The boron effect on low temperature luminescence of SrAl2O4:Eu, Dy

Abstract

Temperature dependence of the afterglow of persistent luminescence material SrAl 2 O 4 :Eu,Dy is a major problem for outdoor low temperature applications. Therefore this publication deals with tailoring the material for better outdoor use by exploring the second mechanism, that is involved in the afterglowcharge tunnelling from the trapping center to the luminescence center. Structure, morphology, emission and thermally stimulated luminescence properties have been measured for SrAl 2 O 4 :Eu,Dy samples with different added boron percentage. The results indicate a change in morphology of the samples with increasing boron concentration, as well as a change in afterglow times. The low temperature luminescence intensity and afterglow time dependence of boron addition turns out to be different from the room temperature luminescence intensity and afterglow time dependence from boron concentration. Boron addition in necessary amount plays a key role to creating trapping centers in the material that are located spatially close to the luminescence center thus making the material afterglow possible even in low temperatures.

Low temperature afterglow from SrAl2O4: Eu, Dy, B containing glass

“…1 at% Eu, 2 at% Dy SrAl 2 O 4 samples were prepared with 5 and 7 at% of boron (labelled as 5% B and 7% B, respectively). However, not all the added boron successfully incorporates in the lattice of the microparticles as shown in the XPS analysis in [8] -the resulting samples contain 3.70 and 6.05% of B, respectively. The SrAl 2 O 4 : Eu, Dy (with 0.05 and 0.07 B addition) particles were then added in the glass with the composition 90NaPO 3 -10NaF (in mol%) using the direct doping method as in [10] .…”

“…SrAl 2 O 4 :Eu,Dy is one of the most efficient persistent luminophores known up-to-date [ 2 , 3 ]. The afterglow can be observed for up to 20 hours after removing the excitation [1][2][3] . Due to its strong and extensive afterglow, SrAl 2 O 4 : Eu, Dy luminophore is widely used in many applications -emergency signs, luminous paints, luminescent coatings, in vivo imaging [2][3][4][5][6] .…”

“…However, luminophores from Eu doped aluminate group lose 90% of their afterglow efficiency in temperatures below zero Celsius, which is a major problem for material outdoor use [7] . Recently it has been observed, that the addition of boron between 5 and 7 at% in SrAl 2 O 4 :Eu,Dy during the synthesis led to particles with afterglow even in temperatures as low as 10K, however the reasoning for this is unclear [8] . As for the other drawback, the PL (persistent luminescent) luminophores are usually obtained during synthesis in the form of non-transparent powders thus limiting the excitation and emission to the surface of the material and therefore wasting the material in the volume.…”

“…In the present study, Eu, Dy, and B doped SrAl 2 O 4 samples were synthesized using the sol-gel method described in [8] . 1 at% Eu, 2 at% Dy SrAl 2 O 4 samples were prepared with 5 and 7 at% of boron (labelled as 5% B and 7% B, respectively).…”

“…For thermally stimulated luminescence (TSL) measurements, the samples were cooled with Sumitomo HC-4 closed-cycle helium cryostat, temperature range 9 -325 K. Lake Shore 331 Temperature controller was used for temperature control as well as for sample heating (6 K/min) during TSL measurements up to 320 K. The excitation source for TSL measurements was X-ray tube with W target (30kV, 10 mA), the samples were irradiated for 20 minutes and the measurement was initiated right after the termination of excitation. SrAl 2 O 4 : Eu, Dy particles with 5% and 7% B addition were chosen in this study due to their excellent afterglow at 10K as reported in [8] . The reader is referred to this paper for a complete characterization of the particles.…”