f-f oscillator strengths, hypersensitivity, branching ratios and quantum efficiencies discussed in the light of forgotten results

The famous Judd's formula is briefly recalled in the simplified form that was the reason of its success. After recalling shortly some older results pointing to the role of refraction index in hypersensitivity, two of the approximations underlying the formula are discussed in reference with experimental results. It shows that the "natural excitation" approximation, though generally forgotten, is very important when using Judd's formula between excited states. The "constant denominator" approximation usually criticized is shown on the opposite not to be very detrimental when Judd's formula is considered as semi-phenomenological as it is usually the case, provided the minimizing mathematical treatment considers each oscillator strength on an equal footing. Examples taken from U4+ and Pr3+ shows that the usual three even order parameters are still adequate provided the physics behind them is not based on the f-d mixing. (C) 2004 Elsevier B.V. All rights reserved.