| In recent years, there has been a continuous interest in the upconversion study of rare earth ion-doped materials due to the wide applications of short-wavelength solid-state lasers. Visible upconversion luminescence of different rare earth ion-doped materials has been investigated extensively under infrared excitation. But relatively few papers were devoted to the studies of ultraviolet and visible upconversion luminescence under visible excitation. In this paper, by the time-resolved laser-induced fluorescence technique, we focused on the studies of ultraviolet and visible upconversion in Er3+:YAG, Er3+:YAP, Tm3+:ZBLAN, Tm3+/Tb3+:ZBLAN, Pr3+:ZBLAN and Pr3+:Y2SiO5 materials. Moreover, the kinetics of fluorescence decay in these materials were also investigated because they are necessary to provide the knowledge for realizing laser emission and optimizing lasing efficiency.Firstly, we focused on the studies of upconversion and luminescence kinetics in Er3+:YAG and Er3+:YAP crystals.a) The violet and green fluorescence spectra and the kinetics of fluorescence decay in Er3+:YAG crystal under 408.6nm excitation were investigated. The influence of multiphonon and energy transfer on the fluorescence decay of the 4S3/2 multiplet was theoretically analyzed. A good agreement of the measured and the simulated decay curves was achieved. The continuous profile variety of the decay curves in the region from 548 nm to 561.2 nm was found and it originates from the fluorescence overlap of 2G9/2 and 4S3/2 and the intensity ratio dominates the profile.b) Ultraviolet (320 nm) and violet (405 nm) upconverted luminescence in Er3+:YAG and Er3+:YAP crystals has been investigated under blue laser excitation of the 4F7/2 multiplet. The upconversion mechanisms were studied in detail based on upconversion luminescence intensity dependence and decay profiles. Upconversion luminescence was attributed to energy transfer processes in high concentration Er3+:YAG and excited state absorption processes in low concentration Er3+:YAP, respectively.c) Ultraviolet (320 nm), violet (405 nm and 417 nm) and blue (474 nm) upconversion luminescence in Er3+:YAG were observed under 524.4 nm excitation of the 2H11/2 multiplet. Excitation spectra show that upconversion luminescence is more intense under 524.4 nm excitation of 2H11/2 than 4S3/2. The upconversion mechanisms were discussed in detail based on upconverted intensity dependence and decay curves. Excitation state absorption and energy transfer upconversion were proposed to explain observed upconversion phenomena. d) Ultraviolet and visible upconversion luminescence from the 4S3/2, 2G9/2 and 2P3/2 levels have been observed in Er3+:YAG following 647.2 nm excitation of the 4F9/2 multiple. The measured decay profiles were theoretically fitted by kinetics theory and the basically good agreements were achieved. The results indicate that some energy transfer processes proposed to explain the observed upconversion phenomena are reasonable.Secondly, we focused on the studies of upconversion and luminescence decay kinetics in Tm3+ and Tm3+/Tb3+ doped ZBLAN glasses.a) The relaxation of the 1I6, 1D2, 1G4 and 3H4 levels of Tm3+ ions has been investigated by the analysis of the fluorescence decay curves in Tm3+ and Tm3+/Tb3+ doped ZBLAN glasses. The lifetimes of these levels were obtained by e-exponential fitting their decay curves. The effects of Tm3+ concentration and Tm3+-Tb3+ interaction on the relaxation of the 1I6, 1D2, 1G4 and 3H4 levels of Tm3+ were investigated by the analysis of the fluorescence decay curves and lifetimes, which were interpreted by several energy transfer processes.b) Ultraviolet upconversion emission properties have been studied under 463nm laser excitation in Tm3+:ZBLAN glass. Two ultraviolet emission bands, centered at 347nm and 362nm have been observed. The responsible upconversion mechanisms were investigated and attributed to excited-state absorption.c) Ultraviolet and blue upconversion luminescence bands around 362 and 450 nm were observed by 655 nm laser excitation in Tm3+ and Tm3+/Tb3+ doped ZBLAN glasses. The upconversion mechanism was attributed to excited-state absorption by analyzing the decay profiles and the intensity dependence.Finally, we focused on the studies of upconversion and luminescence decay kinetics in Pr3+:ZBLAN glasses and Pr3+:Y2SiO5 crystal.a) The lifetimes of 3P0 and 1D2 levels of Pr3+ were measured in ZBLAN glasses by resonant excitation. Energy transfer observed between Pr3+ ions was analyzed by energy transfer theory. The non-exponential dependence of the 1D2 decay on Pr3+ concentration indicates that dipole-dipole interaction between Pr3+ ions is the main energy transfer process. Orange-to-blue upconversion luminescence was observed and described by two-ion energy transfer mechanism. The temporal evolution of upconversion luminescence was characterized by rise and decay times related to the dopant concentration.b) The luminescence properties of the 1S0 level in Pr3+:ZBLAN glass was investigated by the two-step excitation process 3H4→1D2→4f5d. The 1S0 emission and the photon cascade emission were observed. The position of 1S0 energy level was determined to be 46576.6 cm-1. The values of some optical parameters, such as branching ratios, lifetimes, and emission cross sections, were determined. The effect of the configuration mixture between the 1S0 level and 4f5d configuration on 1S0 luminescence properties was discussed. Moreover, by the other two-step excitation process 3H4→3P0→4f5d, the 1S0 emission was also observed.c) Ultraviolet broad emission from 265 nm to 360 nm was observed in Pr3+:Y2SiO5 crystal pumped by 532 nm Nd:YAG laser. The two-photon simultaneous absorption process is found to be responsible for the ultraviolet broadband emission based on the fluorescence intensity dependence on the pump power as well as the related spectroscopic analyses. This study provides a new route to produce UV broadband luminescence by convenient 532 nm Nd:YAG laser, which is potentially useful for realizing UV solid-state tunable lasers.
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