Research On The Photon Avalanche And Emission Bistability In Tm Ion Doped ZrO₂Nanocrystals

Rare-earth-ion Tm doped nanophase materials have important potential applications insolid-state blue laser, high-density optical storage and multifunctional optical display due tothe high efficiency of visible blue upconversion emission. In the thesis, we experimentallyinvestigated the dynamics of photon avalanche （PA） luminescence in Tm ion-doped ZrO₂nanocrystals, and the characteristics of intrinsic optical bistability of the upconversionemission in Yb ion-sensitized Tm:ZrO₂nanocrystals. The particular physical mechanisms ofthe PA luminescence and the intrinsically bistable emission were analyzed theoretically.Tm:ZrO₂nanocrystal materials with various dopant concentrations were prepared by acombustion method. The component, morphology, particle size and crystallite phase werecharacterized. Employing a653nm avalanche wavelength laser as excitation source, weachieved the efficient luminescence of upconverted475nm blue and downconverted830nmnear-infrared （NIR） spectra. At room temperature, we studied both the steady-state PAperformance and the transient excitation kinetics of Tm:ZrO₂nancrystals. The distinctthreshold behavior of PA and the critical slowing phenomenon were observed experimentally.The dependences of photoluminescence threshold, PA threshold and the efficiency of PAluminescence on Tm ion-doped concentration were discussed, and then the optimum dopantconcentration was given. We experimentally performed the efficient PA luminescence with athreshold below milliwatt order, correspondingly, the excellent performance of PA showed inTm:ZrO₂nanocrystals were presented.Based on rate equation theory, we established the PA physical model of Tm ion dopedsystem under653nm laser excitation. We numerically simulated the steady-state pumpingdynamics of the level populations on the Tm ion ground-and excited-states, and the nonlinearreverse saturable absorption behavior. The effects of the dominant physical parameters on PAthreshold and luminescence intensity were disccused. Moreover, we numerically simulatedthe transient time-evolution kinetics of Tm ion level populations under653nm rectangularpulse excitation, and demonstrated the critical slowing phenomenon. By comparing with theexperimental results, our theoretical modeling well predicted the steady-state PAcharacteristics and the transient kinetics responses in Tm:ZrO₂nanocrystals, consequently, themicroscopic physical processes of PA were reasonably understood. Tm:ZrO₂nanocrystals with low concentration2mol%and high concentration10mol%Yb ion dopant were prepared by a combustion method. The crystallite phase and nanoparticlemorphology were characterized through X-ray diffraction, scanning electron microscope andtransmission electron microscope. At room temperature, we employed a973nm diode laser asexcitation source, and experimentally measured the upconversion fluorescence spectra invisible and NIR spectra domain. The particular mechanisms of sensitized energy transferupconversion for the different Yb ion doped concentration were analyzed. Furthermore, weexperimentally studied the characteristics of intrinsically bistable upconversion emission at480nm blue,680nm red and800nm NIR spectra bands, respectively. The physicalmechanisms of intrinsic bistability emission in Tm:ZrO₂nanocrystals were discussedrespectively for the cases of the low and high Yb dopant concentrations.