Up-conversion Phosphors via Rare Earth Doping
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Solution Overview
Problem
Current up-conversion materials exhibit low efficiency in converting near-IR radiation to visible light, with efficiencies ranging from 10^-13 to 10^-6 cm^2W^-1, limiting their application in lighting and laser technologies.
Innovation Solution
Development of ordered oxyfluoride compounds with specific rare earth ion doping and defect introduction, such as Sr-based oxyfluoride compounds with nitrogen incorporation, to enhance up-conversion efficiency by facilitating multi-photon absorption and energy transfer processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional up-conversion materials are used, then near-IR to visible light conversion is achieved, but the conversion efficiency is extremely low (10^-13 to 10^-6 cm^2W^-1)
Solution Approach 1:
The patent employs composite phosphor systems combining multiple rare earth activators (e.g., Yb3+ with Tb3+, or Yb3+ with Ce3+) in oxyfluoride host matrices. This composite approach enables synergistic energy transfer where Yb3+ absorbs near-IR photons and transfers energy to the secondary activator for visible emission, achieving significantly enhanced up-conversion efficiency compared to single-activator systems
Solution Approach 2:
The patent systematically varies compositional parameters including rare earth ion concentrations, oxyfluoride ratios, and dopant levels to optimize energy transfer efficiency. By controlling the concentration of activators and adjusting the O/F ratio in the host lattice, the patent achieves maximum up-conversion efficiency while minimizing energy losses
2Illumination intensity
If multi-photon absorption processes are used to achieve up-conversion, then visible light emission is obtained, but the process efficiency remains insufficient for practical applications
Solution Approach 1:
The patent uses Yb3+ ions as intermediary sensitizers that absorb near-IR photons and transfer energy to secondary activators (Tb3+, Ce3+, etc.). This intermediary mechanism converts the inherently inefficient direct multi-photon absorption into a more efficient sequential energy transfer process, reducing energy losses and enhancing visible light emission intensity
Solution Approach 2:
The patent replaces direct optical multi-photon absorption with a chemical/quantum mechanical energy transfer mechanism through dopant-dopant interactions. By substituting the direct photon-photon interaction with phonon-mediated energy transfer between rare earth ions, the system achieves higher efficiency in converting near-IR to visible light
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution significantly improves up-conversion efficiency, enabling the conversion of near-IR radiation to visible light with enhanced luminescence, suitable for next-generation lighting and laser applications.
Implementation Method 1
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.
Implementation Method 2
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.
Implementation Method 3
Another two photon process is second harmonic generation: exciting KH2PO4 or KNbO3 with 1064 nm laser light from a Nd3+ YAG an emission in the green at 532 nm is observed.
Data Source
AI summary
Light emitting devices that include an energy source configured to generate light energy and an up-conversion phosphor configured to emit light having a wavelength shorter than that of the light energy generated from the energy source are provided. The up-conversion phosphor comprises an ordered oxyfluoride compound having a formula: A3−3a/2RaMO4−δ1−w′F1−δ2−w″Nw. Methods are also generally disclosed for up-converting light energy.