A radiation detector can include a solid organic/plastic scintillator that enables neutron and gamma interactions to be readily distinguished via pulse-shape discrimination. Embodiments make use of a scintillator including a polymer matrix with a dispersed scintillation material exhibiting thermally activated delayed fluorescence. The scintillation material can include an organic luminescent material that is free of heavy metals and in which excited triplet states are efficiently promoted into excited singlet states by thermal energy, the excited singlet states then generating a delayed fluorescence when decaying to ground state. As a result, the scintillation material, when exposed to ionizing radiation, can produce a combination of prompt and delayed fluorescence sufficient to enable neutron and gamma interactions to be readily distinguished via pulse-shape discrimination techniques.