Albert Einstein, Ann. Phys. (Leipzig) 33, 1275 (1910); english translation: "Theory of Opalescence of Homogeneous Liquids and Mixtures of Liquids in the Vicinity of the Critical State", in Colloid Chemistry, J. Alexander, ed. (Rheinhold, New York, 1913), Vol. I, p. 323.
Re: quantised energy being due to Planck.
I'm not so sure about that. I want to say yes and no. Planck employed quantised energy in his equation but it was Einstein that put forward the radical idea of quantising the elecromagnetic radiation field comparing it to a gas. The notion of a light...