Sumitada Asano

Luminescence of Pb2+ Centers in SrS and SrSe Phosphors

The emission and excitation spectra of the SrS: Pb 2+ and SrSe: Pb 2+ phosphors were measured at low temperatures. The 3 A 1u → 1 A 1g emission band at 374 or 392 nm is observed at 80 K in addition to the 3 T 1u → 1 A 1g emission band at 368 or 383 nm for SrS: Pb 2+ or SrSe: Pb 2+ , respectively. On these emission bands, phonon structures appear at 6 K. The zero-phonon line on the 3 A 1u → 1 A 1g emission band grows under the external magnetic field. The sharp excitation band observed at 351 nm for SrS: Pb 2+ or at 368 nm for SrSe: Pb 2+ at 80 K is assigned to the A band in the isolated Pb 2+ center. The excitation mechanism in the high energy region is explained as the transfer of the excitation energy from the host crystal to an unexcited Pb 2+ ion. It is confirmed that the rigid rotator model which explains admixture between the 3 T 1u and 3 A 1u states is also available for the complex Pb 2+ (S 2- ) 6 or Pb 2+ (Se 2- ) 6 in these phosphors.

Photoluminescence of Sm3+ Ions in MgS, CaS, SrS and BaS Phosphors

Details of emission and excitation spectra of powder phosphors were obtained at various temperatures between 6 K and room temperature. The emission spectra consist of six groups of emission lines located at about 565, 605, 650, 710, 790 and 900 nm at 300 K. The position of each emission line shifts slightly towards shorter wavelengths in the order, MgS:Sm 3+ , CaS:Sm 3+ , SrS:Sm 3+ and BaS:Sm 3+ . The first five groups are assigned to the transitions from the 4 G 5/2 state to the 6 H J ( J =5/2, 7/2, 9/2, 11/2, 13/2) states and the last group to the 6 F J ( J =1/2, 3/2, 5/2) states in a Sm 3+ ion. The excitation processes are explained as being due to three transitions; (i) the transitions within the 4 f 5 configuration in a Sm 3+ ion, (ii) the electronic 4 f 5 →4 f 4 ·5 d transition in a Sm 3+ ion and (iii) the fundamental absorption in host crystal, followed by the transfer of the excitation energy to an unexcited Sm 3+ ion.

Luminescence Centers of Ca(S:Se) : Bi3+ and CaO : Bi3+ Phosphors

The emission, excitation and reflection spectra at 300, 80 and 13 K were obtained. For CaS:Bi 3+ , the green (515 mµ) and orange (588 mµ) emission bands are observed as well as the well-known blue (450 mµ) emission band at 300 K. CaSe:Bi 3+ shows blue-green (500 mµ) and red (645 mµ) emission bands at 80 K. CaO:Bi 3+ shows only one emission band in UV region (393 mµ at 300 K). Phonon structures are observed in some of the emission and excitation bands of CaS:Bi 3+ and CaO:Bi 3+ at low temperatures. the peaks of A , B and C excitation bands are found at 412, 347 and 312 mµ for CaS:Bi 3+ , and at 452, 385 and 344 mµ for CaSe:Bi 3+ at 80 K. The values of ζ calculated from these energies are 0.44 eV for CaS:Bi 3+ and 0.38 eV for CaSe:Bi 3+ .

Luminescence Centers of Ca(S: Se): Sn2+ Phosphors

Emission, excitation and reflection spectra at various temperatures are studied. Under the C -band excitation, a simple emission band independent of the activator concentrations is observed for all the Ca(S: Se): Sn 2+ phosphors. As the fraction of CaSe is increased, the band-peak (545 mµ for CaS: Sn 2+ at 77 K) shifts constantly towards shorter wavelengths and finally reaches 518 mµ in CaSe: Sn 2+ at 77K. In the excitation spectra, the curves characteristic of the Tl + -type ion center in the O h crystal field can be obtained for all the Ca(S: Se): Sn 2+ phosphors. The peaks of the C , B and A excitation bands are found at 311, 332 and 364 mµ for CaS: Sn 2+ , and at 327, 344 and 373 mµ for CaSe: Sn 2+ at 77 K. For all the Ca(S: Se): Sn 2+ phosphors, two additional excitation bands (409 and 448 mµ for CaSe: Sn at 77 K) are observed in the longer wavelength region of the A band at low temperatures.

