Using the transimissivity between two thermal reservoirs and the generalized Planck distributions, we describe the devices that use radiative energy transfer between thermal reservoirs in a unified formalism. Four types of devices are distinguished. For power generators that use the temperature difference between reservoirs, photovoltaic (PV) and thermoradiative (TR) devices respectively use the low temperature photovoltaic cell and high-temperature thermoradiative cell to generate electricity. For active cooling, the electroluminescent (EL) cooling devices apply a forward bias voltage on the object we want to cool, whereas the negative EL cooling devices apply a reverse bias voltage to the heat sink. The relationship among these four devices is explicated. The performance of the negative EL cooling is analyzed, both in the Shockley-Queisser (blackbody spectrum and radiative recombination) framework and the near-field enhancement. The "impedance match" condition derived for PV systems is applied to the negative EL devices. One advantageous feature of the negative EL cooling is that it does not apply the voltage to the target object which we want to cool, and the near-field enhancement can apply to various target materials that support the surface resonant modes. (C) 2018 Elsevier Ltd. All rights reserved.