Luminescence ionic radii

The luminescent centers require a range of properties that include a large cross-section for the collision excitation to occur, an ionic radius and valency to fit the lattice and be stable under the applied high electronic fields, and the capability to display high luminous efficiency when excited.11 Metal ions suitable for EL devices include Mn, Tb, Sm3+, Tm3+, Pr3+, Eu2+, and Ce3+.12-17 ZnS lattices doped with Mn2+ (yellow-orange emission at ca. 585 nm) have proved to be one of the best phosphors for EL devices. 

Minerals of tin are capable of intrinsic luminescence, possibly connected with defect centers containing Sn T The ionic radius of Sn" " is of 0.83 A and the possible substituting luminescence center is Ti" " with an ionic radius of 0.75 A. 

Ionic radii of Ba are of 1.49 A in 6-coordinated form and 1.56 A in 8-coordinated form. The main substituting luminescence centers are Bi + with an ionic radius of 1.49 A and 1.56 A in 6-coordinated and 8-coordinated forms, respectively, Ag with ionic radii of 1.29 A and 1.42 A in 6-coordinated and 8-coordinated forms, respectively, Cu with an ionic radius of 0.91 A in 6-coordinated form, Eu + with an ionic radius of 1.31 A, Ce with an ionic radius of 1.15 A and other TR +. 

Minerals of Ti are capable of intrinsic luminescence, which is connected with (TiOe) groups and a Ti + center. The ionic radius of Ti " is 0.75 A in 6-coordinated form. The possible substituting element is Cr + with an ionic radius of 0.76 A. 

The ionic radius of silicon in tetrahedral coordination is 0.4 A. The main substituting luminescence center is Fe with an ionic radius of 0.63 A in tetrahedral coordination. 

The ionic radius of aluminum in octahedral coordination is of 0.67 A. The main substituting luminescence centers are Cr " with an ionic radius of 0.75 A in octahedral coordination, Mn and Mn + with ionic radii of 0.81 and 0.67 A in octahedral coordination and and V with ionic radii of 0.93,0.78... 

The main substituting luminescence center is Mn " (ionic radius of Na" " = 1.16 A). It is interesting to note that Na bearing minerals are very often characterized by luminescence connected with S2 and O2 impurities. 

The possibility of Ni participation in minerals luminescence has not been seriously considered yet, but we are confident that it has to be done. The ionic radius of Ni " is 69 pm in tetrahedral coordination and 83 pm in the octahedral one. Thus it may substitute many cations with similar dimensions, such as Mg, Zn, Ca. 

It is interesting to note that in magmatic apatites the luminescence of uranium containing centers have not been discovered before or after oxidizing heating. Thus it is reasonable to suppose that uranium is present mainly in the 11" + form. The U with an ionic radius of 0.97 A may be located in the apatite structure instead of Ca with the ionic radius of 0.99 A. The most likely way for achieving the excess charge compensation is the Na" for Ca " structural substitutions. 

Porphyrin molecules form stable complexes with lanthanide ions, these complexes have intensive absorption in a visible range of spectrum. Erbium, ytterbium and neodymium complexes are characterized by a 4f-luminescence in near IR-range of spectrum [1]. The most studied complexes with porphyrins are ytterbium complexes since Yb has smaller ionic radius in comparison with lanthanum (radius of Yb ion is 1.01 A), which determines higher stability of these metallocomplexes. Distinctive feature of Yb porphyrin complexes is a characteristic narrow and rather intensive luminescence band located in the IR-range at 975-985 nm, in so-called therapeutic window of tissue transparency. ... 

Eu -activated conventional oxide phosphors as a function of (n x r x Ea)l%. Although the calculated emission-band positions are underestimated compared with the measured one, both the calculated and measured emission-band wavelengths are shifted to the longer-wavelength side with increasing value of (n x r x Ea)/8. This result supports that the coordination number (n) and ionic radius (r) of the cation are key factors for estimating the emission-band wavelength of Eu -activated phosphors. In addition, similar luminescence behavior is observed in the Eu -activated (oxy)nitride phosphors [85]. 

Ionic radii of zirconium are of 0.73 A in 4-coordinated form and 0.86 A in 6-coordinated form. The possible substituting luminescence centers are Ti" " with ionic radius of 0.75 A in 6-coordinated form, REE ", Cr ", Cr, Mn " and Fe ". Impurities of U and Th are also possible, which may radiatively decay with formation of radiation induced luminescence centers. 

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