Over the decades, Er3+ ions doped materials have been of great interest as they can be used to convert near InfraRed (NIR) wavelength to shorter wavelengths as a result of the absorption of two or more photons. This process is known as upconversion. Phosphate glasses can incorporate large amount of Er3+ ions. They have also numerous advantages over other glasses such as silicate and germanate glasses for example, as they can be processed using low processing temperature. However, phosphate glasses have a high phonon energy, which is disadvantageous to the upconversion process. A large amount of Er3+ ions is then needed to achieve upconversion in such glasses. As the spectroscopic properties of the Er3+ ions depend on their local environment, the intensity of the upconversion from an Er3+ doped phosphate glass can be increased by enhancing the local crystals field. This could be achieved by developing a phosphate glass which contains Er3+ doped fluoride crystals.
Crystals in glass could be obtained by heat-treating a glass. However, as it is not possible to predict and control the precipitation of Er3+ doped fluoride crystals with a specific crystalline phase in the volume of the glass using such heat treatment, the direct doping method has been developed and optimized to add NaYF4: Er3+, Yb3+ crystals in phosphate glasses.
“Although crystallization and direct doping methods have been used to prepare various glasses, a deeper knowledge and understanding of their nucleation and growth mechanism and of the direct doping process still remain necessary for the development of novel phosphate glasses with enhanced spectroscopic performances” says Nirajan.
This thesis led to a better understanding of the composition-structure-property relationships, nucleation and growth process and the direct doping method and so to the development of promising new glass-ceramics and crystals containing glasses with strong upconversion under NIR pumping. Results from this work were published in 5 publications included in the thesis.
MSc (Tech) Nirajan Ojha comes from beautiful country of Mt. Everest and birthplace of Buddha, Nepal. He currently works as a doctoral researcher in Photonic Glasses group, led by Associate Professor Laeticia Petit, in Photonics Laboratory at Tampere University.
The doctoral dissertation of MSc (Tech) Nirajan Ojha in the field of Photonic Glasses titled Investigation of upconversion properties from active crystals in oxyfluorophosphate glasses will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University on Friday 6th November 2020 starting at 12 O’ clock. The Opponents will be Professor Dominik Dorosz from AGH University of Science and Technology in Krakow Poland and Professor Enrico Bernardo from University of Padova Italy. The Custos will be Associate Professor Laeticia Petit from the Faculty of Engineering and Natural Sciences, Tampere University, Finland.
Due to the coronavirus situation, the event can be followed via remote connection.
The dissertation is available online at http://urn.fi/URN:ISBN:978-952-03-1716-4
Photo: Laeticia Petit