Thermoluminescence (TL) response of newly synthetic silicon-activated Ca9AlP7O28 nanophosphor doped with different concentrations (0.3–10 mol%) (abbreviated as CAP: Six) were prepared by the sol–gel method. The optimum concentration of Si ions for the best TL response was found to be 0.3 mol% (CAP: Si0.3), which was selected for subsequent dosimetric measurements. Phase purity and the crystal structure of the CAP: Si0.3 sample were identified and verified using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis, where results obtained confirmed the successful synthetic method used in the preparation of the nanophosphor samples. Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) mapping revealed the localization of constituent elements and indicated the homogeneous distribution of Si-ions as well as the feasibility of dopants in the herein sample. The dosimetric properties of the CAP: Si0.3 sample, including glow curve structure, reproducibility, repeatability, dose–response and fading effect, were extensively investigated. The gamma irradiated CAP: Si0.3 sample exhibited a simple glow curve of a single prominent peak centred at 222 ± 1.33°C with considerably high TL intensity (1.22 relative to MTS-700 TLD detector). The relative standard deviation (RSD) of peak areas of CAP: Si0.3 were 5.25 and 2.7% for reproducibility and repeatability studies, respectively. These values of RSD were <10%, so they were acceptable internationally. A good linear dose–response relationship was achieved over a dose range of up to 20 Gy with an excellent correlation coefficient of R2 = 0.9969 and a calibration factor of F = 51.75 × 107 a.u./Gy. Almost no fading was registered from the studied CAP: Si0.3 sample after irradiation. Zeff values were found to be in the range 11.62 to 11.61, which are closely related to that of natural bone (11.3 to 11.8). Minimum detectable dose of CAP: Si0.3 had a value of 11 μGy. The outstanding features of this herein-prepared sample make it a good TLD nanophosphor, very suitable for personnel and environmental dosimetry of γ-radiation within the studied dose range. [ABSTRACT FROM AUTHOR]