[en] The method for improving sensitivity and simultaneous determining terbium, praseodymium and europium in gallium oxide, gallium-yttrium garnet mixture, gallium salts and other compounds of high purity in the content range of rare earths from 2x10^-2 to 1x10^-5 mass.%. Thus, gallium, yttrium and rare earths determined compounds are mixed in the following component ratios in crystallophosphor, mass.% : yttrium oxide 34-50, terbmium oxide 0.0001-0.02, praseodymium oxide 0.00001-0.02, europium oxide 0.00001-0.02, gallium oxide - the rest. The mixture obtained is calculated at 1350-1400 deg C during 30-40 min, deriving mixed element oxides, and then luminescence intensity is indicated