Quantum cutting

Neodymium systems have the potential for quantum cutting because Nd3+ has a high lying 4f" state, 2G(2)9/2, at about 47 000 cm-1, which has a 7000 cm-1 gap above the next lower level, 2F(2)7/2 (Camall et al., 1988). This energy gap is sufficient to prevent non-radiative relaxation between the two states, and emission from the 2G(2)y/2 state can be expected. Exciting the 2G(2)9/2 state directly is impractical, due to the very low transition probability from the ground state. However, if efficient absorption into the 5d band occurs, then the 2G(2)9/2 state may be populated via non-radiative phonon-assisted relaxation, resulting in 2G(2)9/2 emission. 

By far, the most studied quantum cutting system to date is for praseodymium, where the 4f2 1 So state lies below the lowest 5d state for many fluorides and some oxides. For most Pr3+ doped systems, the nephelauxetic effect and the 5d crystal field splitting are large enough to push the lowest 5d level below the 1 So state. However, for those systems in which the So... 

Fig. 10. Energy level scheme of Pr3"1" showing the 4f2 levels and two possibilities for the position of the 4f5d levels (Oskam et al., 2002). On the left the lowest 4f5d level is above the 1 Sq level making quantum cutting from the 1 So level possible. On the right the 4f5d level is situated below the 1 Sq level and fast UV 4f5d emission to the lower 4f2 levels is possible potentially being a good scintillator or UV laser materials.

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... 

The emitted photons are located in the blue and red spectral region of the spectrum, respectively. In 1999, a first example of a quantum cutting material with two visible photons at similar wavelength (in the red spectral region), was presented LiGdp4 Fu (Figure 5.54) [5.232]. 

The reverse of upconversion is downconversion, where each quantum of (vacuum) ultraviolet radiation is converted to several quanta of infrared or visible radiation (quantum cutting) [386]. For example, the highest energy emission for the excitation of Cs2LiTmCl6 Nd31 by 476.9 nm radiation is below ca. 11,300 cm-1, since the cross-relaxation of 4G4 Tm3+ level leads to the excitation of Tm3+ 3H5 and Nd3+ 4F3/2 [344]. 

State lies below the lowest 5d level, Pr + provides a nearly ideal system for quantum cutting for the following reasons ... 

Van der Ende, B.M., Aarts, L., Meijerink, A., 2009. Near-infrared quantum cutting for... 

Fig. 18 Various quantum cutting schemes. Ions A and B are lanthanide ions. B1, B2 represent two B ions. Upward arrows represent exeitation dotted arrows represent cross-relaxation processes thick downward arrows represent emission (adapted from [161])...

The lanthanide ion Er has many luminescent levels and rather than quantum cutting, it is photon cascade downconversion that occurs upon high energy excitation [166, 167]. 

Several quantum cutting regimes have been utilized with most of them involving Gd " and Pr " since these ions have high energy levels from which the initial photon is released. However, these levels lie too high for effective absorption of solar energy. The emission from Yb " is just above the band gap of crystalline Si. Hence, the downconversion in which one blue photon ( 483 nm) is absorbed by Tb " and used to sensitize two Yb " ions for Vs/2 emission near 1 pm has... 

Wegh RT, Donker H, Oskam KD, Meijerink A (1999) Visible quantum cutting in LiGdF4 Eu " through downconversion. Science 283 663-666... 

Xiong F, Lin Y, Chen Y, Luo Z, Ma E, Huang Y (2006) Visible quantum cutting in Pi PbW04 crystal through energy transfer between the host and Pt ions. Chem Phys Lett 429 410-414 Vink AP, Dorenbos P, van Eijk CWE (2003) Obstavation of the photon cascade canission process under 4f 5d and host excitation in several Pr -doped materials. J Solid State Chem 171 308-312... 

Zhang QY, Huang XY (2010) Recent progress in quantum cutting phosphors. Progr Mater Sci 55 353 27... 

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