Quantum efficiency of luminescence

The importance of transparent glass-ceramics doped by Cr as potential new materials for luminescent solar concentrators and tunable lasers is considerable It has been shown that Cr(III) exhibits exceptionally high quantum efficiency of luminescence in these materials as compared to glasses of the same compositions . Cr is also used as a probe for nucleation of and crystallization of cordierite into glass-ceramics . ... 

Quantum Efficiency Of Luminescence The intensity of luminescence can be expressed as the quantum efficiency (), which is the ratio of the amount of light emitted to the amount of light absorbed. It can also be expressed as the ratio of the rate of luminescence to the sum of all rates that deactivate the excited state. 

Absorption, emission and excitation spectra und quantum efficiencies of luminescence of lead in germanate, borate and phosphate glasses were obtained by Reisfeld and Lieblich (69). Excitation and emission spectra of lead in various glasses is presented in Fig. 8 and spectral data in Table 4. 

Figure 7 Self-atsorption probabilities for rhodamine-575 This shows a juxtaposition of predicted self-absorption probabilities for three measurement methods spectral overlap convolution (solid), emission depolarization (boxes), and time-resolved spectra (bars). The second two techniques are plotted assuming the quantum efficiency of luminescence is one.

Due to the high accuracy possible with photon counting measurements of the lifetime, this technique yields the most accurate measurement of any technique we have studied of the product nr, the quantum efficiency of luminescence and the self—absorption probability, for low rates of self-absorption. 

The emission yield f/tj defines the quantum efficiency of luminescence the ratio of the number of emitted and absorbed photons (0emission yield can indicate quenching and other photophysical and chemical processes occurring with the luminophore. 

Rohwer, L. S. Martin, J. E. Measuring the absolute quantum efficiency of luminescent materials. J. Luminesc. 2005,115,77-90. 

Nonradiative Decay. To have technical importance, a luminescent material should have a high efficiency for conversion of the excitation to visible light. Photoluminescent phosphors for use in fluorescent lamps usually have a quantum efficiency of greater than 0.75. AH the exciting quanta would be reemitted as visible light if there were no nonradiative losses. 

Recent work with multi-layer polymer LEDs has achieved impressive results and highlights the importance of multi-layer structures [46]. Single-layer, two-layer and three-layer devices were fabricated using a soluble PPV-based polymer as the luminescent layer. The external quantum efficiencies of the single-layer, two-layer, and three-layer devices were 0.08%, 0.55%, and 1%, respectively, with luminous efficiencies of about 0.5 hn/W, 3 lm/W, and 6 lm/W. These results clearly demonstrate improvement in the recombination current because of the increase in quantum efficiency. The corresponding increase in luminous efficiency demonstrates that the improvement in recombination efficiency was achieved without a significant increase in the operating bias. 

In electroluminescence devices (LEDs) ionized traps form space charges, which govern the charge carrier injection from metal electrodes into the active material [21]. The same states that trap charge carriers may also act as a recombination center for the non-radiative decay of excitons. Therefore, the luminescence efficiency as well as charge earner transport in LEDs are influenced by traps. Both factors determine the quantum efficiency of LEDs. 

A critical parameter in determining the operating efficiency of polymer LEDs is the luminescence quantum efficiency of singlet excilons in the polymer i.e. the probability that a singlet exciton will decay radiatively. The luminescence quantum elft-... 

Johnson, F. H., et al. (1962). Quantum efficiency of Cypridina luminescence, with a note on that of Aequorea. J. Cell. Comp. Pbysiol. 60 85-104. 

Griseofulvin exhibits both fluorescence and luminescence. A report by Neely et al., (7) gives corrected fluorescence excitation (max. 295 nm) and emission (max. 420 nm) spectra, values for quantum efficiency of fluorescence (0.108) calculated fluorescence lifetime (0.663 nsec) and phosphorescence decay time (0.11 sec.). The fluorescence excitation and emission spectra are given in Figure 7. 

J. N. Demas and G. A. Crosby, Quantum efficiencies of transition metal complexes. II. Charge transfer luminescences, /. Am. Chem. 93, 2841-2847 (1971). 

EXAMPLE 1.5 The sensitivity of luminescence. Consider a photoluminescence experiment in which the excitation source provides a power of 100 ptW at a wavelength of400 nm. The phosphor sample can absorb light at this wavelength and emit light with a quantum efficiency of r] = O.I. Assuming that kg = 10 fii.e., only one-thousandth of the emitted light reaches the detector) and a minimum detectable intensity of l(f photons per second, determine the minimum optical density that can be detected by luminescence. 

Eigure 5.41 summarizes the temperature behavior of decay time and quantum efficiency of red benitoite luminescence at 660 nm in the forms ln(r) and ln(q) as a functions of 1/T. In such case the luminescence may be explained using simple scheme of two levels, namely excited and ground ones. The relative quantum yield (q) and decay time (r) of the red emission may be described by simple Arhenius equations ... 

Halverson et al. examined the fluorescent lifetimes and quantum efficiencies of a very large number of compounds. Their data on the luminescence of various europium chelates and synergic agent complexes demonstrates the efficacy of the sheath. 

When a luminescence spectrum is obtained on an instrument such as that used to produce the spectra in Figure 7.23, it will depend on the characteristics of the emission monochromator and the detector. The transmission of the monochromator and the quantum efficiency of the detector are both wavelength dependent and these would yield only an instrumental spectrum. Correction is made by reference to some absolute spectra. Comparison of the absolute and instrumental spectra then yields the correction function which is stored in a computer memory and can be used to multiply automatically new instrumental spectra to obtain the corrected spectra. The calibration must of course be repeated if the monochromator or the detector is changed. 

Casey and Buehler have shown that the surface recombination velocity of n-InP ( 5xl017 carriers/cm3) is low, 103cm/sec.17 Suzuki and Ogawa have recently reported a sequence of surface treatments that cause substantial changes in the surface recombination velocity of InP.18 They found that in freshly vacuum cleaved (110) faces v, is much greater than at air exposed faces and that the quantum efficiency of band gap luminescence increases by an order of magnitude when the freshly cleaved face is exposed to air. This suggests that the surface recombination velocity is reduced when 02 is chemisorbed. 

It is possible to alter the intrinsic properties of materials by chemical nanocoating, which cannot be achieved by conventional methods. Generally the core-shell nanostructures are divided into two categories (1) lanthanides doped in the core (2) lanthanides doped in the shell. The former are synthesized in order to improve the quantum efficiency of lanthanide ions or design bio-labels, while the latter are meant for the study of surface modifications on the lanthanide luminescence or the synthesis of lanthanide-doped hollow nanospheres. 

The /3-diketonate [Nd(dbm)3bath] (see figs. 41 and 117) has a photoluminescence quantum efficiency of 0.33% in dmso-7r, solution at a 1 mM concentration. It has been introduced as the active 20-nm thick layer into an OLED having an ITO electrode with a sheet resistance of 40 il cm-2, TPD as hole transporting layer with a thickness of 40 nm, and bathocuproine (BCP) (40 nm) as the electron injection and transporting layer (see fig. 117). The electroluminescence spectrum is identical to the photoluminescence emission the luminescence intensity at 1.07 pm versus current density curve deviates from linearity from approximately 10 mA cm-2 on, due to triplet-triplet annihilation. Near-IR electroluminescent efficiency <2el has been determined by comparison with [Eu(dbm)3bath] for which the total photoluminescence quantum yield in dmso-tig at a concentration of 1 mM is Dpi, = 6% upon ligand excitation, while its external electroluminescence efficiency is 0.14% (3.2 cdm-2 at 1 mAcm-2) ... 

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