A. Bril

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.

Luminescence phenomena in compounds with fergusonite structure

Abstract In this paper the luminescence of compounds LnTaO4 (Ln = La, Gd, Y and Lu) is reported. A number of rare-earth ions have been substituted for Ln and further Nb for Ta. The fergusonites YTaO4 and LuTaO4 show luminescence in the ultra-violet (maximum at 335 and 325 nm, respectively). The isomorphous GdTaO4 shows no emission. This is ascribed to energy transfer from TaO4 to Gd, followed by concentration quenching. LaTaO4 shows a blue emission at liquid nitrogen or lower temperatures only. The NbO4 group in the fergusonite tantalates is an efficient luminiscent centre. Energy transfer from TaO4 to NbO4 has been observed. Apart from the u.v. (blue) emission the TaO4 (NbO4) group also gives an emission situated at longer wavelengths with a lower quenching temperature. This emission is tentatively ascribed to a triplet-singlet transition. The Bi3+ ion gives a bright blue emission in the fergusonite lattices. The efficiency of the Tb3+ and Eu3+ emission in these compounds is also high. This is related to the position of the broad absorption bands of these centres. Strong evidence is presented that energy transfer from TaO4 to Tb3+ (Eu3+) occurs via the charge-transfer state. For the case TaO4 → Tb the critical distance is estimated to be about 10 A. Rare-earth ions without strong absorption in the u.v. region (Sm3+, Dy3+, Er3+) do not quench the host lattice emission considerably. Phosphors based on LaTaO4 are not very efficient.

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%.

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 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.

On the position of the 5D0 level of Eu3+ in AMgF3 (A = K, Rb, Cs)

The position of the 5D0 level of Eu3+ in the lattices AMgF3 (A = K, Rb, Cs) has been derived from the 5D0-7F0 luminescence transition. For A = Rb or Cs the 5D0 level is situated at very high energies, which is correlated with the chemical bonding properties of Eu3+ in these lattices.

Green luminescence of CsCaF3:Eu2+

Abstract Efficient green luminescence is reported for the Eu 2+ -activated fluoride CsCaF 3 .

Energy transfer from Ce3+ to Tb3+ in scandium borate

Abstract In ScBO 3 energy transfer has been observed from the lowest and from the one-but-lowest excited level of the Ce 3+ ion to the Tb 3+ ion.