Natural diamonds of IIa type were studied by the methods of dc photoconduct
ivity and microwave photoconductivity. Their optical absorption spectra und
er normal conditions and the low-pressure (approximate to 10(-5) Pa) photoe
mission were measured. The microwave conductivity of diamond (having the ne
gative surface electron affinity) was treated in terms of a model including
both internal and external photoelectric effects. (C) 2000 MAIK "Nauka/Int
erperiodica".