Power dependent photoacoustic and photoluminescence studies on a Ho/Yb doped YO phosphor.

The Ho/Yb doped YO phosphor samples were synthesized through a combustion method and then were annealed at 800 °C, 1000 °C, and 1200 °C. The cubic phase of the synthesized samples was confirmed by XRD analysis. The upconversion (UC) & photoacoustic (PA) spectroscopic studies were done on prepared samples and both spectra are compared. The samples have shown intense green upconversion emission at 551 nm due to the S → I transition of Ho ion along with other bands. The maximum emission intensity is obtained for the sample annealed at 1000 °C for 2 hours. The authors have also measured the lifetime corresponding to S → I transition and found that lifetime values follow the trend of upconversion intensity. The maximum lifetime of 224 μs is observed for the sample annealed at 1000 °C. A photoacoustic cell & a pre-amplifier was fabricated and optimized for maximum sensitivity of the system. The PA signal was found to increase with increase of excitation power within the studied range, while UC emission was found to saturate after a certain pump power. The increase in PA signal is due to the increase in non-radiative transitions in the sample. The wavelength-dependent photoacoustic spectrum of sample has shown absorption bands around 445, 536, 649 and 945 (970) nm with maximum absorption at 945 (970) nm. This indicates its potential for photo-thermal therapy using infrared excitation.