J.L. Sommerdijk

Two photon luminescence with ultraviolet excitation of trivalent praseodymium

Abstract In the fluorides YF 3 and α-NaYF 4 , the trivalent praseodymium ion shows a two photon luminescence in which one ultraviolet photon (⋍210 nm) is converted into two visible photons.

Cerium and terbium luminescence in LaMgAl11O19

Abstract Under 254 nm excitation LaMgAl 11 O 19 : Ce 3+ shows emission peaking between 340 and 360 nm with a quantum efficiency up to 65%, which is almost independent of the Ce 3+ concentration. Energy transfer between the Ce 3+ ions is not efficient. In CeMgAl 11 O 19 : Tb 3+ efficient energy transfer occurs from Ce 3+ to Tb 3+ , resulting in a green emission with a quantum efficiency up to 65%. The Ce 3+ - Tb 3+ energy transfer is ascribed to electric dipole-quadrupole interaction.

Luminescence of Pr3+-Activated fluorides

Abstract The strong dependence of the emission spectrum of YF 3 :Pr 3+ on excitation source (228.8 nm, 213.9 nm or cathode rays) is ascribed to two different types of Pr 3+ sites: one with a relatively strong crystal field and the other with a relatively weak crystal field. The presence of the latter is connected with the conversion of one short-wave UV (≲ 215 nm) photon into two visible photons. Two-photon luminescence of Pr 3+ was also found for α-NaYF 4 and LaF 3 , but not for CaF 2 and BaF 2 due to the too strong crystal field in these lattices. The occurrence of two-photon Pr 3+ luminescence is compared with the intensity of the IR-excited green emission of the corresponding Yb 3+ , Er 3+ -activated lattices. The intensity of the Pr 3+ luminescence at shortwave UV excitation (213.9 nm) is rather weak. Luminescence of reasonable efficiency is, however, observed on excitation with cathode rays.

Luminescence of MeFX : Eu2+ (Me = Sr, Ba; X = Cl, Br)

Abstract Compounds of the type MeFX : Eu 2+ with Me = Sr , Ba and X = C 1, Br are efficient phosphors. Emission consists of both a 5d-4f band as well as 4f-4f lines, their relative intensities being strongly dependent on host lattice and temperature.

On the Efficiency of Yb3+‐Er3+ Activated Up‐Conversion Phosphors

Efficiencies of Yb3+‐Er3+ activated up‐conversion phosphors are determined by the efficiency of the excitation process and by that of the final emission process in the Er3+ ion. The former process is dependent on the infrared excitation density. We measured the efficiency of the emission process by excitation to selected Er3+ levels for various host lattices and as a function of Yb3+ and Er3+ concentrations. For one of the best up‐conversion phosphors known at present, , the efficiency of the green emission, is about 6%.

Concentration dependence of the Ce3+ and Tb3+ luminescence of Ce1-xTbxMgAl11O19

Abstract The quenching of the Ce 3+ emission and the increase of the Tb 3+ emission with increasing x of Ce 1- x Tb x MgAl 11 O 19 for x ⪅ 0.35 is ascribed to energy transfer from Ce 3+ to Tb 3+ , which is restricted to nearest rare earth neighbours. This transfer is almost complete at x ≅ 0.35. The decrease of the Tb 3+ emission at higher Tb 3+ concentrations is not due to Tb 3+ concentrational quenching, but due to the limited solubility of Tb 3+ in the CeMgAl 11 O 19 phase.

Divalent europium luminescence in perovskite-like alkaline-earth alkaline fluorides

Abstract The Eu 2+ luminescence of the compounds ABF 3 :Eu 2+ (A = Na, K, Rb, Cs: B = Mg, Ca, Sr) depends strongly on the choice of A and B and on the temperature. The wavelength of maximum emission varies from 360 nm to 610 nm. The compounds with B = Mg show 5d−4f band emission and 4f−4f line emission, both located in the ultraviolet. The other compounds show only 5d−4f band emission in the blue, green or red.

Line emission of SrBe2Si2O7:Eu2+ and BaBe2Si2O7:Eu2+

Abstract The compounds SrBe 2 Si 2 O 7 and BaBe 2 Si 2 O 7 both have the barylite structure. With 254 nm excitation, the Eu 2+ -activated compounds give UV emission peaking at 360 nm (Sr) and at 375 nm (Ba). Maximum quantum efficiencies of 40% (Sr) and 65% (Ba) were measured. The emission consists of a 5d-4f band emission as well as 4f-4f line emission, in contrast to many other Eu 2+ -activated oxides which generally show only 5d-4f band emission. At 77°K, both compounds show only the 4f-4f line emission peaking at 360 nm. At higher temperatures, 5d-4f band emission shows up at the cost of the line emission. A thermal equilibrium is assumed between the lowest excited 5d and 4f levels. The energy difference between these levels, calculated from the variation in the line-band intensity ratio with temperature, was computed to be 0.15 eV (Sr) and 0.09 eV (Ba). The occurrence of the line emission in the barylites is correlated with the weakness of the crystal field at the Eu 2+ ions and with the high quenching temperature of the 5d-4f band emission.

Influence of host lattice on the infrared-excited visible luminescence in Yb3+, Er3+-doped fluorides

Abstract The infrared-excited visible luminescence of a large number of Yb 3+ , Er 3+ -doped oxides is reported. It has been found that a variation of the host lattice may have a strong effect on the intensity and the colour of the emission. This paper gives a summary of the experimental results and a qualitative discussion of some general trends observed on host lattice variation.

Line emission of SrAl12O19: Eu2+

Abstract The luminescence of SrAl12O19: Eu2+ consists of a 5d—4f broad-band emission and of 4f—4f lines, their relative intensities being strongly dependent on temperature. At 77°K mainly line emission is observed.