Studies Mecanoluminescence by impulsive deformation of strontium aluminates nanophosphor (nilam Chandrakar)

CERTIFICATE This is to certify that Miss Nilam Chandrakar of solid lab has completed the dissertation entitled “ Studies Mecanoluminescence by impulsive deformation of strontium aluminates nanophosphor ” under my supervision for the fulfillment of the Master degree of science in physics.

Dr. Nameeta Brahme Reader S.o.S. in physics & Astrophysics Pt. Ravishankar Shukla University Raipur (C.G.)

CONTENNTS S.NO.

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PREFACE ACKNOWLEDGEMENT CHAPTER – 01 - LUMINESCENCE 1.1 Introduction 1.2 Types of luminescence 1.3 Mechanoluminescence 1.3.1 Introduction 1.3.2 Mechnoluminescence materials 1.3.3 Parameters of ML measurement 1.3.4 Application of ML 1.3.5 Outline of the present work

CHAPETER – 02 - GROWTH OF PHOSPHOR 2.1 Introduction 2.2 Different methods of growing phosphor 2.3 Phosphor growth from combustion methods (SrAl2O4:Eu2+)

CHAPTER – 03 – MECHANOLUMINESCENCE DURING IMPULSIVE EXCITATION IN IRRADIATED Eu2+ DOPED SrAl2O4 PHOSPHOR 3.1 Introduction 3.2 Experimental 3.3 Results

CHAPTER – 04 – DISCUSSION AND CONCLUSION 4.1 Discussion 4.2 Mechanism of mechnoluminescence in UV- irradiated SrAlO : Eu phosphor 4.3 Conclusion

CHAPTER LUMINENESCENCE

1.1 INTRODUCTION Matters can absorb energy from several sources, when certain substance absorb energy then a part of the absorbed energy may be re-emitted as electromagnetic radiation in excess of thermal radiation. Such cold emission of light is known as luminescence. The mechanism of luminescence involves at least two steps first, the excitation of the electronic system of substance by internal energy and second the subsequent emission of photons. These two steps may or may not be separated by intermediate processes.

Luminescence is simple process whereby radiation in a narrow band is emitted as a result of change in energy states usually of electrons, when the substance is excited by external source of temperature of the sample and hence it is often called cold light. Firefly, oscilloscope, screen, T.V. screen, LED self luminous watch dial are cold light sources.

Luminescence is a generally term for the emission of electromagnetic radiation from the substance during or following the absorption of energy from suitable source such as U.V radiation, X-rays or high energy particle. It is consequence of the radiation recombination of the excited electron. It is distinguished from thermal radiation that it does not follow Kirchhoff’s law and Wein’s law. A time delay in emission of the order of 10-9sec, distinguish it from Raman and Compton effects which are completed in a time of about 10-14 sec or less.

Luminescence process involves at least two steps1.Excitation of electronic system of the substance and, 2.The subsequent emission of photon. These two steps may or may not be separated by intermediate process.

Two of the most important aspects of the luminescence are on the basis of the physical process taking place during fluorescence and phosphorescence, we can say that fluorescence is the emission that take place by the one or more spontaneous transitions and phosphorescence is the emission which occurs with the intervention of the metastable state follow by a return to the excited state due to addition of energy. This energy may be supplied by optical radiation heat.

Another way to different these two phenomenon are fluorescence is the luminescence emitted during excitation or within 10‾8 sec after cessation of excitation. The interval 10-8 is chosen as of the order of the life time of an atomic state for an allowed electric dipole transition in the visible region of the relaxation time of an isolated gaseous ion. If the emission occurs after this interval of removing the excitation luminescence may be called phosphorescence or after glow. The delay period may be of the order of microseconds to hours.

The fluorescence is little dependent on temperature but phosphorescence is strongly temp dependent.

2.TYPES OF LUMINESCENCNCE 1.THERMO-LUMINESCENCE :- It is the emission of light of a sample which is per excited during warring up of the substance to a moderate temperature.

