I copied this video tutorial.
Between your Emission node and material output, add a Mix Shader node. Plug the Emission output to the first Mix's shader input, and add a Transparent BSDF node plugged in the Mix's second input.
You can play with the Mix's factor value to change how much you mix the Emission with the Transparent BSDF shader. 0 is fully Emission shader, 1 is fully Transparent BSDF shader.