Optical Properties of Lanthanide-Doped Oxysulfides and Oxyfluorides


Student thesis: Doctoral Thesis

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Awarding Institution
Award date2 Apr 2019


Luminescence originating from f-f and f-d transitions of lanthanide ions has been extensively studied in the past few decades. Great efforts have been focused on the development of lanthanide-doped sulfides, fluorides and oxides as luminescent materials for various applications. Oxysulfides and oxyfluorides which possess interesting properties that are different from pure sulfides, fluorides and oxides have attracted more attention in recently years. In order to further exploit the potential of lanthanide-doped luminescent materials, we concentrate on investigating the optical properties of lanthanide-doped oxysulfides and oxyfluorides in this thesis. By developing new synthesis protocol, we are able to achieve high brightness mechanoluminesce (ML) of lanthanide ion in CaZnOS and upconversion (UC) emission of Pr3+ from visible to ultraviolet (UV) in Lu6O5F8 nanocrystals that to the best of our knowledge have never been reported before.

This thesis begins with a review of the recent progress in the development of ML materials with particular emphasis on lanthanide ML in oxysulfides and upconversion luminescence of Pr3+ in oxyfluorides. The novel properties of oxysulfides and oxyfluorides would open up new opportunities for new technological applications.

In chapter 4, we reported a general strategy for expanding the emission spectra of ML through doping of various lanthanide activator ions. We developed a lithium-assisted annealing method for effective incorporation of luminescent lanthanide (e.g.; Tb3+, Tm3+, Eu3+, Pr3+, Sm3+, Er3+, Dy3+, Ho3+, Nd3+, and Yb3+) ions into CaZnOS crystals that are identified as one of the most efficient host materials for ML. These doped CaZnOS crystals show efficient and tunable ML spanning the ultraviolet to near infrared spectral regions. The multicolor ML materials were used to create encrypted anti-counterfeiting patterns, which produce spatially resolvable optical codes under single-point dynamic pressure of a ball-point pen.

In chapter 5, we developed a one-step thermal decomposition method for synthesizing Pr3+-doped lutetium oxyfluorides. We studied the downshifting and UC properties of Pr3+ and revealed the two photon UC mechanism in Pr3+. Lutetium oxyfluorides make a trade-off between suitable location of Pr3+ 5d band for energy match of two blue photons and medium phonon energy to enable enough lifetime of intermediate 3P0 energy level. Both requirements are very crucial for the generation of UC luminescence. Notably, efficient energy transfer from Pr3+ to Gd3+ was discovered in the host material and UC emission of Gd3+ was achieved. Moreover, we presented the microbial inactivation application by taking advantage of upconverted UV light under 450nm blue laser excitation.

In chapter 6, we used a hot-injection method to synthesis Pr3+ and Gd3+ co-doped monodisperse lutetium oxyfluoride nanocrystals. Upconversion emission of Gd3+ at 315nm under blue laser excitation was successfully observed in colloidal solutions. We employed the nanocrystals as a gain medium to realize deep UV lasing action through the formation of whispering gallery mode in a microcavity under 450 nm pulse laser excitation. Our results highlight the promising future of realizing deep ultraviolet regime lasing through visible laser excitation for different applications.

    Research areas

  • Lanthanide, Mechanoluminescence, Upconversion, Oxysulfides, Oxyfluorides, Nanocrystals, Color coding, Microbial Inactivation, Deep ultraviolet lasing