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For optical nanothermometers, it is difficult to improve the absolute sensitivity (SA) and relative sensitivity (SR) at the same time. In this paper, a new strategy is explored to improve the SA and SR of nanothermometers based on upconversion (UC) nanorods (NaYF4:Yb3+/Er3+/Nd3+/Gd3+). With the temperature increasing, the intensity of UC luminescence bands of Er3+ decreases, and that of the 4S3/2 → 4I15/2 (Er3+) drops the most. Meanwhile, the intensity of infrared UC luminescence bands of Nd3+ increases, and that of 4F3/2 → 4I9/2 (Nd3+) increases the most. A new luminescence intensity ratio (LIR) strategy is used, which is based on two luminescence intensities that show the strongest opposite change with the temperature. The SA and SR of different LIRs are compared. It is found that the LIR (4S3/2 → 4I15/2/4F3/2 → 4I9/2) can significantly increase SA and SR. The values of SA and SR in 303–573 K are in the range of 0.003–0.226 K–1 and 1.09–2.37 %K–1, respectively. This work provides new strategies for improving temperature sensitivity.

Single-photon avalanche diodes (SPADs) are widely used for weak light detection due to their high gain and high sensitivity. Unfortunately, SPAD devices have random telegraph signal (RTS) noise during the avalanche transition phase, which makes circuit design more difficult. Therefore, the modeling of RTS noise in SPAD devices is of great significance for the design of signal processing circuits. However, RTS noise is not included in the traditional equivalent circuit model. In response to the above problems, this paper implements an equivalent circuit model with RTS noise based on the Cadence. The model is built based on the basic components in the library, and it has strong application universality. The model is validated in a novel embedded photogate SPAD device (EP-SPAD). It accurately simulates the RTS noise and IV characteristics of the EP-SPAD device. In addition, the threshold voltage of EP-SPAD device operating in Geiger mode is precisely defined based on the characteristics of RTS noise. When the reverse bias voltage is increased from 0 V to 15 V, the IV characteristics of the model are consistent with the EP-SPAD device.