Luminescence of CsI and CsI:Na Films under LED and X-ray Excitation

Abstract

In this study, we investigated the luminous properties of undoped cesium iodide (CsI) and Na-doped CsI (CsI:Na) films deposited by thermal vacuum evaporation and treated with different substrate temperatures, post-annealing temperatures, and deposition rates. The quality of the deposited films was evaluated by their XRD pattern, SEM cross-section/surface morphologies and UV/X-ray luminescence, the spectra of which were used to derive the luminescence mechanism of the deposited films. The 310 nm luminescence demonstrates that the exciting light arises from the electron–hole recombination through the self-trapped exciton (STE) process, which is characteristic of the host polycrystalline CsI. The broad-band luminescence from ~400 to 450 nm demonstrates the other electron–hole recombination between the new energy states created by doping Na in the forbidden gap of CsI. When we deposited higher quality films at a substrate temperature of 200 °C, the undoped CsI films showed preferred crystal orientation at (200), and the CsI:Na films co-evaporated by 1 wt.% NaI at (310) and had the highest UV/X-ray luminescence.

Research progress on preparation methods and deliquescence resistance of micro-columnar CsI scintillation films

“…However, the films protected by the parylene-N layer did not form massive grains and still had a clear columnar structure. In 2019, Hsu et al compared the deliquescence resistance of SiO2 film, Al film and Parylene-N film on CsI films 36 . Figure 7 shows the surface morphology of three protective films after being placed in humid air for a long time.…”

Study of waveform characteristics of scintillator detector excited by ultraviolet light-emitting diodes

“…In most cases, the incident photon energy is lower than the ionization energy. This energy thus can only excite electrons to the exciton levels in the forbidden band, rather than ionizing the electrons directly to the conduction band [16,17]. However, the electrons can be ionized directly to the conduction band when the energy difference between adjacent energy levels is smaller than the incident photon energy [18].…”

“…It is should be noted that the luminescence centers of both photoluminescence and radioluminescence for most inorganic scintillators are located in their band gaps [16,17]. Additionally, the luminescence process is actually the energy level transition of electron located in the outer layer of the activating ions (the luminescence center).…”

“…Additionally, the luminescence process is actually the energy level transition of electron located in the outer layer of the activating ions (the luminescence center). To a certain extent, for commonly used inorganic scintillators (such as GAGG(Ce) [20], BGO [21], and alkali metal halides [17]), the photoluminescence and radioluminescence mechanisms are similar.…”

“…Ultraviolet (UV) light can also be used to stimulate scintillators to produce the required fluorescence. UV light has many applications in scintillator testing, including measurement of the scintillator emission spectrum [8] and the components of the scintillator materials [9], along with examination of their luminous performance [9][10][11] and the effects of lattice defects, impurities and their concentrations [12][13][14]. However, UV light is rarely used in measurements of energy resolution and luminescence decay time.…”