Well, it's more to do with the temperature rather than anything. The lattice idea is a simplification of what's actually going on. It's used to explain why continuous spectrums are generated by materials even though on an atomic scale they can only actually emit certain wavelengths. I'd love to know how it works in a liquid but that's the way I was taught. Presumably it works in a similar way for liquids (such that the emitted wavelengths represent an average heat and so on). On the internet there doesn't actually seem to be any explanation as to what's going on, the closest it gets to is Planck's derivation of black body laws - by treating particles as perfect oscillators. A common theme in physics at this scale but it doesn't help laser lovers who might be talking about it 80 years later.