Create smooth vertical gradient with Emission shader and Diffuse shader I am a absolute blender beginner. Today I created my first scene which was exactly what I wanted to achieve, but then I Ctrl+A to re-scale everything and added a particle system an boooom my perfect material didn't work after anymore. I am so desperate right now because I spent hours and hours to recreate what I have done before but it will not appear like before, although it was really "simple" :-) Pleeeease please help me to recreate my scene. This is what it looked like today in the morning (with me in the reflection sorry):

I made this scene by building simple mountains like in this tutorial.


Material of the mountain-plain = green Diffuse BSDF.
Right above the camera an Area lamp with size 16.000 and Strength 4000.00
World Setting: Volumne Scatter with a light blue color and Density 0.008
The moon (UV-Sphere) with an Emission Shader white color and Strength 1.100


For every single mountain I selected the faces, created a material and assigned it. For these materials I used the nodes as seen in this screenshot (this is what I tried to recreate): 

What I am not sure of are the settings of the above black&amp;white ColorRamp I think I used the Fresnel Node instead!? Important was, that in the color ColorRamp I used the same start color as I used for the mountain plain to achieve (so I thought) a smooth transition. It will not work out like before - I get hard color edges, not as much glowing as in the picture from earlier today.. 
Thanks for any help !!
Better method would be to use Separate XYZ node as a factor between Diffuse/Emission shader.

It basically take Z height of your mesh and assign material based on it.

You can control factor by Color Ramp node.



Edit:

First of all, issue is from Mapping Node. You need to switch it to Point, set Scale to 1, 1, 1, and lower Z Location value. This will be our 'starting' position. Also set Color Ramp to default state (black to the left, white to the right):



Now if you want to control gradient falloff we will use the simplest (I think) method for it by changing only Scale and Location Z values in Mapping Node.

Scale Z value will control gradient falloff - lower value smoother gradient.

Location Z value will move it up and down. 

Look at some of these examples (Location Z and Scale Z noted on pictures):



And going further if you want smooth falloff (top left corner) and hard emission on top of it, you can move white value in Color Ramp node to the left a bit to tweak it.

Blend file:

Here are some of the examples, and little extra fun with Color Ramp node.