We have developed a simple, low-cost and highly efficient optical temperature sensor based on intensity ratio of down-conversion green fluorescence of Er3+ ions doped in SrGdGa3O7 single crystal. The sensor consists simply of a 384 nm light emitting diode, two narrow-band interference filters, two Si-photocells and two multimeters, without use of a monochromator or spectrometer or focusing lens. It has a simple, compact structure and is Ipw-cost. The experimental results show that the device displays highly efficient sensing performance with good signal-to-noise ratio and high thermal resolution and temperature sensitivity, which has a value of (5.5-102.1) x 10(-3)K(-1) in the considered temperature range of 100-430 K. In addition, the experiments were repeated using a spectrometer and consistent results are obtained. (C) 2017 Elsevier Ltd. All rights reserved.