Coating Luminescent Phosphors for Lighting and Display Applications
Tech ID: 21271 / UC Case 2010-757-0
Method of coating luminescent phosphors, for lighting and display applications, with nanoscale ZNO films using atomic layer deposition (ALD) - for improved efficacy, thermal stability, and lifetime.
The invention is a new way of coating luminescent phosphors used for lighting and display applications. It is common practice to coat phosphors particles to improve the electrical and/or thermal conductivity, to passivate the particle surface in a manner which reduces the amount of non-luminescent "dead-space" material, and to improve the surface conditions in a manner which enables adhesion to a substrate (glass envelope of a lamp or the faceplate of a display). Current practice is to coat the particles and then deposit the particles onto the substrate. This typically requires a "binder", such as non-luminescent silicates, to make adherence to the substrate possible.
Present invention entails the deposition of the uncoated phosphor particles onto the substrate, followed by subsequent coating, in-situ, with nano-scale ZnO using Atomic Layer Deposition (ALD). This allows adhesion of the luminescent phosphors onto the substrate without the use of non-luminescent binders. The elimination of silicate (or other) binders allows for an increase in luminous efficacy (efficiency) of the phosphor, as well as elimination of a thermal insulator from the process.
The nanoscale coating of ZnO binds the phosphor onto the substrate. ZnO is a good thermal conductor. Also, the very thin layer of ZnO does not degrade the luminous efficacy of the luminescent phosphor particles being coated.
The electrical conductivity of the ZnO is sufficient to provide a conductive path of electrons away from the phosphor, during operation, and thereby prevent charging of the particle. The subsequent result is an improvement of efficacy of the phosphor particle, as well as the entire luminescent phosphor layer on the substrate.
The good thermal conductivity of the ZnO coating helps dissipate heat from the phosphor layer. The consequence of this process is improved efficacy and lifetime of the phosphor layer through the resultant lower-temperature operation.
The luminous properties of the nano-scale ZnO coating passivates the surface states of the phosphor, potentially improving the efficacy of the phosphor.
Interception by the ZnO coating of energy (photons or electrons used to excite the phosphor particles), results in a luminescent process within the ZnO itself, since it is both a photoluminescent as well as cathodoluminescent material.
- Less complicated than current standard phosphor deposition methods;
- Better heat dissipation, no phosphor overheating;
- Less efficacy degradation during phosphor lifetime;
- No usage of limited resource materials such as Indium Oxide.
- Chubun NN, Chakhovskoi AG, and Hunt CE. 2003. Efficiency of cathodoluminescent phosphors for a field-emission light source application. Journal of Vacuum Science & Technology B : Microelectronics and Nanometer Structures. 21(4):1618-21.
- Park JH, Park BW, Choi NS, Jeong YT, Kim JS and Yang JS. 2008. Enhancement in Cathodoluminescent Properties of Carbon Nanotube-ZnGa2O4:Mn2+ Phosphor Composites. Electrochem. Solid-State Lett., 11(2):J12-J14.
- Tapily K, Stegall D, Gu D, Baumgart H, Namkoong G and Elmustafa A. 2009. Physical Characterization of Zinc Oxide Thin Films Grown by ALD. ECS Transactions. 25(4):85-92.
- Hunt, Charles E.