Optical fibre thermometry using ratiometric green emission of an upconverting nanoparticle-polydimethylsiloxane composite

•Upconverting nanoparticles-PDMS composite explored as temperature sensing material.•Dip coated on optical fibre to realize simple & portable thermometer probe.•Shows an excellent linear temperature response in 295 K-493 K region.•Maximum synthesis temperature needed can be achieved with laboratory hot plate.•Better alternative to Er3+ doped glass thermometer in terms of low temp. fabrication.