U. Caldiño

Optical spectroscopy of zinc metaphosphate glasses activated by Ce3+ and Tb3+ ions

The photoluminescence of Ce3+ and Tb3+ ions in zinc metaphosphate glasses is investigated. The blue and green emissions of Tb3+ ions are enhanced upon UV excitation through energy transfer from Ce3+ to Tb3+ ions. The efficiency of such an energy transfer was estimated based on spectroscopic data and resulted in being about 20?23%. Spectroscopic data revealed that the energy transfer occurs via a non-radiative process inside Ce3+?Tb3+ clusters formed in the glass. This ion clustering could be useful for the design of efficient conversion phosphors of ultraviolet to blue and green light.

Photoluminescence of Ce3+ and Mn2+ in zinc metaphosphate glasses

The spectroscopic characterization of zinc metaphosphate glasses, singly and doubly doped with Ce3+ and Mn2+ ions, is performed through excitation and emission spectra and decay time measurements. The weak yellow emission of Mn2+ is significantly enhanced by means of an efficient energy transfer from Ce3+ to Mn2+ ions. The efficiency of the energy transfer has been estimated based on spectroscopic data, and turned out to be about 53%. From spectroscopic data it can also be inferred that the energy transfer is nonradiative in nature and it takes place between Ce3+ and Mn2+ clusters formed in the glass through a short-range interaction mechanism. This impurity clustering appears to be a relevant finding for the design of efficient conversion phosphors of ultraviolet to visible light.

Blue–green–red luminescence from CeCl3- and MnCl2-doped hafnium oxide layers prepared by ultrasonic spray pyrolysis

Hafnium oxide films doped with CeCl3 and/or MnCl2, and deposited at 300 °C by an ultrasonic spray pyrolysis process, were characterized using x-ray diffraction (XRD), energy-dispersive spectroscopy and photoluminescence. The XRD results revealed that the films are predominantly amorphous. The weak green–red emission of Mn2+ is enhanced through an efficient energy transfer from Ce3+ to Mn2+ ions. Spectroscopic data revealed that the energy transfer is nonradiative in nature and it could occur in Ce3+ and Mn2+ clusters through a short-range interaction mechanism. The efficiency of this transfer increases with the Mn2+ ion concentration, so that an efficiency of about 78% is attained for a 5 at.% of MnCl2 concentration, which makes these films interesting phosphors for the design of luminescent layers with blue, green and red emissions.

Spectroscopic characterization of Er3+ transitions in Bi4Si3O12

A systematic investigation of optical absorption and luminescence is presented for Er3+ ions in the Bi4Si3O12 crystal. The intrinsic emission of this crystal gives rise to a radiative energy transfer among the host lattice and Er3+ ions. Measured oscillator strengths for seven different transitions from the ground state to excited state manifolds compare favourably with the electric dipole oscillator strengths calculated from the Judd?Ofelt formalism. Radiative lifetimes of the former seven excited states were determined from calculated spontaneous emission probabilities. The ratio of the excited state absorption oscillator strength to the ground state absorption oscillator strength turned out to be similar to those found for materials pumped efficiently at 4I11/2 level excitation wavelengths. The stimulated emission cross section and gain spectra were determined for the transition of special interest for laser application.

Crystal field analysis of Nd3+ energy levels in monoclinic NdAl3(BO3)4 laser

The energies of 135 Kramers doublets extending up to the 2H111/2 multiplet for Nd3+ in a monoclinic C2/c space group (No 15) NdAl3(BO3)4 (NAB) single crystal laser have been determined from polarized optical absorption and photoluminescence measurements at 7 K. The strongly polarized character of the Nd spectra has been discussed under the assumption of a local D3 symmetry, higher than the C2 symmetry of NAB, and the observed energy levels have been labelled with the adequate crystal quantum numbers and irreducible representations. A detailed Hamiltonian of 21 parameters has been used in the simulation of the energy levels and associated wavefunctions of the 4f3 configuration of Nd3+. The diagonalized complete energy matrix combines simultaneously the free-ion and single-particle crystal field interactions. Starting Bkq CF parameters were calculated from the semi-empirical simple overlap model SOM. A comparative simulation considering the C2 symmetry of NAB is provided. Moreover, two-electron CF interactions as well as an empirical correction have been tested in calculating the anomalous splitting of the 2H211/2 levels. A final fit in D3 symmetry produces a very good adjustment with a low rms deviation σ = 15.3 cm-1 between observed and calculated energy levels.