2. MECHANO-LUMINESCENCE :- It is produced during mechanical deformation of solid. It is also known as tribo, piezo and deformation luminescence.

3. PHOTO-LUMINESCENCE :- It is produced by absorption of photos of energy from few to several electron volts. (e.g. ultraviolet radiation).

4. RADIO-LUMINESCENCE

:- It is produced by bombardment of

materials with high energy particles or radiation. (e.g. Gamma rays).

5. CATHODO-LUMINESCENCE :- It is a specific case of radio luminescence produced by cathode rays or a luminescence in which the excitation is achieved by bombardment with high energy electrons or cathode rays.

6. ELECTRO-LUMINENESCENCE :- It is produced by application of D.C. or A.C. electric field

7. CHEMI-LUMINESCENCE :- It occurs in certain exothermal chemical reaction. Where energy is released in photon from rather than heat .

8.BIO-LUMINESCENCE :- It is produced by energy from bioluminescence.

9. ROENTGENO-LUMINESCENCE :- It is a specific case of radio luminescence produced by X-rays.

10. SONO-LUMINESCENCE :- It is produced by ultrasonic wave. 11. CRYSTALO-LUMINESCENCE :- It is produced during growth of crystals from solutions.

12.CANDO-LUMINESCENCE :- It is a non-black body emission observed at very high temperature.

13.MANGNETO-LUMINESCENCE :- It is the change in the intensity of photo luminescence due to magnetic field.

1.3 MECHANO-LUMINESCENCE 1.3.1 INTRODUCTION :- ML is the phenomenon of light emission induced by elastic deformation, plastic deformation and fracture of special class of solid.

“ when certain solids are subjected to stress beyond particular levels. Light emission follow their deformation. This physical process of light emission is known as mechano-luminescenc.

It can be excited either by grinding, cutting, cleaving, shaking, scratching, compressing, or by crushing of solids. ML can also be excited by thermal shocks caused by drastic cooling or heating of material or by the shock wave produced during exposures of samples to powerful laser pulses. ML also appears during the deformation caused by the phase transition or growth of certain crystal as well as during separation of two dissimilar materials in contact.

The ML may divided into three types normally :-

1.RACTO-ML :- In fracto ML the luminescence is produced due to the creation of new surfaces during fracture of solids.

2. PLASTICO-ML :- The plastico ML the luminescence is produced during plastic deformation of solid. Where fracture is not required .

3. ELASTICO-ML :- In elastico ML the luminescence is produced during elastic deformation of solids. Where the plastic deformation of solid and fracture is not required . Mechano luminescence (ML) is a type of luminescence induced during any mechanical action on solids. Grinding, rubbing, or crushing of solids can excite it. ML can also be excited by thermal shocks caused by drastic cooling or heating of during exposure of samples to powerful laser pulses ML also appears during the deformation caused by the phase transition as during separation of two dissimilar materials in contact. The term tribo luminescence was proposed by weidman (1888) originated from Greak word “tribo” means rubbing weidman and schmitt (1895) define the term triboluminescnce as the emission during mechanical treatments like rubbing, cutting, and pressing of solids. where the system is not in equilibrium with radian system is not in equilibrium with radiant system therefore. They might show a higher radiation intensity than the intensity of equi frequency radiation of a blackbody at some temp. the light emission during the mechanical deformation of the solids is not attributed generally to traction. Hence the nomenclature “mechanoluminescence” is preterred in most of recent litretures (chandra and 1980, krauya et al 1981, Motaskil 1983, Mukhopadhyay 1984). The ML dose not appear only in the crystals of insulators and semiconductor. But it appears also in certain metals, glasses and polymers.

