P.J. Alonso

Excitation spectra and fluorescent lifetime measurements of Mn2+ in CaF2 and CdF2

Abstract The excitation spectrum of the Mn 2+ emission has been measured in CaF 2 and CdF 2 . The observed excitation bands have been assigned to transitions of the Mn 2+ ions in a cubic environment. The calculated values for the crystal field ( Dq ) and Racah parameters ( B,C ) are Dq = 425 cm -1 for CaF 2 , Dq = 500 cm -1 for CdF 2 and, B = 770 cm -1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level 4 T 1g ( 4 G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn 2+ ions.

Spectroscopic properties of Cr3+ In RbCdF3

A spectroscopic study of chromium-doped RbCdF3 crystals has been performed. Cubic, tetragonal and trigonal Cr3+ centres have been detected by EPR measurements. The spin Hamiltonian parameters of trigonal and one type of tetragonal Cr3+ ions, not previously reported, have been found to be: g/sub ///=1.969, gperpendicular to =1.971 and mod D mod =0.1576 cm-1 for the trigonal centre and g/sub ///=1.970, gperpendicular to =1.972 and mod D mod =0.0722 cm-1 for the tetragonal one. Crystal field and Racah parameters of cubic Cr3+ derived from the optical absorption spectrum are: Dq=1420 cm-1, B=800 cm-1 and C=3290 cm-1. Photoluminescence has been measured at different temperatures and the phonon structure observed at 15 K has been associated with different Cr3+ centres. The lifetimes of the emitting levels of cubic and trigonal Cr3+ ions measured at 15 K have been found to be 470 mu s and 220 mu s respectively. At 300 K the lifetime of cubic centres decreases to about 180 mu s. No direct influence of the phase transition on the optical properties of Cr3+ ions, when the authors go through the transition temperature, has been detected.

Thermoluminescence of 3d-ions doped CaF2

Abstract Thermoluminescence measurements of 80 K X-irradiated CaF 2 : Me (Me: Mn, Co, Ni) are reported. The spectral distributions of the glow peaks coincide with those of the X-ray excited luminescence. It has been previously attributed to Me 2+ emission. The temperatures, activation energies and order of the kinetics for each peak are reported. They do not depend on the dopant and are the same as those given by other authors for the glow peaks in 80 K X-irradiated CaF 2 : RE. The observed emission is attributed to the de-excitation of Me 2+ formed in an excited state by recombination of released holes with Me + formed during low temperature X-irradiation. A similar mechanism has been proposed to explain the TL measurements in CaF 2 : RE.

Luminescence in x-irradiated CaF2:Co

Abstract Photoluminescence of X-irradiated CaF 2 :Co single crystals is reported. The emission spectrum shows four peaks at 505, 550, 640 and 685 nm, all of them with an excitation band at 275 nm. The same emission spectrum, plus a band at 280 nm, is found in X-ray excited luminescence measurements. Thermoluminescence of 80 K X-irradiated crystals gives a glow curve with five peaks at 100, 125, 145, 190 and 225 K. The spectral distribution of these glow peaks is similar to that of the X-ray excited luminescence. The 280 nm band is associated with electron—hole recombination. The other four bands are associated with electron transitions among excited states of Co 2+ produced by recombination of holes and Co + -ions created by X-irradiation.

Photoluminescence of Ni2+ ions in RbCdF3 and RbCaF3

Abstract The optical properties of nickel doped RbCdF 3 and RbCaF 3 crystals have been studied. Absorption bands at about 440, 500, 670, 880 and 1500 nm have been found. They can be associated with Ni 2+ ions in an octahedral environment with 10 Dq = 6600 cm −1 , B = 950 cm −1 and C = 4000 cm −1 . Photoluminescence has been detected at 530 and 750 nm in both crystals. An infrared emission at 1800 nm was also found in RbCdF 3 while it was too weak to be measured in RbCaF 3 . The lifetimes of these emissions have been obtained as a function of temperature and the results analysed using the Struck-Fonger model of thermal quenching. Concentration quenching has also been studied. Going from 0.1% to 0.5% in the nickel content produces decrease of the lifetime of the 530 and 750 nm emissions while that of 1800 nm emission does not change.

Charge change processes of 3d-ions in doped SrF2

Thermoluminescence measurements of LNT X-irradiated pure SrF2 and SrF2 : Me (Me = Mn, Co, Ni) are reported. The temperature and the activation energies for each glow peak are given. They do not depend on the dopant. In pure SrF2 the emission of the glow peaks consists of the intrinsic emission (300 nm). In doped crystals the spectral distributions of the glow peaks coincide with those of the X-ray excited luminescence. The observed emission bands are attributed to the de-exciting of Me2+ ions created in an excited state by the recombination of released holes with the Me+ centres formed by low-temperature irradiation.

Luminescence of Ni doped CaF2

Abstract Luminescence measurements of CaF2 : Ni are reported. Before X-irradiation an emission band at 680 nm is observed with the corresponding excitation band at 255 nm. After RT X-irradiation the emission spectrum consists of three peaks at 290, 375 and 680 nm, all of them with an excitation band at 255 nm. The same emission spectrum together with the electron-hole recombination band is obtained by X-ray excitation. A comparison with previous EPR and optical absorption measurements indicates that the emission bands are due to different kinds of Ni2+ centers. The emission processes are similar to those found in CaF2 : Co and CaF2 : Mn.

An EPR study of Ni+ centers in SrF2:Ni and BaF2:Ni

Abstract An EPR study of RT X-irradiated SrF2:Ni and BaF2:Ni has been performed. Different kinds of Ni+ centers showing small deviations with respect to a basic structure have been observed. This basic structure consists of a Ni+ ion displaced along a direction from the cation substitutional position toward the center of a face of the cube of fluorines. These results are similar to those previously reported on CaF2:Ni. The spin Hamiltonian parameters of the different centers obtained from the analysis of the corresponding rotational diagrams are also reported.

Radiation-induction Ni+centres in BaF2:Ni

Ni+ centres produced by room temperature X-irradiation of BaF2:Ni crystals have been studied by optical and EPR techniques. An absorption band at about 390 nm and an orthorhombic EPR signal (gx=2.094(5), gy=2.103(5) and gz=2.693(5)) showing a structure characteristic of a superhyperfine interaction with four fluorine ions have been associated with the Ni+ defects. A basic model consisting of a Ni+ ion displaced from the Ba2+ substitutional position towards the centre of one of the faces of the cube of fluorines is proposed for these Ni+ defects. The results are similar to those previously reported in X-irradiated CaF2:Ni and SrF2:Ni.

Ni2+ emission in SrF2

Abstract Luminescence measurements of X-irradiated SrF 2 :Ni are reported. After X-irradiation two emission bands have been found. One of them peaked at 293 nm and has an excitation band at 267 nm. The other one at about 770 nm, which is much weaker, has an excitation band at 274 nm. Both emission bands are also observed under X-ray excitation. A comparison with some previous studies of the absorption and thermoluminescence properties of X-irradiated SrF 2 :Ni indicates that the emission bands are due to two different kinds of Ni 2+ centers. The proposed emission mechanisms are similar to those found in CaF 2 :Ni.