Optical heating and sensing with plasmonic gold shell and phosphorescent core nanoparticle

Up-converting nanophosphors consisting of Er activator with Yb sensitizer in a NaYF4 matrix have been studied for heating and temperature sensing. We show the response of the nanothermometer to a pump laser operating at 1064 nm with a pulse width of 5-7 nS with a 20 Hz repetition rate. The heating pulse (pump) is probed by the change in the ratio of the two characteristic green emissions centered around 525 and 545 nm. A quasi continuous probe laser operating at 80 MHz and 980 nm is employed to study the effect of the pump laser on the phosphor. The emission is characterized by a spectrophotometer attached to a gated intensifier and a charge coupled device. The time gated measurement shows that the heating produced by 1064 nm pulse is easily resolved with time gating, and the read-out of temperature is deciphered based on the temperature calibration performed with the emission lines. It was found that an increasing the energy of the heating pulse caused a drop in the total green intensity, which had a direct correlation to the increase in the temperature. The signal transduction of the thermal characteristics of the phosphor was delayed in time from the arrival of the heating pulse by about two-three decades in the unit of microseconds. The gold coated phosphor also showed a response to the heating pulse, but the enhancement of both the 525 and 545 nm emissions from the gold shell, to varying extents made the deconvolution of temperature quite involved.