Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

During the past few decades, the research on persistent luminescent materials has focused mainly on Eu2+-doped compounds. However, the yearly number of publications on non-Eu2+-based materials has also increased steadily. By now, the number of known persistent phosphors has increased to over 200, of which over 80% are not based on Eu2+, but rather, on intrinsic host defects, transition metals (manganese, chromium, copper, etc.) or trivalent rare earths (cerium, terbium, dysprosium, etc.). In this review, we present an overview of these non-Eu2+-based persistent luminescent materials and their afterglow properties. We also take a closer look at some remaining challenges, such as the excitability with visible light and the possibility of energy transfer between multiple luminescent centers. Finally, we summarize the necessary elements for a complete description of a persistent luminescent material, in order to allow a more objective comparison of these phosphors.

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Persistent Luminescence in Non-Eu2+-Doped Compounds: A Review.

Persistent luminescence instead of phosphorescence: History, mechanism, and perspective

In this letter, the resistive switching properties of a ZrO2-based memory film with implanted Ti ions are investigated. The testing results demonstrate that doping Ti in ZrO2 can remove the electroforming process and reduce the variations of switching parameters such as set voltage and resistance in off state. Furthermore, the Ti-doped ZrO2 resistive switching memory also exhibits high device yield (nearly 100%), low operating voltage, fast speed, large on/off ratio (>104), and long retention time (>107 s). The formation and rupture of conducting filaments are suggested to be responsible for the resistive switching phenomenon. The doped Ti impurities can improve the formation of conducting filaments and switching behaviors.

Improvement of Resistive Switching Properties in $ \hbox{ZrO}_{2}$ -Based ReRAM With Implanted Ti Ions

A novel blue-emitting long-lasting proyphosphate phosphor Sr2P2O7:Eu2+.Y3+

Nanocrystalline ZrO2 fine powders were prepared via the one-pot reaction followed by annealing from 700 to 1100 °C in air. It is believed that generation of excess oxygen vacancies within nanocrystalline ZrO2 is primarily responsible for room-temperature tetragonal phase stabilization below a critical size, and the phase transformation from tetragonal to monoclinic ZrO2 happened in the annealing process. Luminescent properties of ZrO2 were greatly affected by oxygen vacancies in the phase transition process. Two bands centered at 350 and 470 nm were observed in tetragonal ZrO2. The electrons trapped by oxygen vacancies creating F centers recombined with holes yielding the 350 nm luminescence. Temporal decay of the 470 nm luminescence is due to the detrapping of electrons to the Ti3+ luminescence centers. Elevated temperature accelerated the phase transformation to monoclinic ZrO2 and decreased the oxygen vacancy concentration, resulting in a decrease of the 350 nm emission and enhancement of the 470 nm ph...

http://bec01.phy.georgiasouthern.edu/xwang/research/JPCC%20Cong%20Yan2%2009.pdf

Effect of Oxygen Vacancy on Phase Transition and Photoluminescence Properties of Nanocrystalline Zirconia Synthesized by the One-Pot Reaction

Long lasting phosphorescent properties of Ti doped ZrO2

Uniform and cube-structured RE 3+ (RE = Pr,Tb)-doped CaSnO 3 phosphors have been successfully synthesized by a two-step approach including the room-temperature synthesis of CaSn(OH) 6 precursors with the help of cetyltrimethylammoniumbromide surfactant and then converted to CaSnO 3 by calcination at 750°C. The decomposition process of the Casn(OH) 6 precursor, crystallization, and morphology of the as-synthesized CaSnO 3 phosphors have been investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. Furthermore, luminescence properties of CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors, including photoluminescence, fluorescence lifetime, afterglow decay, and thermoluminescence, are also systematically discussed in this paper. The as-synthesized Pr 3+ and Tb 3+ doped CaSnO 3 phosphors show intense luminescence under ultraviolet excitation. Moreover, the afterglow emission from CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors lasts for more than 3 h after the ultraviolet irradiation source has been removed. Both the fluorescence and afterglow decay curves of the CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors contain one fast decay component and another slow decay process. Thermoluminescence spectra indicate that the incorporation of RE 3+ ions into the CaSnO 3 host produces suitable trapping centers, which are the origin of the long-lasting phosphorescence phenomenon in this kind of material at room temperature.

Synthesis and Luminescence Properties of Cube-Structured CaSnO3 ∕ RE3 + ( RE = Pr , Tb ) Long-Lasting Phosphors

Enhancement of the 4 T 1g ( 4 G) → 6 A 1g ( 6 S) red emission of MgGeO 3 :1% Mn 2+ with addition of Yb 2 O 3 is reported. The initial phosphorescence in the Yb 2 O 3 codoped sample is an order of magnitude stronger than that of the Yb 2 O 3 -free sample. Thermoluminescence spectra indicate that the introduction of Yb 3+ into the host produces traps with a suitable depth, resulting in the enhanced red phosphorescence of Mn 2+ . The possible mechanism for this phenomenon is explained by a competitive trapping model.

http://bec01.phy.georgiasouthern.edu/xwang/research/JES%20156%202009%20Cong%20Y.pdf

Enhanced Red Phosphorescence in MgGeO3:Mn2+ by Addition of Yb3+ Ions

A facile synthetic route to synthesize the nanocrystalline zirconia particles via preparing polyzirconoxane with zirconium tetraalkoxide is reported, and the luminescent properties of the so-obtained ZrO 2 :Ti nanophosphors are systematically investigated in this paper. The bluish-white photoluminescence and phosphorescence originating from the recombination of electrons trapped by anion vacancies and the holes created in the valence band, and the Ti 3+ ion substituting for Zr 4+ is assumed to be the luminescent center. The long afterglow from ZrO 2 :Ti is attributed to the oxygen vacancies caused by the addition of Ti 3+ ions into ZrO 2 host. Compared with the bulk ZrO 2 :Ti, the nanosized phosphors exhibit a longer persistent time because of the increased surface traps due to the large surface-to-volume ratio in the nanoparticles. This long persistent process can be elucidated by a simple possible mechanism.

Yan Cong

Papers

Effect of Oxygen Vacancy on Phase Transition and Photoluminescence Properties of Nanocrystalline Zirconia Synthesized by the One-Pot Reaction

Long lasting phosphorescent properties of Ti doped ZrO2

Synthesis and Luminescence Properties of Cube-Structured CaSnO3 ∕ RE3 + ( RE = Pr , Tb ) Long-Lasting Phosphors

Enhanced Red Phosphorescence in MgGeO3:Mn2+ by Addition of Yb3+ Ions

Synthesis and Optical Property Studies of Nanocrystalline ZrO2 : Ti Long-Lasting Phosphors