## 1 Introduction  
GaN-based light-emitting diodes (LEDs) have been widely used for industrial lighting and outstanding backlight in liquid crystal displays and have become an increasingly important technology [1; 2; 3]. In particular, tunable white-light engines (changing color temperature), high-quality display, and tunable color lighting (changing color) have attracted intense interest [4]. Generally, LEDs are tuned by adjusting the injection currents of the different color LEDs. In addition, the driving current, and thus the light output power (LOP), can also be changed to obtain higher current density and light intensity. However, changing the current will lead to a change in the junction temperature (\(T_{j}\)) and emission peak wavelength [5], and the \(T_{j}\) itself is also a key factor influencing the LED emission peak [6]. For some use in manufacturing applications, LED lighting must be able to function in extreme ambient conditions, such as a high-temperature environment (furnace lighting) and freezing environment (hyperborean lighting). In the future, LED may be used in the much lower temperature, such as aerospace engineering. To fabricate a LED module with better color quality or better color coordinates, or with application in extreme temperature range, it is necessary to understand the electroluminescence mechanism in LEDs under wide range of the \(T_{j}\) and the injection current.  
Investigation of photoluminescence (PL) and electroluminescence (EL) properties of InGaN LED in the low temperature attracted lots of research for years because it is necessary for better understanding of the mechanism of the luminescence. [PERSON] et al. had used the PL to study the dynamics of photoexcited excitons in InGaN/GaN with different indium compositions in the temperature range of 10-300 K [7]. [PERSON] et al. had measured the PL properties in the temperature range of 6-300 K, and found the temperature dependences of the peak energy and linewidth are induced by the localized carrier hopping and thermalization process [8]. PL was used by [PERSON] et al. to calculate the spontaneous emission quantum efficiency (QE) of blue, green, and red LED from temperature 77 K to 800 K [9]. However, there are few reports about the EL properties of InGaN/GaN LEDs in the low temperature (below 220 K) because \(T_{j}\) is hard to determine. Generally, it is difficult to determine \(T_{j}\) with high current injection for temperatures under 213 K due to the self-heating of the LED, and it is also difficult to perform EL measurements at such low temperatures. [PERSON] et al. used a highly spectrally and spatially resolved scanning electroluminescence microscopy to trace detailed spectra of an InGaN/GaN LED at 300 K [10]. [PERSON] et al. have measured the spectra of the LEDs at 4.2 and 77 K, rather than in a continuous range of low temperatures [11].  
In this work, we investigated the electroluminescence (EL) properties of blue and green GaN-based LEDs in the temperature range of 120-373 K, using specially designed LEDs with a built-in \(T_{j}\) sensor unit. To the best of our knowledge, this work is the first detailed report of the changes of the EL spectra with changes in \(T_{j}\) and current. We investigated the mechanisms of the LED peak energy changes, and in particular the effect of the injection current and \(T_{j}\) on the emission peak energy. It was found that the EL and electrical properties of blue LED are different from those of green LED, and the origins of these differences are elucidated and described in detail.