Разгорание и затухание импульсной катодолюминесценции в монокристаллах и керамиках Nd:ИАГ

The kinetics of pulsed cathodoluminescence of Nd3+ ions in Nd:YAG single crystals and ceramic samples was studied. In these substances, luminescence appears after the ending of exposure by an electron beam with a duration of 2 ns. Optical transitions are observed from the 2F2 5/2 level and manifest themselves in the ultraviolet and visible regions of the spectrum, and from the 4F 3/2 level – in the near infrared region. The kinetics of luminescence is characterized by a rise and a decay and is described by the difference between two exponential functions. It has been determined that the characteristic decay times of luminescence are the lifetimes of the 2F2 5/2 and 4F 3/2 radiative levels, and the time of a rise is determined by the pumping mechanism. Moreover, the pumping of the uppermost Stark component of the 2F2 5/2 level occurs in the process of linear recombination of the ionized neodymium ion with free electrons, and the 4F 3/2 level is due to nonradiative transitions from the upper levels.

NONINVASIVE ESTIMATION OF THE LOCAL TEMPERATURE OF BIOTISSUES HEATING UNDER THE ACTION OF LASER IRRADIATION FROM THE LUMINESCENCE SPECTRA OF Nd3+ IONS

Laser hyperthermia is one of the promising methods for treatment of oncological diseases. For routine clinical use of hyperthermia, it is necessary to control the uniformity and localization of heat within the tumor. Local heating can be achieved by using special thermal agents, such as nanoparticles doped with rare-earth ions. Measurement of the temperature of the thermal agents will allow timely regulation of the applied laser radiation excitation power and optimization of the hyperthermia process.The paper presents the results of a study on the non-invasive determination of the YPO4 nanoparticles doped with Nd3+ temperature with sensitivity of 0.2% °С-1 in 30-60°С temperature range. The temperature of the nanoparticles was calculated from the Nd3+ luminescence spectra in the 800-1000 nm range under excitation into 4F5/2 energy state by 805 nm laser. A calibration procedure for recalculating the ratio of the luminescence intensities from the Stark sublevels of the 4F3/2 Nd3+ state into the values of the real NP temperature in accordance with the Boltzmann distribution is given. An algorithm for calculating luminescence intensities for individual Stark components is proposed. After calculating the intensities corresponding to each individual Stark component, all the intensities related to the transition from the upper and lower Stark sublevels of the 4F3/2 state are summed, and then their ratio is calculated. The resulting ratio is normalized to the value of the ratio at room temperature and, in accordance with the calibration dependence, is recalculated into the NP heating temperature. It was demonstrated that the investigated 1%Nd3+:YPO4 nanoparticles can be used as "primary” thermometers that do not require additional recalibration to evaluate the temperature in the range used for hyperthermia.