Difference between 'decided on' and 'decided to'?

Examples:

I have decided on a blue carpet for the bedroom.
I have decided to emigrate to Australia.

What exactly is the difference between "decided on" and "decided to"? Is the usage simply based on construction of the sentence, or do they differ in meaning as well?

Solution 1:

I have decided on + object

I have decided to + verb

The usage is based on the construction of the sentence. You could say:

I have decided to buy a blue carpet for the bedroom.
I have decided on emigrating [or emigration] to Australia.

EDIT

As mentioned in John Lawler's comment, there is a subtle difference between the two. Decide to suggests that you have chosen a plan of action.

I have decided to emigrate to Australia.

I might have been considering staying at home, or I might have been considering other countries, but at any rate, this is what I am going to do.

Decide on suggests that you have chosen one from two or more options that you were weighing.

I have decided on emigration. I am going to Australia. (OR – I have decided to emigrate to Australia.)

I was considering England, Canada and Australia, but I have finally chosen Australia.