Influence of neodymium concentration on the cw laser properties of Nd doped Ca3Ga2Ge3O12 laser garnet crystal

Spectral and laser properties of Nd3+ doped Ca3Ga2Ge3O12 have been investigated for different Nd concentrations ranging from 0.1 to 16 at %. The 4F3/2→4I11/2 emission spectrum is dominated by two main peaks at 1060 and 1065 nm whose stimulated emission cross sections change with Nd concentration. For concentrations above 0.5% luminescence quenching begins. Then, continuous wave laser gain experiments have been used to investigate the influence of these effects on the laser properties. The different factors (crystal losses and saturation intensity factor) contributing to the increase observed in the laser pump threshold with Nd concentration are discussed. Analysis of the laser spectra shows a double laser oscillation around 1060 and 1065 nm, which tends to disappear for high Nd concentrations.

Blue and red photoluminescence from Al2O3:Ce3+:Mn2+ films deposited by spray pyrolysis

Al2O3:Ce3+:Mn2+ films deposited by the spray pyrolysis technique show blue and red emissions under ultraviolet light excitation. The blue emission is due to the de-excitation of Ce3+ ions from their excited state 5d to the split ground state 2F. The usually weak red emission attributed to 3d??3d de-excitation of Mn2+ is enhanced through an efficient energy transfer from Ce3+ to Mn2+ ions. The most probable mechanism of energy transfer is found to be electric dipole?quadrupole interaction. The quantum efficiency of this transfer was estimated as being near to 100%, which makes these films interesting phosphors for the design of luminescent layers in flat-panel displays with two-colour emission.

Stimulated emission, excited state absorption, and laser modeling of the Nd3+:Ca3Ga2Ge3O12 laser system

We report on a full spectroscopic characterization of the Nd3+ ion doped Ca3Ga2Ge3O12 garnet laser host for different ion concentrations ranging from 2.5×10−2 up to 2 at. %. The Judd–Ofelt formalism has been applied, from which the stimulated emission cross section corresponding to the 4F3/2→4I11/2 laser channel has been determined. Excited state absorption cross section in the 1020–1090 nm region has been measured by using two beam spectroscopy, demonstrating that the 1060 and 1065 nm laser emissions are not affected by excited state absorptions. Finally, once the basic parameters are known, we have applied the mode overlap formalism in order to determine the Nd3+ concentration and crystal length which optimize the laser performance of an end diode pumped laser system. We have concluded that the maximum output power is reached when the Nd3+ concentration and crystal length are around 0.75 at. % and 0.6 mm, respectively

Luminescence of Rare Earth Ions in Strontium Barium Niobate Around the Phase Transition : The Case of Tm3+ Ions

The photoluminescence of ferroelectric Sr 0.6 Ba 0.4 (NbO 3 ) 2 congruent crystals doped with four different trivalent rare earth ions, Nd 3+ , Eu 3+ , Tm 3+ and Yb 3+ , has been examined in the temperature range around the Curie temperature, when the system undergoes the transition to the paraelectric phase. While the luminescence of large ions is not sensitive (Nd 3+ ) or weakly sensitive (Eu 3+ ) to the phase transition, that of small ions (Tm 3 + and Yb 3 + ) is highly sensitive to temperature changes around the Curie temperature. Particular emphasis is given to the Sr 0.6 Ba 0.4 (NbO 3 ) 2 :Tm 3 + system, for which the luminescence spectra around the phase transition and low temperature laser site selective spectra are systematically investigated. The different spectral sensitivity of the rare earth ions to the phase transition is interpreted in terms of the lattice sites occupied by the different rare earth ions in the Strontium Barium Niobate crystal host.

Optical spectroscopy of Dy3+ ions in LiNbO3

Abstract A systematic spectroscopic study of Dy3+ doped LiNbO3 is presented. The energy position of the Stark levels and their symmetry character is given for most of the multiplets. Luminescence of this system has been investigated in the visible and infrared. The only emitting state in this region is the metastable 4 F 9 2 multiplet whose life time is temperature independent and with a value of 186 μs. Evidence about Dy3+ multicentres is also discussed.