Nobuhiko Yamashita

Luminescence Centers of Ca(S : Se) Phosphors Activated with Impurity Ions Having s2 Configuration. I. Ca(S : Se) : Sb3+ Phosphors

The emission, excitation and reflection spectra at 300, 80 and 15 K were obtained. The blue emission at 442 mµ was observed for CaS:Sb 3+ as well as the well-known yellow-green emission at 540 mµ. In the excitation or reflection spectra, A , B and C bands were found for all phosphors of Ca(S:Se):Sb 3+ investigated. These positions are 392, 345 and 321 mµ for CaS:Sb 3+ , and 428, 376 and 345 mµ for CaSe:Sb 3+ at 80 K. From these peak positions, parameters, F 0 , G , ζ and R th , were calculated with the aid of the theories known in alkali halides. The values of ζ decrease from 0.34 to 0.32 eV as the fraction of CaSe is increased. R th is about 6.8 for all the phosphors of Ca(S:Sb):Sb 3+ investigated.

Investigation of TLD Phosphors by Optical Excitation ?Luminescence of Eu2+ Centers in MgSO4, CaSO4, SrSO4, BaSO4?

The photoluminescence (PL) and excitation spectra of various thermoluminescence dosimetry (TLD) phosphors were measured at temperatures of 6, 17, 80 and 300 K. Their PL spectra at 300 K consist of a single band in the vicinity of 380 nm. The emission bands and their excitation bands are ascribed to the electronic 4f6 5d ↔4f7 transitions in the Eu2+ ions. In the PL spectra of MgSO4:Eu2+, SrSO4:Eu2+ and BaSO4:Eu2+, the emission lines due to the electronic 4f7 →4f7 transition in the Eu2+ ion were also observed near 360 nm, in addition to the broad band. No line emission due to the Eu3+ center was observed in any of the phosphors prepared in the present work. In CaSO4:Eu2+ cooled to low temperatures, phonon structures are observed on the emission band and the low-energy excitation band. The TL emission spectra of BaSO4:Eu2+ at various temperatures were also measured.

A new method for recognizing organic vapor by spectroscopic image on cataluminescence-based gas sensor

Abstract ‘Cataluminescence’ is a kind of chemiluminescence emitted during catalytic oxidation of combustible gas. This paper describes a new method using a system which can measure spectroscopic images on a cataluminescence-based sensor to discriminate and determine concentrations of organic vapors in air. Using this equipment, we can measure continuously the image of ‘cataluminescence’ intensity, which reflects the type and concentration of organic vapor, as a function of wavelength and catalyst temperature. Not only the difference between alcohol and ketone, but also the kind of alcohol, e.g. ethanol and butanol, can be distinguished and determined quantitatively by means of this system.

Analytical detection system of mixed odor vapors using chemiluminescence-based gas sensor

Abstract A chemiluminescence(CL)-based gas sensor made of γ-Al2O3 emits CL during catalytic oxidation of a combustible odor vapor. The CL intensity is proportional to the concentration of ethanol or acetone vapor in air. The algebraic sum rule is applicable to the CL intensities by the mixed gas of these two kinds of vapors, when the sensor is heated above 450°C. The CL intensities are measured in periodic temperature cycles between 650 and 450°C. The concentrations of vapor components can be detected analytically by measuring total CL intensities during the high and low temperatures for air containing mixed vapors of various concentrations of ethanol below 400 ppm and acetone below 200 ppm.

High sensitive hydrocarbon gas sensor utilizing cataluminescence of γ-Al2O3 activated with Dy3+

A new method using cataluminescence (CTL)-based gas-sensor detecting hydrocarbon in air is proposed. CTL is a kind of chemiluminescence (CL), which is emitted during catalytic oxidation of organic vapors, e.g., ethanol and acetone. By depositing Dy on the γ-Al2O3 catalyst, we measured the extra CTL spectrum due to Dy3+ during the catalytic oxidation of hydrocarbon gas, while no such CTL was emitted from the γ-Al2O3 catalyst without Dy. By investigating the luminescence mechanism of Dy, the existence of active species produced in a course of catalytic oxidation to excite Dy directly was clarified. The CTL-based gas-sensor using γ-Al2O3 activated with Dy3+ has high sensitivity and linear characteristic. The detection limit of iso-butane in air is 0.2 ppm.

Photoluminescence Properties of Cu + Centers in MgS, CaS, SrS and BrS

The detailed emission and excitation spectra and the temperature dependence of the excitation efficiency are obtained for MgS:Cu+, CaS:Cu+, SrS:Cu+ and BaS:Cu+ at various temperatures between 16 and 293 K. In the excitation spectra of all the powder phosphors, two bands assigned to the intraionic transitions in the Cu+ ion are observed. The luminescence mechanism is explained by the isolated Cu+ ion model. The temperature dependence of the excitation efficiency suggests that the Cu+ ion in CaS, SrS and BaS occupies an off-center position of the sulfur octahedron.

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 Spectra of Eu2+ Centers in Ca(S, Se):Eu and Sr(S, Se):Eu

Photoluminescence and excitation spectra are observed for Ca(S, Se):Eu2+ and Sr(S, Se):Eu2+ powder phosphors at various temperatures between 4.2 and 300 K. The emission band of Ca(S1-x Sex ):Eu2+ at 300 K shifts almost linearly with an increase in x, from 652 nm (x=0) to 597 nm (x=1). In Sr(S1-x Sex ):Eu2+, the emission band shifts also linearly from 620 nm (x=0) to 571 nm (x=1). At low temperatures, vibronic structures on emission bands are observed for CaS:Eu2+, CaSe:Eu2+, SrS:Eu2+ and SrSe:Eu2+. The excitation processes are attributed to two transitions; the intraionic 4f7→4f65d transition within Eu2+ and the fundamental absorption by host crystal, followed by the transfer of the excitation energy to an unexcited Eu2+ ion.

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.

Cataluminescence-Based Gas Sensors

Cataluminescence (CTL) is chemiluminescence emitted in a course of catalytic oxidation. Since 1990, the present authors and coworkers have observed CTL during the catalytic oxidation of various organic vapors in air. This phenomenon has been applied to the CTL-based sensors for detecting combustible vapors. THE CTL response is fast, reproductible and proportional to the concentration of the combustible vapors of ppm orders in air. Based on two types of models of the CTL, the relationship between the CTL intensity and the rate of catalytic oxidation have been investigated analytically. In this article, the effects of catalyst temperature, gas flow-rate and gas concentration on the CTL intensity are demonstrated. Finally, various types of sensing system using the CTL-based sensor are proposed. The results of discrimination and determination of more than ten types of vapors of various concentrations are shown.