Emissive – You need to assign a texture to the emissive layer (could be a small solid color layer if you don’t need any texture) .
Emissive materials do not affect the surrounding objects , they affect the material , a good example is a Screen, that has its own brightness, you can see the Screen and Laptop from the 3D library as a sample. 
Reflection – Stardust has planar reflection and Env reflection , so if you have a setup with planar reflection you could see the particles in the reflection , the Environment is a pre-rendered / HDRI frame, that does not include the current particles / Models .