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This paper reports the characterization of two scintillating materials in powder form, Gadox and YVO embedded in a light-activated resin, used in a probe developed for oncological brachytherapy in-vivo dosimetry. The materials were characterized in terms of internal absorption, scintillation decay time, and light yield. The measurement of the optical characteristics highlighted a significant internal absorption at the scintillation light wavelength, with values of 6.5 dB/mm for Gadox and 14.1 dB/mm for YVO. Measurements of the characteristics scintillation time and of the light yield were performed with a novel method based on single photon counting, profiting from the long decay time of the materials under study. Measurements have been complemented by a two-step simulation with Geant4 to study the energy deposition followed by a ZEMAX OpticStudio® ray tracing to estimate the light collection efficiency. The decay time for scintillating materials were measured to be τ G a d o x = (458 ± 3 ± 3) μ s and τ Y V O = (451 ± 8 ± 3) μ s and the estimated values of the light yield are (7.1 ± 0.5) × 104 photon/MeV for Gadox and (4.8 ± 0.5) × 104 photon/MeV for YVO. [ABSTRACT FROM AUTHOR]