1.3.2 MECHANO LUMINESCENCE MATERIAL :Nearly one-half of all inorganic solids and from one-fourth to one third of all organic solids both crystalline and non-crystalline exhibit the phenomenon of ML. It has been observed in and semiconductor as well as in conductors. ML solids can be

divided into the follows six group crystalline, amorphous, polymeric, ceramic composite and tribo machano luminescence. Amorphous materials such as silicates, quartz, borate and other glasses exhibit ML. Krauya et al (1978)u observed ML during fracture of human body tissues. Chandra et al (1982) reported that bones emit light when they fracture.

ML appears during the polymers such as polyethylene, polyvinylidence and polystyrene Nakayama et al (1992) observed ML during stretching of nylon-6 and polytetrafluoroethylene

Generally all non-centrosymmetric crystal i.e. Piezoelectric crystals exhibit ML and those that do not are non piezoelectric certain centro symmetric crystals also exhibit ML. But it has a non piezoelectric origin wolff et al (1952) compiled a list of about 450 ML crystal including inorganic compounds minerals

and aliphatic and aromatic organic compound. 1.3.3 PARAMETERS FOR ML MEASUREMEN’S It is well know that the study of any phenomenon is made with respect to some finite parameters. In the case of ML, on systematic study has been made with respect to some well defined parameters from the survey of literatures the following parameters may be pointed.

1.SPECTROSCOPY OF ML :- The parameter for describing the ML and for its interpretation is the determination of the spectroscopy of ML allows important conclusion concerning the excitation mechanism.

2. EFFICIENCY OF ML :- Efficiency of ML is defined as the radio of emitted energy by applied mechanical energy most of the measurement has been made relatively.

3. TEMPERATURE DEPENDENCE OF ML :- Temperature affects the ML efficiency of solids. Generally all the solids loose their ML behavior beyond a particular temp.

4. CRYSTAL SIZE DEPENDENCE OF ML :-The ML intensity to found is increase with the size of the crystal for a crystal of cubic shape. The total ML intensity is reported to increase linearly with the mass of the crystal (chandra et al1986).

5.EFFECT OF IMPULLIT/DOPANT, IRRADIATION ON THE ML :- ML intensity increase with concentration of do pant and irradiation does and with the temperature of the crystal (R.S. Kher et al1996).

1.3.4 APPLICATION OF FRACTO-LUMINESCENCE (a) STRESS SENSOR :- As the ML intensity of SrAlo:Eu phosphor mixed in a rein increase stress or the applied pressure, the stress or the pressure can be determined using the ML intensity. As such the ML of SrAlO:Eu can be used as stress sensor or pressure sensor or pressure indicator.

(b) REAL-TIME VISUALIZATION OF THE STRESS DISTRIBUTION IN SOLIDS :- The ML of SrAl2O4 : Eu, Dy provides a technique for the direct visualization of stress distribution in solids. For the measurement of stress of stress distribution using ML, Xu et al. mixed SrAl2O4 : Eu phosphor of 1.00g with an optical epoxy resin of 4.00g to form a composite disc of

25 mm in diameter and 15 mm in thickness. Stress is applied on the sample by a normal material test machine or by a vise with a force gauge. The distribution of ML intensity was detected by an intensified CCD (ICCD) camera. The ML increased exponentiallyfrom the centre of the sample. The stress distribution of such a stressed sample was simulated based on elastics. The simulated compressive stress increased exponentially, with increasing r/a (where r is the distance from the center, and a is the radius of sample). This is consistent with that of the measured ML intensity, demonstrating that the ML from stressed SrAl2O4 : Eu gives the direct view of stress distribution, in solids.

