Here we have developed a series of SWIR-emitting materials with high luminescence efficiency and excellent thermal stability by co-doping Cr3+-Yb3+ ion pairs into Lu0.2Sc0.8BO3 host materials. However, the lack of ideal blue-pumped short-wave infrared (SWIR) phosphors with an emission peak longer than 900 nm greatly limits the development of SWIR LEDs using light converter technology. The ability of phosphors to absorb blue light from commercial LED and convert the excitation energy into long-wavelength infrared luminescence is crucial for the design of cost-effective and high-performance phosphor-converted infrared LEDs. The growing demand for spectroscopy applications in the areas of agriculture, retail and healthcare has led to extensive research on infrared light sources. The model is experimentally corroborated with cerium‐doped yttrium aluminum garnet slabs. The study is based on an analytical development which calculates the extraction efficiency and the brightness of an additional face for any refractive index and any propagation loss inside the medium. This article tackles the extraction of light emitted inside a rectangular luminescent slab by an additional face. Balancing the extraction efficiency and the brightness, a 1 × 3 × 22 mm3 Ce:YAG slab with an optimized edge face and with mirrors on the lateral faces exhibits an efficiency 1.9 times better and a brightness 5.6 higher than a Ce:YAG in a standard configuration. Therefore, the output brightness can be easily improved and controlled by the dimension of the additional face. Results highlight that the extraction efficiency by an additional face can be improved even if the area of the additional face is lower than the area of the smallest face of the slab, generally chosen as the output face in a standard configuration. The model gives an analytical expression of the extraction efficiency and the brightness of the additional face as a function of the slab parameters (dimensions, refractive index, losses). The study is based on a fully analytical approach corroborated experimentally with cerium‐doped yttrium aluminum garnet (Ce:YAG) slabs. This work explains how an additional face breaking the rectangular symmetry can improve the extraction efficiency and brightness. The extraction efficiency and the brightness are critical parameters to increase the performance of luminescent rectangular slabs such as scintillators, luminescent concentrators, or diamonds with NV centers. According to the results of the experiments, the accuracy of the classification of snow, wet and water can reach 97 %, while the accuracy of the dry and wet road surface conditions is respectively 73 % and 68 %. Finally, the NIR LED system with the LED sources at 970, 14 nm is experimentally tested and validated with an incident angle from 78.7 to 86.2∘. In addition, the effect of the spectral bandwidth of the LED sources on the system performance is theoretically studied. For this, the appropriate wavelengths of the LED tri-wavelength source are first computed from experimental data taking into account the specific LED spectral shape. Considering these advantages, the feasibility of the LED system to recognize road surface conditions is investigated. They are less sensitive to temperature and have lower costs. This choice is based on the advantages of LED sources over laser diodes. The objective of this paper is to propose and develop a new system with three near-infrared (NIR) LED sources. Currently, the existing investigations to detect road surface conditions still have limitations in daytime and nighttime conditions. The driving safety of autonomous vehicles will strongly depend on their ability to recognize road surface conditions such as dry, wet, snowy and icy road.
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