SNR-enhanced temperature-insensitive microfiber humidity sensor based on upconversion nanoparticles and cellulose liquid crystal coating

Combining upconversion nanoparticles (UCNPs) and cellulose liquid crystal (CLC) film, a microfiber relative humidity (RH) sensor with enhanced signal-to-noise ratio (SNR) is proposed. The sensor head consist of a microfiber successively coated with a UCNP fluorescent layer and a hydrophilic CLC film layer. The UCNP fluorescence spectra is located in the photonic band gap of the CLC film, resulting in mirrorless low threshold lasing emission. The addition of the CLC film enhances the SNR by 12 dB. The RH response and the temperatureinsensitivity are both experimentally verified. The sensitivity of the proposed sensor is 284.75 pm/%RH. It is a promising structure for highly sensitive and accurate RH monitoring.