, EMPA, Raman spectroscopy, DSC, XRD, and TEM) were systematically performed. Our results show that spectral emissivity varies accordingly with temperature, wavenumber, and is greatly affected by micro-scale crystallization, emphasizing the effect of small change in silicate structure on magma radiative properties. Because of the multiphase nature of lava, each constitutive phase (glass, melt, crystal, vesicles) contribute differently to the spectral emissivity. The evaluation and quantification of the impact of these phases on effective thermal radiative properties is a key point to improve the accuracy of lava T determination. These new data will ultimately improve our knowledge of the complex lava flow properties that are crucial in thermo-rheological models for hazard assessment [5]. References: [1] Kolzenburg et al. 2017. Bull. Volc. 79:45. [2] Harris, A. 2013: Cambridge University press. 728. [3] Rogic et al. 2019 Remote Sens., 11, 662 [4] De Sousa Meneses et al. 2015. Infrared Physics & Technology 69. [5] Thompson and Ramsey, 2021, Bulletin of Volcanology, 83:41. Keywords: Spectral emissivity, temperature, IR spectroscopy, rheology, basalt