Property of Highly Oriented SrAl[sub 2]O[sub 4]:Eu Film on Quartz Glass Substrates and Its Potential Application in Stress Sensor

Abstract

In this paper, a high crystalline SrAl2normalO4:Eu film has been deposited on the quartz glass substrate using the radio-frequency magnetron sputtering method. The crystallinity and surface morphology of the SrAl2normalO4:Eu film were characterized by IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy (AFM). The XRD result indicated that the obtained film was (0 3 1) fiber textured, and the AFM result showed that the film surface was smooth and compact. The important point was that the prepared film displayed strong adhesion and high sensitivity to various mechanical stresses. A green triboluminescence circle and a bright green impact mechanoluminescence can be observed when the mechanical stimuli were applied on the film.

Development of mechanoluminescence technique for impact studies

“…There is a possibility that the macroscopic or bulk piezoelectric field may cause detrapping of the charge carriers and subsequent capture of electrons with the excited state of activator ions or recombination of holes with reduced state of the activator ions may cause the light emission [10,7,[11][12][13]. Generally, the piezoelectric constant d of the crystals is of the order of 10 Â 10 À 12 C N À 1 , and the threshold pressure P th for the EML emission is nearly 10 6 N m À 2 .…”

“…The EML measurement induced by impact stress has been made only for the thin films of ZnS and SrAl 2 O 4 :Eu, in which EML has been excited by dropping a small ball from a low height [13,15]. If E c is the characteristic piezoelectric field, that is, the field needed for reducing the total number of filled electron traps n t0 in the high piezoelectric region near the activators to n t0 /e (where e is the base of natural logarithm), caused by the detrapping due to localized piezoelectric field, then the number n t of the filled electron traps at any time t can be expressed by the following equation…”

“…Fu et al [13] have deposited SrAl 2 O 4 :Eu films onto the quartz glass substrate of size 20 mm  20 mm  1 mm by a combination of the RF magnetron sputtering technique and post-annealing treatment following the method reported previously [45]. In the RF magnetron sputtering technique the source target with a diameter of 4 in.…”

“…For impulsive excitation of EML in SrAl 2 O 4 :Eu film coated on a quartz glass substrate, Fu et al [13] dropped a ZrO 2 ball of mass about 0.088 g and diameter 0.30 cm from a height of 2.5 cm. For impulsive excitation of EML in ZnS film coated on a quartz plate, Xu et al dropped a small ball of mass 5.57 g and radius 0.70 cm from a height of 17 cm.…”

“…Although the phenomenon of ML is known for a long time, up to the end of twentieth century, no remarkable practical application of mechanoluminescent materials could be made because of their low ML intensity and lack of reproducibility. In the last decade, a variety of materials have been obtained that emit an intensive and repeatable EML during their elastic deformation without any destruction [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The EML of SrAl 2 O 4 :Eu, SrMgAl 6 O 11 :Eu, Ca 2 Al 2 SiO 7 :Ce, ZrO 2 :Ti, etc.…”