# Breakthrough in Luminescence ThermometrySupersensitive Emission Line Shift of Whispering Gallery Modes in Rhodamine B‑Doped Cellulose Fiber Microresonators

## TL;DR

A new cellulose fiber doped with Rhodamine B shows exceptional temperature sensitivity through light emission shifts, making it a promising material for optical thermometers.

## Contribution

The first demonstration of supersensitive temperature sensing using WGM emission shifts in Rhodamine B-doped cellulose microfibers.

## Key findings

- Rhodamine B-doped cellulose fibers exhibit a spectral shift of ∼0.47 nm K–1 due to temperature changes.
- The observed blue shift is 27 times more sensitive than other microresonators.
- The method achieves a temperature resolution of ≈0.17 K.

## Abstract

The development of optically active materials enabling
rapid, precise,
and accurate remote detection of physical parameters is crucial for
advancing science and modern technology. In this work, we investigate
resonant effects and light propagation in cellulose fibers doped with
Rhodamine B for optical thermometry applications. These fibers were
successfully produced by using the spinning method with N-methylmorpholine N-oxide. Their optical properties were investigated
through absorption and emission spectroscopy, confirming the integration
of Rhodamine B into the cellulose matrix. Notably, the cylindrical
shape of the modified fibers significantly affects the emission spectra
when excited at the fiber edge, revealing sharp and superimposed whispering
gallery modes (WGMs). A confocal system with a 532 nm laser was used
to analyze for the first time the WGM emission from the optically
active cellulose microfibers. The WGMs displayed high susceptibility
to the negative thermo-optical coefficient of the resonating cavity,
leading to a giant spectral shift. This unprecedented temperature-induced
blue shift of the WGMs provides the highest reported sensitivity-27
times higher than other microresonatorsdemonstrating a spectral
shift of ∼0.47 nm K–1. With excellent temperature
resolution (≈0.17 K), our findings highlight the great potential
of this method and material as a supersensitive optical thermometer.