20 new things for today

1. I had lunch with Tony (he serves as the instructor for the junior students).
   
   1. During the lunch I realized that I should have paid more attention to the brand names of the tools, for he asked several times about the names which I cannot tell.
      
   2. He also mentioned that it is important to initiate, when I said there are relatively less casual talks on science compared with that abroad. He also encouraged me to initiate a party inviting all the Northeastern people of China in this institute, if I want to get to know people from other areas.
      
   3. He said he works 13 hrs a day.
      
   4. He pushed himself to read by listing the books, when he was in college. He doesn't need the list now, for he already got used to reading every day.
      
2. We use different lenses, and we differentiate them by their focal length (by saying focal length we simplify the lens set as one piece of lens). Larger focal length--like in our lab we have 105mm, 85mm, and 50mm lenses—means lower optical power, which is associated with larger magnification of distant objects, and a narrower angle of view. Conversely, shorter focal length or higher optical power is associated with a wider angle of view. In our lab we make two lenses connected front to front, and this makes the rears of the lenses facing cortex and CCD, separately. Fine adjustments should be made to make sure the cortex captured sharply on the CCD, which includes adapter applied between lenses or between lens and CCD, finely tuned distance between lenses and cortex, and etc.

20 new things for today

1. Agar cools quicker than I anticipated. Drop 3-4 drips of it and screw the ring quickly.
   
2. Japan releases Chinese trawler captain, but refuses to apologize. It is said that China's banning on raw material (Rare earth) exportation to Japan, which is crucial for the high-tech industry in Japan, is the real stirring response for the Japan's release.
   
3. One of the usages of rare earth elements is to produce phosphor. Got its name from element of phosphorus, but phosphor has a completely different mechanism on lightening—the former is because of chemiluminescence (some oxidization-reduction reaction), whereas the latter is because of phosphorescence (slow decay, >1ms) or fluorescence (quick decay, tens of nanoseconds).
   
4. But why materials made of rare earth element emit light? Simply put, it's because of the electronic band structure in the crystals. An incoming particle (such as a UV photon) excites an electron from the valence band (trapped and cannot move under usual state) to either exciton band or conduction band. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). As for the elections excited to the conduction band, the holes associated with them in the conduction band are independent (compared to the loosely bound pairs in exciton band). Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states, slowed down by reliance on the low-probability forbidden mechanism, again results in light emission (slow component).
   
5. Usage? Lighting, mainly on fluorescent lamps, and on some occasions used on metal halide lamps. Glow-in-the-dark toys. Electroluminescence (used commonly in LCD backlights). White LED (turning the blue light from LED into white). Cathode ray tube (television).