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Plastic scintillators (PS) loaded with neutron sensitive powders to detect special nuclear material without degrading the light yield is well sought. This work reports the synthesis of neutron absorbing gadolinium and boron containing microcrystalline Gd(BO2)3:Tb phosphor and fabrication of composite scintillators by loading the powder in PS. Gd(BO2)3:Tb phosphor (~ 1 µm size) powder prepared through solid-state sintering technique is loaded in polystyrene-based PS which showed increased detection efficiency for neutrons and low energy gammas. A thin film coating method which allows the uniform dispersion of the filled particles in the PS is followed for the preparation of 250 µm thick sheets. 2,5diphenyl oxazole (PPO) and 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP) are added as primary and secondary wavelength shifters in the polystyrene dissolved p-xylene solution. The newly developed composite scintillator is tested using alpha, beta, gamma and neutron radiations for the scintillation efficiency. Three different weight percentage Gd(BO2)3:Tb loaded PS are studied for their response towards different radiations to optimize the filling. The newly developed thin PS sheet exhibits 2 times enhancement in the radioluminescence emission compared to unloaded PS. Pulse height spectra are acquired and analysed for different types of radiation. The neutron response is studied for moderated and unmoderated configurations of the Am-Be neutron source.