Luminescence of Sb3+ Centers in MgS Phosphors

Emission and excitation spectra of MgS: Sb 3+ phosphors are measured at various temperatures. In addition to the A , B and C excitation bands peculiar to Tl + -type ions, three bands corresponding to charge transfer transitions are observed. On each excitation band, distinct Jahn-Teller splitting is observed and the phonon structure appears on the B band. The energy parameters for Sb 3+ centers in MgS are determined from the excitation spectra.

Investigation of the Luminescence in the SrS: Bi3+ Phosphor by Time-Resolved Emission Spectroscopy

The details of the luminescence spectra and the decay characteristics of the luminescence have been examined over a wide range of temperature. At low temperatures, the luminescence decay curve after the A -band excitation has two components, fast and slow. The difference between the decay times, about 10 ns and 4.1 ms at 4.2 K, enables one to decompose the emission spectrum into the 3 T 1u → 1 A 1g and 3 A 1u → 1 A 1g bands by time-resolved emission spectroscopy. The zero-phonon line at 445.3 nm of the former band and the zero-phonon line ( A 0 ) at 460.7 nm and the one-phonon line at 465.0 nm of the latter band are observed at 6 K. The A 0 line grows under an external magnetic field. The optical excitation mechanism has been also examined by observing the excitation spectra at various temperatures.

Photoconduction du Sulfo-Séléniure de Cadmium en Couche Evaporée

Some films of the solid solution Cd(S:Se) are prepared by vacuum evaporation. When the temperature of the glass plate or quartz plate used as a support is raised regularly from 300° to 600°C with increasing CdSe proportion, films with nearly constant hexagonality of about 80% are obtained. The c-axis of hexagonal cristallites is oriented perpendicularly to the plane of film. The spectroscopic studies and the measurements on thermally excited current and temperature dependence of photo-current yield show that some deep hole traps and shallow ones are formed in addition to deep electron traps and shallow ones. The ionization energies of these electron and hole traps as well as the band gap are regularly reduced with CdSe proportion. The experimental results are compared with those obtained previously for Cd(S:Se) Single crystals and some remarkable differences are found.

PHOTOLUMINESCENCE PROPERTIES OF ZNF2:MN2+, (ZN, MN)F2 AND MNF2

Emission and excitation spectra and luminescence lifetimes of ZnF 2 :Mn 2+ , (Zn, Mn)F 2 and MnF 2 , all specimens in powder form, are observed at various temperatures between 2 and 300 K. The emission band of ZnF 2 :Mn 2+ is located at 583 nm at 300 K and 593 nm at temperatures below 80 K. The feature of the emission spectrum of (Zn 1- x Mn x )F 2 at 16 K is unchanged up to x =0.8. In MnF 2 , the luminescence originates from Mn 2+ ions perturbed by small concentrations of Zn 2+ , Ca 2+ and other impurities. The intrinsic luminescence of pure MnF 2 is unobservable even at 2 K. The excitation spectra of ZnF 2 :Mn 2+ , (Zn, Mn)F 2 and MnF 2 are extremely similar to each other because the electronic levels of the Mn 2+ ion is determined predominantly in the cluster [MnF 6 ] 4- with a slightly distorted octahedral coordination.

Photoluminescence and excitation spectra of the SrO:Bi3+ phosphor

Abstract The details of the photoluminescence and excitation spectra are obtained at various temperatures between 6 and 300 K. At low temperatures, the emission band originating from the 3 A 1u (sp) → 1 A 1g (s 2 ) transition in a Bi 3+ ion shows vibrational structure. In the excitation spectra, the A- and C-bands are observed at 365 and about 250 nm, respectively.