The absorption cross-section of 1.21at.%Nd~(3+)-doped Ca0.05Y0.95VO4 crystal was calculated as 14.11×10-20cm2 at 808nm, so the crystal was fit to be pumped by 808nm LD, and its emission cross-section and radiation lifetime were calculated as 2.771×10-18cm2 and 106.5μs respectively.

The absorption cross-section σ, radiation lifetime ττ and fluorescence quantum efficiency η are determined from the measured absorption-and fluorescence spactra. On the basis of these parameters the mode-locking properties and the laser action of these dyes are discussed.

The results indicate that, with the increase in B 2O 3 content, the radiation lifetime increases, while the spontaneous emission probability, the absorption cross-section, the corresponding integral absorption cross-section and emission cross-section all decrease, that the refraction index reaches its minimum when the mole fraction of B 2O 3 is 15%, and also that the absorption cross-section and the emission cross-section increase with the electric field intensity of the modifier cation.

Experiments on several polymers have shown that the dependence of the radiation lifetime under load on the intensity of the ultraviolet radiation and test temperature is governed by general empirical laws.

The effectiveness of the integral method of reciprocity was demonstrated in determining the stimulated emission cross sections and radiation lifetime of an ytterbium ion in the laser crystals Yb3+:KYW and Yb3+:KGW.

Based on this method, formulas for calculating the radiation lifetime of impurity centers in crystals have been derived.

This will consider the cascading of second-order nonlinearities of KTP crystal, the third-order nonlinearity of the laser medium, influences of the continuous pump rate, and the stimulated radiation lifetime of the active medium.

The maximum experimental error is 0.3 cm-1 for the energy and 20% for the radiation lifetime measurements.

For molecular gas lasers with two combined levels (including flowing type gas lasers), it is pointed out that if the short-range diffusion time is much shorter than the radiation lifetime spatial holes burned will be eliminated, and when the gas is rarefied, this condition becomes that the short-range free motion time should be much less than the radiation lifetime and more convenient criterions are given.

In this paper we discuss the spectral properties of two organic dyes: pentame-thylidyne and undecamethylidyne. The absorption cross-section σ, radiation lifetime ττ and fluorescence quantum efficiency η are determined from the measured absorption-and fluorescence spactra. On the basis of these parameters the mode-locking properties and the laser action of these dyes are discussed.

In stationary state the output power of LED can be written aswhere η is the external quantum efficiency, ηi the internal quantum efficiency, ηq, the carrier efficiency, J the injection current density, A, the radiation cross -section and e the electron charge.Using the standard power pB as normalizing treatment, we can obtain the normalized equationwhere I is the injection current, ηi,B and IB is the standard internal quantum efficiency and injection current, respectively. Owing toso we must consider simultanously...

In stationary state the output power of LED can be written aswhere η is the external quantum efficiency, ηi the internal quantum efficiency, ηq, the carrier efficiency, J the injection current density, A, the radiation cross -section and e the electron charge.Using the standard power pB as normalizing treatment, we can obtain the normalized equationwhere I is the injection current, ηi,B and IB is the standard internal quantum efficiency and injection current, respectively. Owing toso we must consider simultanously the influence of the carrier lifetime τ and the radiation lifetime τr.According to the literature [12], large trapping cross-section and high deep level impurity concentration exist in InGaAsP, so the effect of mul-tiphonon recombination relating to the deep level impurity (or trap) must be considered. From this, the T may not only be influenced by the Auger recombination lifetime τA, the surface recombination lifetime τ,the radiation recombination lifetime τr, but also by the multiphonon recombination lifetime τp. Thus T can be written aswhere s is the recombination rate at the interface, d is the active layer thickness.Hence, the total recombination rate is expressed aswherewhere A, Bp and Br are the Auger, multiphonon and radiation recombination coefficient, respectively; n, is the injection carrier density, pb, the acceptor concentration in equilibrium, and N, the concentration of the deep level impurity.Based on the above mentioned expressions, we can obtain the following equationFrom above, the effect of the deep level impurity on the output power saturation in InGaAsP/InP LED can be obtained. This influence has been verified both experimentally and theoretically (Fig.6) , hence, it is not sufficient to consider only the effect of the Auger recombination.In this paper, the dependences of the deep level impurity (or trap) on the injection current, the carrier lifetime and the output power are discussed (see the Fig.1,2 and 4 ).The effect of temerature T on η; is also shown as in Fig.3.From Fig.l, we can see the deviation degree from the I-P linear dependence △pD sharply increases with increasing Nt and as the Nt decreases,the T increases at the same I in Fig. 2 . At N, = 1.5×1014cm -3,the calculated τ value well agrees with the experimental one[14] .Thus it can be seen that it is necessary to reduce the deep level impurity concentration in InGaAsP.Fig. 3 shows that η; is inversely proportional to T at the same I, and when the I is greater than 200mA, the ηi; hardly changes with I at the same T, therefore, the influence of temperature must be considered in range of I = 10-200mA. From Fig. 5, it may be shown that multiphonon recombination coefficient B, sharply increases with εT at the same T, but when the εT is greater than 0.5eV the B, hardly changes with T, when εT is less than 0.35eV the multiphonon trapping cross-section is much less than 10~20cm2, where the multiphonon recombination can't be considered by calculation. In general, because εT is no larger than 0.3eV in GaAlAs LED, its property is better than InGaAsP LED.Hence, these phenomenon further illustrate that reducing the N, or removing the deep centre is very important for improving the characteristics of InGaAsP LED and laser.