1. Effect of air annealing on TL properties
in irradiated hexagonal boron nitride powders
Maxim G. Minin1, Ilya A. Weinstein1, Alexander S. Vokhmintsev1,
Ahmed Maher Ahmed Henaish1,2, Vadim V. Kartashov1, Ivan V. Chernetsky1
1Ural Federal University, NANOTECH CENTER
Mira street, 19, Ekaterinburg, Russia, ,
2Tanta University, Physics Department, Tanta, Egypt, 31527
INTRODUCTION
Hexagonal boron nitride is considered to be promising multifunctional wide gap material. Numerous researches of optical properties for h-BN were performed in middle UV region where laser generation is observed. On the other hand, use of boron nitride as a radiation sensitive matrix requires improvement of visible luminescence characteristics, originating from intrinsic and extrinsic defect complexes. Varying synthesis methods and following thermal treatment are the key instruments for optimization of emission response to the ionizing radiation. In this connection the goal of the present research was the study of the thermal treatment effect on the thermoluminescence response in UV-irradiated h-BN.
SAMPLES AND EXPERIMENTAL TECHNIQUE
h-BN powder synthesized using carbamide technique (Company «Unichim & EP») have been studied. Samples under study had a typical flake-like morphology and consisted of 98.9 wt.% of boron nitride, 0.17 wt.% of boron anhydride and 0.22 wt.% of carbon. Average particle agglomerates size was 20µm.
TL studies were performed on the laboratory spectrometric installation based on Perkin Elmer LS 55 luminescence spectrometer. h-BN powder was exposed to monochromatic (210 nm) and UV-radiation from the Xe lamp for 5 min. Thermally stimulated emission was registered during heating up to 700 K with constant rate 2 K/s. Annealing of the powder was performed at 773 K for intervals from 0 to 240 min. Changes in TL response were measured.
To measure the TL spectra powder was exposed to 210 nm UV-radiation from the Xe lamp for 15 min. After that the powder was heated within the RT – 700 K range with the rate of 0.5 K/s. TL spectra were registered in every 15 K within the 325 – 525 nm range and scanning rate 800 nm/min. Temperature variation of the sample and luminescence intensity of a spectrum was neglected during the measuring time (≈15 s).
1. Annealing, T = 773 K, ta = 10 min
2. Irradiation,
ex = UV, 210 nm, ti = 5 min
3. TL measurement
em = 330, 380, 425 nm
Technique
h-BN powder under study
National Instruments PXI-6259 & LabVIEW
Experimental spectrometric installation
Perkin Elmer LS 55 with heating module
RESULTS AND DISCUSSION
3D plot for non-annealed h-BN powder
TL glow curves decomposition
Annealing effects
Relative TL lightsum
Irradiation
ta, min
em, nm
330
380
425
210 nm
1.00 30
1.24
1.38
1.16 60
1.44
1.31
1.14
unfiltered UV —
2.31
1.29
3.39
120 —
2.39
3.89
240
0.45
0.57
Kinetic parameters of TL
em, nm
Peak
Tmax, K
EA, eV
s, s-1 b
330 I
336
1.04
9.85∙1014
1.30
380
338
0.95
2.71∙1013
1.49
III
588
6.65∙106
1.00
425
337
0.98
6.93∙1013
1.75 II
493
3.97∙109
598
0.85
1.02∙106
The formalism of general order kinetics
here T0 is the initial temperature, K; r is heating rate, K∙s-1; k is the Boltzmann constant, JK-1; n0 is the initial concentration of charge carriers captured on traps, m-3; b is the kinetics order; s is the effective frequency factor s-1; and EA is the activation energy, eV.
CONCLUSIONS
PUBLICATONS
Spectral and kinetic regularities of thermally stimulated luminescence in the h-BN powder following the UV light irradiation (210 nm and unfiltered) were studied.
Three emission bands 330, 380 and 425 nm were observed.
TL glow curves were decomposed using the formalism of general order kinetics. Parameters of the bands are compared with the results obtained with different irradiation conditions on the same samples.
Relative changes of TL lightsum were evaluated for samples with variable annealing time (from 0 to 240 min). It is shown that lightsum arises following the initial annealing. It value reaches maximum at 30 min and 120 min in 380 nm band for irradiation with monochromatic and unfiltered UV light respectively.
Further investigation is required for determination optimal regimes of annealing to increase the TL response of h-BN usage as dosimetric material.
Weinstein I.A., Vokhmintsev A.S., Minin M.G., Kartashov V.V., Chernetsky I.V., Spectral and kinetic features of thermoluminescence in hexagonal boron nitride powder after UV-irradiation. Radiation Measurements.
Kubota Y., Watanabe K., Tsuda O., Taniguchi T., Deep ultraviolet light-emitting hexagonal boron nitride synthesized at atmospheric pressure. Science 317, 932–934.
Museur L., Feldbach E., Kanaev A., Defect-related photoluminescence of hexagonal boron nitride. Phys. Rev. B 78, –