A non-intrusive optical method to measure gas phase temperature in strongly scattering multiphase environments under high-flux, broad-band irradiation, relevant to conditions in high temperature solar reactors was developed and demonstrated. The high-flux irradiation with a peak flux of 450 kW/m(2) was provided by a 6 kW metal-halide lamp coupled with a reflector and two concentrators. An ethylene/air diffusion flame, which contains fine soot particles, was employed to provide a high temperature reacting flow (approximately 1800 K) with strong optical interference from nano particles having a peak soot volume fractions of similar to 16 ppm (with irradiation) under conditions of relevance to solar reactors. Under this environment, the proposed laser-based thermometry technique, line-wise two-line atomic fluorescence (TLAF) has been successfully demonstrated to measure flame temperature with good spatial resolution of similar to 1 mm. It was found that the measurement accuracy in the presence of particle and the high-flux external radiation is 65 K at a typical flame temperature of similar to 1800 K, while the measurement precision is 38 K. Results reveal that the presence of high-flux irradiation increases the flame temperature by typically 50-100 K. This paper presents a thermometry technique that is suitable for temperature measurement within solar reactors, particularly in hybrid solar-thermal receiver-combustor systems. The experimental setup, measurement methodology and data processing are discussed, followed by the temperature measurements. (C) 2017 Elsevier Ltd. All rights reserved.