Hafnium Oxide Film + UV Excitation = White Light
Researchers have shown growing interest in the development of novel phosphors that can be excited via ultraviolet (UV) light emitting diodes (LEDs). One of the solutions involves hafnium oxide (HfO2) films, which produces a white light emission when excited at 270 nm. The reason is the need to enhance the efficiency of white light emitting devices for use in next-generation lighting lamps.
For those of you who are less familiar with hafnium (atomic number 72), it is a lustrous, silvery gray, tetravalent transition metal. It chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted in 1869 and was named for Hafnia, the Latin name for Copenhagen where it was discovered.
Cameron Chai, in a recent article posted on azom.com , reported that for the first time, cold white light has been generated via simultaneous emission of red, green and blue emitting centers upon UV excitation. This has been accomplished by using borate-based glasses that include Mn2+, Tb3+ and Ce3+ ions as activators (… ain’t that a lot of elements named in one sentence). Ce3+ ions have wide absorption bands in the UV and hence they can be activated using LEDs. The benefits offered by commercial LEDs are reduced size, durability and low energy consumption.
Chai goes on to report that HfO2 films is doubly doped with TbCl3 and CeCl3 and triply doped with MnCl2, TbCl3 and CeCl3. The yellow and red emissions of Mn2+ ions and the yellow and green emissions of Tb3+ ions can be produced by UV excitation through an energy transfer from Ce3+ to Mn2+ and Ce3+ to Tb3+. The efficiency of energy transfer in the HfO2 films is improved by increasing the concentration of Mn2+ ion to approximately 76%. In addition, the films can produce white light emission when they are excited at 270 nm, a peak wave length of AlGaN/GaN-based LEDs.
If you’d like to peruse Chai’s original article, just click on http://www.azom.com/news.aspx?newsID=32516
As an aside, AZoM.com, which stands for the ‘A to Z of Materials’ is a very interesting site for those interested in the use of Advanced Materials by the engineering and design community worldwide. AZoM is focused on the needs of the end users of materials. To achieve this aim, all of the educational, informative and news content on AZoM is easy to access and search and is provided on a free of charge, no subscription, no charge per article, totally free basis… the price is right!!
AZoM is apparently assisted by team of world-renowned materials experts by providing strategic direction, help and guidance. These experts are primarily UK and Australia based, although I noted that Prof. Mary Anne White of Dalhousie University in Canada is on the roster. http://www.azom.com/aboutus.aspx Guess I’ve got to give her a call.
Until soon… Ian