Temperature Dependence Of Luminescence Spectra Research Articles

Bright and fast scintillations of an inorganic halide perovskite CsPbBr3 crystal at cryogenic temperatures

Highly efficient scintillation crystals with short decay times are indispensable for improving the performance of numerous detection and imaging instruments that use- X-rays, gamma-quanta, ionising particles or neutrons. Halide perovskites emerged recently as very promising materials for detection of ionising radiation that motivated further exploration of the materials. In this work, we report on excellent scintillation properties of CsPbBr3 crystals when cooled to cryogenic temperatures. The temperature dependence of luminescence spectra, decay kinetics and light yield under excitation with X-rays and α-particles was investigated. It is shown that the observed changes of spectral and kinetic characteristics of the crystal with temperature can be consistently explained by radiative decay of free excitons, bound and trapped excitons as well as electron-hole pairs originating from their disintegration. It has been found that the crystal exhibits a fast decay time constant of 1 ns at 7 K. The scintillation light yield of CsPbBr3 at 7 K is assessed to be 50,000 ± 10,000 ph/MeV at excitation with 12 keV X-rays and 109,000 ± 22,000 ph/MeV at excitation with α-particles of 241Am. This finding places CsPbBr3 in an excellent position for the development of a new generation of cryogenic, efficient scintillation detectors with nanosecond response time, marking a step-change in opportunities for scintillator-based applications.

ZnSe nanocrystals obtained in pores of SiO2 matrix with temperature stable green luminescence

ZnSe nanocrystals have been obtained in the pores of SiO2 matrices by two different methods – chemical vapour deposition (CVD) method and method of impregnation of SiO2 matrices with ZnCl2 solution and subsequent annealing in H2Se atmosphere. Luminescence spectra of ZnSe nanocrystals are characterized by wide green band which intensity remains equally high as at 77K, so at 300K contrary to ZnSe bulk crystal in which intensity of this band drops almost to zero at temperatures above 150K. Analyses of temperature dependences of luminescence spectra and decay curves have shown that the quenching of the green band in bulk and nanocrystals occurs via different mechanisms – while for bulk crystals quenching takes place with participation of the bottom of conduction band (CB), for nanocrystals this mechanism becomes ineffective due to sufficient blueshift of the bottom of CB determined by quantum size effect and quenching is restricted to direct energy transfer to nonradiative defect sites of nanocrystal.

Mechanism of band-edge luminescence in cuprous iodide single crystals

The photoluminescence spectra of CuI crystals using synchrotron radiation as an excitation light source were obtained at 60K. The emission peaks at 405, 415, 420 and 443nm were observed. The possible origins of these peaks were discussed by the temperature dependence of luminescence spectra for CuI material. Meanwhile, the photoluminescence spectra of CuI powder with different excitation intensity were measured and the ultrafast luminescence component of CuI crystals was warranted to be attributed to the recombination of donor acceptor pair. Furthermore, the excitation process was studied by measuring the photoluminescence excitation spectra of CuI crystals and powder.

Temperature dependence of time-resolved luminescence spectra for 1D excitons in single-walled carbon nanotubes in micelles

We have investigated exciton luminescence spectra, decay behaviors, and their temperature dependence in single-walled carbon nanotubes in micelles. The temperature dependence of luminescence spectra can be explained by the one-phonon process associated with the radial breathing mode in the single-walled carbon nanotube. The luminescence decay behavior suggests that the signal is composed of various exponential decays with different decay times. These experimental results are explained by the existence of trapping centers on the nanotube.

