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Figures (a) and (b) demonstrate that the Pt NPs were successfully modified on the MCNO-based detector after annealing at 750 °C. The Pt NPs had a diameter of 5–10 nm, which is within the typical size range of quantum dots, thus allowing them to be considered as quantum dots. Pt NPs modification of MCNO film resulted in a remarkable ratio of 73, which is approximately 4.1 times higher than the ratio without Pt NPs modification. This excellent result can be attributed to three factors. Firstly, the barrier created between the NPs and the film reduces the dark current by blocking the transport of carriers. Secondly, the plasma resonance effect of the Pt NPs increases the incident light intensity. Lastly, the extinction of the NPs enhances the absorption of incident light and reduces the surface resistance, leading to a high photocurrent enhancement. These results demonstrate that Pt NPs modification plays a critical role in improving the photoproperties of MCNO-based detectors. [Display omitted] • High quality MCNO films had been deposited on Si substrates by RF magnetron sputtering. • High vacuum in situ annealing plays a critical role in the properties of MCNO-based detectors. • High vacuum in situ 750 °C annealing resulted in a 7.61 on/off ratio for MCNO-based detectors. • Pt nanoparticles modification significantly improved on/off ratio of the device to 38.51. The work developed a series of infrared detectors based on the Mn-Co-Ni-O (MCNO) films, which were grown using a radio frequency (RF) magnetron sputtering technique. It was observed that the characteristics of MCNO films were significantly impacted by the annealing temperature. Elevating the in-situ annealing temperature from 550 to 750 °C improved the performances of MCNO films. Additionally, it was found that in situ annealing was more advantageous than ex-situ annealing of 750 °C for the properties of MCNO films. The response value (light to dark) increased from 2.5 to 17.7 at 15 V bias, representing a 6.08-fold enhancement, and the response time decreased to 11.8 ms from 19.9 ms. Furthermore, sputtering Pt nanoparticles on the surface of the MCNO film further improved the I-V characteristics in the dark, resulting in a high on/off ratio of 38.15, which is five times higher than that without the Pt nanoparticles modification. This impressive improvement in photoproperties can be attributed to the Pt nanoparticles/MCNO film barrier, plasma resonance effect generated by the Pt nanoparticles, the extinction of the Pt nanoparticles, and the reduction of surface resistance caused by the Pt nanoparticles. This highlights the potential of metal nanoparticles in the development of infrared detectors. [ABSTRACT FROM AUTHOR]