direct and indirect band gap material

[prasad vs sarma]

Now i know what is direct or indirect band gap material, but How can we determine a material has direct or indirect band gap, experimentally?:roll:

 

[ahsan_i_h]

Lets make a pn junction from the material, and make it forward biased. Now measure the frequency of the electromagnetic wave radiated from the junction. If it is direct band gap material then the frequency of the radiated wave should match with the frequency found from E=hu(planks equation) when we put the forward voltage drop(as electron volt) in the left side of the equation.
I just gave an idea.