Electron-beam pumped AlGaN lasers are interesting candidates to overcome the technical issues in the development of deep UV laser diodes [1]. However, an improvement of the device design and deeper understanding of the physical processes involved are necessary for the implementation of devices that operate at room temperature. In this presentation, we analyze the optical properties of AlGaN-based separate confinement heterostructures (SCHs) designed for electron beam pumped lasing at 355 nm. We study their photoluminescence under various injection levels and compare the internal quantum efficiency of the spontaneous emission and the lasing threshold power density to determine the limiting factors. At room temperature, carrier localization in the quantum wells leads to an enhancement of the radiative efficiency. However, our results show that the lasing threshold is more sensitive to the injection efficiency than to the radiative efficiency. Therefore, designs including graded alloys (graded index separate confinement heterostructures, GRINSCH [3]) can result in a reduction of the lasing threshold, in spite of their lower internal quantum efficiency. [1] S. Cuesta et al., J. Phys. D: Appl. Phys. (2022). DOI: 10.1088/1361-6463/ac6237 [2] S. Cuesta et al., Appl. Phys Lett. 119, 151103 (2021) [3] S. Cuesta et al., Optics Express 29, 13084 (2021)