Relaxation Process of CT Exciton State in a One-Dimensional MX-Chain Compound NiBr( chxn ) 2 ]Br 2

Luminescence spectroscopy measurements were performed in a one-dimensional halogen-bridged transition-metal compound [NiBr( chxn ) 2 ]Br 2 ( chxn : 1 R ,2 R -cyclohexanediamine) and its mixed-metal compound [Ni 1 m x Pd x Br( chxn ) 2 ]Br 2 with x=0.005, 0.05, 0.33. The broad peaks were observed at 1.3 and 1.4 eV for [NiBr( chxn ) 2 ]Br 2 , which are attributed to a relaxation of LMCT exciton state and a hot luminescence, respectively. No Stokes shift of the luminescence at 1.3 eV was observed, which shows the electron-lattice interaction ( S ) is weak in this system. From the temperature dependence of luminescence spectra, it was clarified that the relaxation process is continuously changed from luminescence to thermal relaxation. The luminescence peak at 1.3 eV is remarkably quenched with increase of x for [Ni 1 m x Pd x Br( chxn ) 2 ]Br 2 , implying that the LMCT exciton is trapped to in-gap states caused by doped Pd 3+ . MX chain luminescence charge-transfer exciton mixed valence

Specific features in the temperature dependence of photoluminescence from CdTe/ZnTe size-quantized islands and ultrathin quantum wells

A study has been carried out of the temperature dependences of luminescence spectra on a large number of CdTe/ZnTe structures differing in average thickness, 〈L z〉=0.25–4 monolayers (ML), and CdTe layer geometry (continuous, island type). The influence of geometric features in the structure of ultrathin layers on linewidth, the extent of lateral localization of excitons, their binding energy, and exciton-phonon coupling is discussed. It is shown that in island structures there is practically no lateral exciton migration. The exciton-phonon coupling constant in a submonolayer structure has been determined, Γph=53 meV, and it is shown that in structures with larger average thicknesses Γph is considerably smaller. Substantial lateral exciton migration was observed to occur in a quantum well with 〈L z〉=4 ML, and interaction with acoustic phonons was found to play a noticeable part in transport processes. It has been established that the depth of the exciton level in a quantum well and structural features of an ultrathin layer significantly affect the temperature dependences of integrated photoluminescence intensity.

Electronic States and Energy Transfer in PbI2Clusters Dispersed in CdI2Crystals

Luminescence associated with small PbI 2 clusters formed in Pb 1- x Cd x I 2 solid solutions has been investigated in the range of x between 0.4 and 0.9. Time-resolved measurements reveal that the luminescence at the absorption edge of crystals consists of the bands with short (sub-ns) and long (µ s ) decay times. The two bands are found to originate from the states related to 3 P 1 and 3 P o of Pb 2+ ions. The energy split between the two states increases with decrease in the size of PbI 2 clusters. The result is explained by the change in an exchange energy of electron and hole with the cluster size. Dependences of luminescence decay times on the luminescence and excitation energies indicate that energy transfer takes place among clusters. Temperature dependences of luminescence spectra and decay times are interpreted by the energy transfer process.

Exchange effects on the luminescence of the quasi two dimensional antiferromagnet (C nH 2n+1NH 3) 2MnCl 4 (n=1,2,3)

Temperature-dependence of luminescence spectra are measured of the Heisenberg-type two dimensional antiferromagnets: (C nH 2n+1 NH 3) 2MnCl 4 with n=1,2, and 3 in the temperature range of 4–300K. The marked changes of the band position, halfwidth, intensity and lifetime are observed near the Neel temperature. The results are discussed in terms of the magnetoelastic effect due to exchange interaction. The intralayer exchange interaction J and the Neel temperature derived from the luminescence measurements are in accordance with the magnetic ordering of nearly isolated layers.

On the nature of emission bands of self-trapped excitons in solid xenon

The paper presents the analysis of experimental data on the temperature dependence of luminescence spectra of solid xenon. The mechanisms of exciton self-trapping down to quasi-molecular states under different conditions are discussed. A new treatment of spectral distribution of intensity through quasi-molecular luminescence bands is proposed; according to the treatment, at T < 55 K the emission is associated with the transition from the lowest vibrational relaxation excited state 3Σ u +, while at T 60 K from the term 1Σ u +. Spectral redistribution of intensities in the 60–150 K range is due to an increase in the rate of vibrational relaxation in the state 1Σ u + with increasing the crystal temperature.