Investigation on the thermal effects of NaYF4:Er under 1550 nm irradiation.

The thermal effects of NaYF4:Er microcrystals under 1550 nm laser diode irradiation were investigated using an infrared thermal imaging method. The results revealed that the temperature of the LD irradiation beam area was non-uniform. The NaYF4:Er sample exhibits a rapid temperature increase within 5-10 s, and the heating process reaches its steady state after 60 s of irradiation when exposed to 1550 nm LD. The response time, temperature increase, and emission intensity of the samples depend on the excitation power density and concentration of doped Er3+ ions. Low excitation power density is required to avoid the influence of thermal effects on the up-conversion emission spectra measurement. Rapid scanning in up-conversion emission spectra measurement is not effective in preventing the heating effect under high excitation power pumping. In addition, a relative deviation of temperature, existing in fluorescence intensity ratio technique, decreased with the increasing irradiation time.