A.P. Vink

VUV excitation and 1S0 emission of Pr3+ in BaSiF6 and selecting host lattices with 1S0 Pr3+ emission

Abstract We have studied the luminescence characteristics of Pr3+ in BaSiF6 powder samples co-doped with K+ in the 60– 800 nm range at room and liquid He temperature. After excitation in the 4f5d configuration of Pr3+, emission from the 1 S 0 state is observed but no 4f5d→4f2 emission. The 1 S 0 state is measured in excitation spectra as a weak line about 6200 cm −1 below the maximum of the lowest energy 4f5d crystal field state. Emission from the 3 P 0 and 1 D 2 multiplets is almost completely quenched which is not yet fully understood. Under band-to-band ( 11.7 eV or higher energy) excitation at 12 K , we observe excitonic emission, peaking at 327 nm , which is quenched at room temperature. A reliable prediction can be made whether 1 S 0 emission of Pr3+ can be expected in a host lattice. It is based on the 4fn→4fn−15d excitation energy of other trivalent lanthanides or on the 4f7→4f65d excitation energy of Eu2+ in the same host lattice. It also appears that when 6 P 7/2 line emission of Eu2+ is observed, 1 S 0 emission of Pr3+ can be expected. A list of host lattices is presented for which 1 S 0 emission is expected when doped with Pr3+.

Luminescence excitation study of the higher energy states of Pr3+ and Mn2+ in SrAlF5, CaAlF5, and NaMgF3

The possibility to use Mn2+ co-doping to modify the emission properties of Pr3+-based quantum cutting phosphors—i.e., phosphors that emit one UV and one visible photon for each absorbed vacuum UV (VUV) photon—into phosphors that emit two visible photons, was studied experimentally. In this respect a luminescence excitation study, using synchrotron radiation, between 500 and 50 nm of Pr3+ and Mn2+ impurities in SrAlF5, CaAlF5, and NaMgF3 was performed. Excitation of Pr3+ into the 4f5d excited states results in emission of UV photons from the 1S0 state followed by visible photons from the 3P0 state with an internal quantum efficiency exceeding 100%. It was found that a favorable overlap between the 1S0→1I6 Pr3+ emission and the 6A1→4Eg, 4A1g Mn2+ absorption exists that should promote energy transfer from Pr3+ to Mn2+. However no such energy transfer could be observed in SrAlF5. At higher excitation energies (>7 eV) intense structured Mn2+ excitation bands are found that are assigned to 3d5→3d44s transitions...

Observation of the photon cascade emission process under 4f15d1 and host excitation in several Pr3+-doped materials

Abstract An overview is given of the research on the photon cascade emission (PCE) process for different Pr3+-doped materials. The factors which determine the amount of emission originating from the second ( 3 P 0 / 1 D 2 → 2S+1 L J ) quantum cutting step are discussed and results on Pr3+-doped hosts which show both the PCE process and parity-allowed 4f 1 5d 1 → 2S+1 L J emission are reported. Lastly, the PCE process under host excitation with X-rays is discussed.

Ce3+ and Pr3+5d-energy levels in the (pseudo) perovskites KMgF3 and NaMgF3

Abstract The location of the 5d-energy levels of Ce 3+ and Pr 3+ in the cubic perovskite KMgF 3 and in the distorted perovskite NaMgF 3 was determined from spectroscopic studies in the vacuum ultraviolet. It is established that Ce 3+ and Pr 3+ ions both occupy the same site in each host: K + sites for KMgF 3 and Na + sites for NaMgF 3 . The small crystal field splitting and the small value of the centroid shift of the 4f n −1 5d-configuration yield a relatively high energy for the lowest 5d state of both Ce 3+ and Pr 3+ . The lowest 5d state of Pr 3+ in both hosts is found at energy higher than the 4f 2 1 S 0 state, enabling the photon cascade emission to occur.

The observation of photon cascade emission in Pr3+-doped compounds under X-ray excitation

Abstract The problem of obtaining two visible photons from a single incident vacuum ultraviolet photon is considered and conditions of cascade emission observation in various Pr 3+ -activated compounds are reviewed. Hosts with weak crystal field, low phonon energies, large band gap, large cation–anion distance, and large coordination number for the substitution site are desirable. Emission spectra and decay curves under X-ray excitation of some Pr 3+ -doped materials: LaAlO 3 , LaMgAl 11 O 19 , SrAl 12 O 19 and SrAlF 5 have been measured. Photon cascade emission has been observed in SrAl 12 O 19 :Pr 3+ and SrAlF 5 :Pr 3+ . The influence of the Pr 3+ concentration on the emission has been studied in SrAl 12 O 19 :Pr 3+ . Intrinsic (excitonic) luminescence, which has an adverse effect on the cascade emission, is usually suppressed in compounds containing 0.5 or more percent of Pr 3+ .

Luminescent properties of Ce3+ in MSO4 (M: Ca, Sr and Ba) and the effect of Na+ co-doping

Abstract The optical properties of Ce 3+ in CaSO 4 , SrSO 4 and BaSO 4 are reported. The Ce 3+ ion shows 4 f 0 5 d 1 → 2 F 5/2 , 2 F 7/2 luminescence in all three sulphates. Co-doping with Na + does not change the local surrounding of the Ce 3+ ion, but enhances the amount of Ce 3+ ions built in. Under optical excitation, besides the typical Ce 3+ doublet emission in the ultraviolet spectral region, band emission around 445 nm was observed. This band emission was not assigned to emission from a Ce 3+ centre, but to emission from an impurity-trapped exciton. Under X-ray excitation, both Ce 3+ emission and an emission band around 380 nm was observed. This band was assigned to emission from a self-trapped exciton.

Opposite parity 4fn-15d1 states of Ce3+ and Pr3+ in MSO4 (M=Ca, Sr, Ba)

Abstract Research on Ce 3+ and Pr 3+ in three different sulphate lattices reveal strong similarities regarding the 4f n −1 5d 1 level structure. The energy difference between the 4f 0 5d 1 levels of Ce 3+ and the 4f 1 5d 1 levels of Pr 3+ is in good approximation a constant value of 12 240±750 cm −1 . The crystal field splitting of the 4f n −1 5d 1 levels for Ce 3+ and Pr 3+ , doped in the same sulphate host, is comparable. The first 4f 1 5d 1 band of CaSO 4 :Pr 3+ is split in at least three levels. This is ascribed to splitting due to the spin–orbit interaction of the remaining electron in the 4f shell and to the electrostatic interaction between the 4f and the 5d electron.