Down conversion

The nonlinear optical teclmiques of up- and down-conversion are based on mixing optical beams in a suitable crystal (BBO, LiNbO, KDP, etc) witli tire generation of new optical frequencies tire physical principle is as follows. If two beams having optical frequencies cOp CO2 and wavevectors k, are mixed in a nonlinear optical crystal at tire appropriate angle, a new optical frequency co can be coherently generated witli tire following conditions satisfied ... 

The sum-frequency case of co = co -t CO2 is called up-conversion, tire difference-frequency co = co - CO2 down-conversion, reflecting tire increase or decrease of tire generated optical frequency co from tire input frequencies co and 052-... 

Figure C3.5.2. VER transitions involved in the decay of vibration Q by cubic and quartic anhannonic coupling (from [M])- Transitions involving discrete vibrations are represented by arrows. Transitions involving phonons (continuous energy states) are represented by wiggly arrows. In (a), the transition denoted (i) is the ladder down-conversion process, where D is annihilated and a lower-energy vibration cu and a phonon co are created.

Overall, the partial pressure of N204 drops, and the forward reaction slows down. Conversely, the partial pressure of N02 increases, so the rate of the reverse reaction increases. Soon these rates become equal. A dynamic equilibrium has been established. 

We perceive this lower energy as a cooler temperature, meaning that the water vapour in a steam-filled bathroom will cool down conversely, the mirror (and walls) become warmer as they receive the energy that was previously possessed by the steam. These changes in the temperatures of gas and mirror occur in a complementary sense, so no energy is gained or lost. 

The simulation discussed above was based on full color produced by individual red, green, and blue emitters. Other full-color reproduction approaches have been proposed for OLED displays including color from blue emitter by means of energy down conversion fluorescent filter [177], and color from white emitters by means of transmission color filter sets similar to that used in LCD industry [178,179]. Table 1.5 compares the EL efficiency of equivalent white... 

For second harmonic generation (SHG), the tensor is y(2)(—2co co, co) (useful for frequency doubling and parametric down-conversion) while for the linear electrooptic or Pockels71 effect the tensor is y(2)(— co co, 0) (useful for Q-switching of lasers, for phase or amplitude modulators, and for beam deflectors) for optical rectification the tensor is y 2>(0 00, —co) for frequency mixing the tensor is y(2)(— co3 oolr co2) (useful for frequency up-converters, optical parametric oscillators, and spectroscopy). 

Figure 4 Average energy of the nonequilibrium vibrational population distribution computed for the vibrational cascade in crystalline naphthalene in Fig. 3. At T = 0, the peak moves toward lower energy at a roughly constant rate, the vibrational velocity of 8.9 cm-1 ps. The initial 1627 cm-1 of vibrational energy is dissipated in 180 ps. The vibrational velocity is the same at 300 K. In the limit that cubic anharmonic coupling dominates [Equation (6)], increasing the temperature increases the rates of up- and down-conversion processes, but has no effect on the net downward motion of the population distribution. Although the lifetimes of individual vibrational levels will decrease with increasing temperature, VC is not very dependent on temperature in this limit. (From Ref. 5.)...

The mercury-free fluorescent lamps and plasma display panels require alternative luminescent materials for efficient conversion of ultraviolet radiation to visible light. The quantum cutting (two photon luminescence or photon-cascade emission) was demonstrated in famous "Eu -Gd " pair" containing system employing the concept of down-conversion, which means that two visible photons are emitted after... 

Up-conversion and down-conversion luminescence, scintillator materials, and photonic crystals are other topics of recent interest.Up-conversion is the ability of a material to convert low-energy excitation light into higher energy... 

Down-conversion is another useful technique that has applications in lighting and plasma flat panel displays. The process involves the input of a vacuum ultraviolet photon and the output of multiple visible photons. This down-conversion was recently reported with Eu + doped LiGdp4. Upon absorption of a high-energy photon by Gd +, two visible photons were emitted through an energy transfer between Eu + and Gd + with a quantum... 

The opposite effect, the so-called down-conversion was reported in 1974, independently, for YFsiPr [5.230, 5.231]. Here, two photons with lower energy (visible) are emitted per photon absorbed at energy above about 5.7 eV (Figure 5.52). Absorption preferably takes place in the 5d band of Pr, as the underlying 4f-5d optical transition is parity allowed (Figure 5.53). 

Such down-conversion phosphors are needed for energy efficient Hg-free lamps, which are driven by a Xe/Ne discharge. In order to establish f-f transitions with VUV-excitation and to avoid band-to-band absorption by the host lattice, large band-... 

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