Study On The Upconversion Luminescence Properties Of Er³⁺, Tm³⁺, Yb³⁺ Doped Alkaline-earth Stannate Compound Nanocrystals

Rare-earth (RE)-doped upconversion luminescence materials for conversion of efficient infrared into visible or ultraviolet light are very attractive for modern technology. These materials have a variety of potential applications in several areas, such as color displays, sensors, detection of infrared radiation, and upconversion lasers. White UC luminescence has received great attention because of the sources for a variety of application purpose. So the generation of white UC luminescence would be particularly feasible and interesting. Perovskite alkaline-earth stannate ASnO3, where A = Ca, Sr and Ba, are extensively investigated due to their unusual dielectric and semiconducting properties, and extensive application in gas or humidity sensors, lithium ion batteries, thermally stable capacitors, and photocatalytic utilization. In this thesis, We report here on the preparation of pervoskite-type ASnO3:Er3+ (A = Ca, Sr, and Ba) and CaSnO3:Er3+-Bi3+ nanocrystals via hydrothermal synthesis and their upconversion luminescence properties.UC fluorescences in Er3+, Tm3+ and Yb3+ ions doped CaSnO3 crystals have been studied. The significant results are listed as follows:1. ASnO3:Er3+ (A = Ca, Sr, and Ba) were prepared by a hydrothermal method. It is seen that these three nanocrystals can give the green emission and red emission, which are attributed to the intra-4f transition of 4H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions, respectively. The order of the emission intensity (CaSnO3 > SrSnO3 > BaSnO3) is consistent with that of the tilting distortion of the SnO6 octahedral from CaSnO3 to SrSnO3 to BaSnO3, implying that the luminescence intensity of Er3+ is dependent on the structural distortion of stannates.2.The investigation of the upconversion luminescence of Er3+-Bi3+ codoped CaSnO3 nanocrystals indicates that Bi3+ ions could largely sensitize the emission of Er3+ ions which was attributed to the efficient energy transfer from Bi3+ to Er3+ ions and the modification of the local symmetry of Er3+ ions. The results show that the CaSnO3:Er3+-Bi3+ nanocrystals have potential application for fabricating visible upconversion devices. 3. Er3+, Tm3+ and Yb3+ ions codoped CaSnO3 nanocrystals are synthesized. Bright white upconversion luminescence in Er3+-Tm3+-Yb3+ doped CaSnO3 nanocrystals is obtained under diode laser excitation of 980 nm. The white light are composed of red, green and blue three primary colors which originate from the transitions of 4F9/2→4I15/2, (2H11/2, 4S3/2 )→4I15/2 of Er3+ ions and 1G4→3H6 of Tm3+ ions, respectively.4. It is observed that Tm3+ ions acts as the quenching center for green upconversion luminescence from Er3+ ions, but as sensitizer for red and blue luminescence when the doping concentration of Tm3+ ions less than 0.3 mol %. This is interpreted in terms of the efficient energy transfer between Tm3+ and Er3+ ions.