Viabilidade de sistemas dopados e co-dopados com Yb3+ e Nd3+ para aplicações fotônicas - lasers e termometria óptica

Abstract

In this work, we investigated the spectroscopic characteristics of Nd3+ and Yb3+ doped/co-doped materials for potential applications in photonic devices, particularly lasers emitting in the IR and visible (blue) and thermal sensing operating in the first and second biological windows. For such purposes, we used the fluorescence spectroscopy technique in steady state and time resolved. Initially we investigated the spectroscopic characteristics of the Yb3+ doped oxyfluoride glass, analyzing three important effects present in Yb3+ doped systems: Radiation Trapping (RT), Self-Quenching (SQ), and Cooperative Luminescence (CL). We show that the effects of RT and SQ affect substantially the line shape of Yb3+ emission spectrum, thereby inducing miscalculations of the emission cross section, overestimation of the laser level lifetime, as well as errors in non-radiative decay rates. On the other hand, we show that the strong presence of RT favors the CL effect between Yb3+ ions, which configures an advantageous feature for the generation of blue light via CL. In the thermal sensing context, we carried out a study on application of Nd3+ single doped materials for optical temperature sensors based on Fluorescence Intensity Ratio (FIR) using the 4F3/2, 4F5/2 and 4F7/2 Nd3+ energy levels, more precisely, Nd3+ doped Q-98 phosphate glass, where we showed that the investigated phosphate glass present good perspectives for applications in optical thermometer, being its thermal sensitivity and the maximum thermal range, strongly dependent on the considered energy levels. Following the studies on thermal sensing, we investigated the effects of structure core and core@shell of lanthanum fluoride nanocrystals (LaF3) doped/co-doped with Nd3+ and Yb3+ for temperature sensor based on energy transfer (ET). For this, LaF3 nanocrystals in structural configurations LaF3:Nd (only core), LaF3:Nd/Yb (only core), LaF3 :Nd@LaF3:Yb (Nd3+ in core and Yb3+ in shell), and LaF3:Yb@LaF3:Nd (Yb3+ in core and Nd3+ in shell) were synthesized. We evaluated the FIR of the emission from Yb3+ (2F5/2→2F7/2 at ~990 nm) and Nd3+ (4F3/2→4I13/2 at ~1060 nm) against the temperature and we concluded that their sensitivities are strongly dependent on the structural configurations, i.e., we get control the ET processes and their temperature dependence. In addition, we show that FIR, using 990 and 1330 nm emissions present thermal sensitivity at least one order of magnitude greater that the other FIR’s.