You could try an “Add Shader” node instead of a “Mix Shader” node.
Also, it appears you are using a diffuse BSDF output to drive the mix factor. Use an RGB or Value node from the Input category instead. You are forcing a lot of extra calculations instead of just looking up the value/colour.
The noodle dot socket colour indicates the type of data they are passing. Some will automatically do a conversion when joined to another type (yellow rgb dots can be connected directly to grey value dots for example) but as a general rule they should be connected to other sockets of the same colour.