(c) REAL-TIME VISUALIZATION OF THE STRESS FIELD NEAR THE TIP OF A CRACK :- For the direct observation of crack tip stress field using the ML of SrAl2O4:Eu,Dy Sohn et al. prepared the comact test(CT) specimen(19mm*20mm*3mm) from a mixture of epoxy resign and 10wt.% of the phosphor. An acute notch tip of radius 50μ m was introduced into the CT specimen using a very sharp blade for providing a crack initiation point. The specimen was placed on an specially designed CT type loading machine and exposed to 365 UV light for 10 min and then aged in a dark room for 5 min for the phosphorescence to relax down to a certain level before loading. The notch tip area was photographed at each loading step using a digital camera with shutter open. The load applied to the specimen was determined using a load cell and thus the instantaneous value of stress intensity factor could be calculated. In this technique, the load was increased by straining the specimen at a speed of 80 m/min until a small crack was created at the edge of the blade-notched tip. The stress intensity, factor of 1.4MPa m½ , gave rise to the initiation of sharp crack. In this case , only a small area near the notch tip was observed. When the sharp crack emanating from the notch tip was detected, the load was removed completely and 365 nm UV light was illuminated again for 10 min to refill the empty traps. After 10 min, the specimen was reloaded up to a certain level of load so that the stress intensity factor increased up to 1.7 Mpa m½ . during this second loading procedure, no further crack growth was observed. Thus, it was possible to investigate the stress field formation in front of a stationary crack tip in

terms of ML for a stress intensity factor of 1.7MPam½, where by the formation of circle-shaped stressed area was evident. Although the boundary of the stressed or luminous area is ambiguous, it is certain that the outermost boundary reached up to about 5.5 mm from the crack tip at θ = 0°. using the radius of the stress area, the threshold stress , which gives rise to ML was determined and it is found to be 13.4MPa.

(d) REAL-TIME VISULIZATION OF THE QUASIDYNAMIC CRACK-PROPAGATION IN A SOLID :- For studing the dynamic visualization of crack propagation and bridging stress using the ML of SrAl2O4 : Eu Kim et al. [9] prepared a disc-shaped CT specimen of dimension 26 mm in dimension and 3 mm thickness from a bulk SrAl2O4 : Eu0.01 ceramic, without mixing epoxy region. The R-curve was determined where the crosshead speed was 1 mm/min and the photography frame speed was 30 frame/sec. The loading process associated with the ML observation was followed by microscopic observation of crack wake region using scanning electron microscopy. The ML images were taken for the crack propagation time of 0.3 sec, whereby the crack propagation nearly 6.5 mm. In this case,the conspicuous ML takes place from the area adjacent to the crack wake region provides a good circumstantial evidence for crack interface bridging and a diminished stress intensity factor at the crack tip. The length of the strong ML region or strong bridging effect region, just behind the crack advances. The R-curve was determined using ML measurements and it was compared with the best fit based on power law bridging stress distribution. The bridging stress distribution in the crack wake was determined from the results of regression fitting used in R-curve. Kim et al. [10] have reported the visualization of fractures, in alumina ceramics using ML paint. Recently, Kim et al. [11] have studied the propagation of a macroscale crack in Mg-partially stabilized zirconia (Mg-PSZ) ceramic using SrAl2O4 mechanoluminescence paint.

(f) NOVEL ML-DRIVEN PHOTOCEL SYSTEM :- Terasaki et al. [19] have successfully demonstrated a novel ML-driven photocell system, in which SrAl2O4 : Eu; microparticles and a commercial silicon solar cell are used as light source and a photoelectric converter, respectively. The ML-driven photocell system seems to be more suitable and useful for a molecularly or nanoscopically ordered photofunctional unit, for example, photoelectric conversion molecules, than the bulk system, because the system certainly has ability to be a ubiquitous electrical source, and furthermore, to be directional electron source to control the configuration between ML nanoparticles and photoelectric photomedical treatment, are much fascinating targets for the ML matrix. To achiv these application in the future, efficient ML materials with many kinds of emission colours are required.

