During photonic upconversion processes, phosphors absorb two or more photons in the excited state and emit light with energy greater than incident light in comparison to typical Stokes-shifted fluorescence. Recently, it is proposed that upconversion system would be adpated as a new type of security and encryption process when the upconversion materials are patterned thin or thick films. The signs of secured information are expressed not only in the form of patterns but also in various colors. Therefore, it is important to produce various colors of emission in order to enrich amount of information of upconversion films. In this study, upconversion films were fabricated on a quartz substrate using the pulsed laser deposition (PLD) method, and then the temperature and chemical environment were adjusted to wear various emission colors. In vacuum or inert gas (N<sub>2</sub>) environment, the overall emission intensity of trivalent erbium ions was enhanced with heat treatment emanating green color. On the other hand, in atmospheric environment, the emission color was transformed into red with the overall intensity decreasing. We studied the origin of the color and intensity change of upconversion emission of rare earth metals embedded in solid lattice which releases excitation energy mainly through non-radiative phonon relaxation. As a result, we elucidated the role of molecules in photophysical process with Infrared spectroscopy, x-ray photoelectron spectroscopy (XPS) and time resolved luminescence analysis.

Emission color tunability of upconversion film by modulating phonon relaxation

2019 Spring National Meeting

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