Description:
Reference #: 00838
The University of South Carolina is offering licensing opportunities for this technology
Potential Applications:
Frequency up-conversion luminescence has great potential applications in diode-pumped all-solid-state visible lasers, highly efficient next-generation lighting, near-IR photon detectors, high power fiber up-conversion lasers, nm-sized biological labels and new emissive displays. Up-to-date rare earths have mainly been doped into oxyfluoride glasses since oxyfluorides combine the favorable low phonon energy and high up-conversion efficiencies with the high mechanical and chemical stabilities of oxides.
Advantages and Benefits:
• Highly efficient process
• High-powered system
• More efficient system than cooperative sensitization
Invention Description:
Up-conversion or anti-Stokes processes occur in materials capable of absorbing photons at energies lower than the subsequently emitted photons. These materials can convert near-IR radiation to light in the visible part of the electromagnetic spectrum. In up-conversion processes, either single-photon or multi-photon excitations take place. One well-known up-conversion process is the excitation of anti-Stokes emission bands in Raman spectroscopy, where a lower energy photon is converted to a higher energy one and the additional energy required is provided by lattice when one or more phonons are annihilated. This is a very inefficient process: in Si the anti-Stokes Raman emission has an efficiency of 10-13 cm2W-1.
In a two-photon up-conversion process a virtual intermediate state exists, while both ground and excited states are real. The two-photon up-conversion process requires that the sum of energies of the two exciting photons be larger than the band gap energy and the simultaneous absorption of two photons is an inherently less efficient process than single photon absorption. Another process relies on the sequential absorption of two photons by two different activator ions and their subsequent decay into their ground states from a virtual excited state while emitting photons with energies equal to the sum of the energies of the individual ions. The final state is a real and therefore this cooperative sensitization is more efficient than cooperative luminescence. In Yb3+, Tb3+: YF3 the sensitization of Tb3+ from Yb3+ activators has an efficiency of 10-6 cm2W-1.
Three photon up conversion processes are also known: in SrF2: Er3+ up to three 1 um photons can be absorbed sequentially by Er3+ allowing emission in the blue, green or red regions of the electromagnetic spectrum. In the process a real intermediate state is needed since only at a finite life time of this state can the initial excitation be further promoted by a second excited photon. Other systems where three-photon absorption and up-conversion processes have been established are Er3+:YF3 and Tm3+, Yb3+:NaYF4. In the latter system 4-photon processes are also possible.