The fracto ML has been found useful in detection of fracture and micro-scratches in the course of deformation. It can also be used for measuring the crack velocity, fracture-inititation time, local stress and temperatures near a moving crack-tip, and phase-transition temperature. Since the measurement of ML intensity can be easily made at time-intervals as short as a few nano-seconds, it may provide a sensitive optical tool for studying the time-resolved fracture dynamics. The fracto ML of a sample may display rapid fluctuations well in excess of the detector and amplifier noise (Lagford etal 1989). The fracto ML may be used for the investigation of the emergence of mobile dislocations on to the metal surfaces may also be studied by using the kinetics of their ML (Molotskii 1989).

ML can also be used for the study of recombination kinetics (Dickinson et al1993). Brady and Rowell (1986) have reported that the fracto ML can suscefully be used for the investigation of the electrodynamics of rock fracture in mines and earthquakes. The fracto ML has also been found useful for the studies of development and interfacial fracture at embedded surfaces of composite materials (Zhenyi and Dickinson 1991), where the observed signal provides time-resolved

information on the sequence of fracture . Such results have been used to model the process of fibre / matric debonding and fibre pullout in a brittle matric composites.

It has been found that generally the non-centrosymmetric crystal exhibit ML and the crystal which do not show ML are centrosymmetric, i.e., nonpiezoelectric. This fact has helped in verifying the point group and space group of crystal. Glass et al(1975) and glass(1977) have repoted that the facto ML of 11-14 compound may be used in wireless fuse-system for army war-heads. Haneman and McAlpine (1991) have reported that the fracto ML of semiconductors can be used to determine their energy band gaps and to understand the surface defects and the electronic structure of the newly created surfaces. Tokhmetov and Vettergren (1990) have reported that the fracto ML can be used to determine the activation energy of fluctuation-induced breaking of chemical bonds in solid. Fracto ML has also been found helpfule in improving the design of fluid energy mills (Bukhari 1977).

1.3.6 OUTLINE OF THE WORK PROPOSED :- The various investigation are made on the ML of solids that are chiefly related to the following parameters; 1) sysntheis of SrAl2O4. 2) ML characteristics . 3) optical cractrisition obserption spectra. 4) dependences on velocity. 5) dependence on mass. 6) ML spectra. 7) To analised the machnism.

During the study of ML, which is extremely complex process, there are just too many unknowns in crushing are often in a fairly indeterminate manner, elastic, plastic and facture processes will come into play. Electrical potentials may be produced via charged facture planes by the movement of charged fracture planes, by the movement of charged dislocation or even via contact potentials differences between the phosphor and crushing device. In addition, the phosphor environment must be considered, notably the nature and pressure of the surrounding gases with so many uncertainties, it is not surprising that understanding the mechanical responsible for exciting the ML has become complex.

The mechanism and the mechanical characteristics of the ML excitation in the colored alkaline earth aluminate understood. Intense ML is observed in the alkali halide crystal, after irradiation with X or ultraviolet. The irradiation creates color center in the phosphor. An electron trapped in the color center is promoted to the conduction band, when the lattice defects are destroyed by elastic or plastic flow and luminescence is observed as the electron recombine with the holes.

The chief interest of the present investigation is to understand the mechanism of impulsive excitation in irradiated Eu2+ doped SrAl2O4 with different concentration of doped material. The present study will respect to the following points. 1) Growth of Eu2+ doped SrAl2O4 phosphor. 2) Measurement of ML produced during impulsive excitation in ultraviolet Eu doped SrAl2O4 phosphor. 3)To study velocity dependence on ML in ultraviolet Eu doped SrAl2O4 phosphor. 4)Load dependence of ML in ultraviolet Eu doped SrAl2O4 phosphor. Dose dependence of ML in ultraviolet Eu doped SrAl2O4 phosphor.

  CHAPTER ­ 02

GROWTH OF PHOSPHOR     

2.1 INTRODUCTION Nanophase material are being vigorously explored as most of the physical properties are size dependent and are markedly affected as the particle sizes tend to nanometer level. Phosphors are one of the materials that show promising behaviour when synthesized in nanophase by employing different techniques. Divalent europium activated alkaline earth aluminates are know to be efficient long persisting phosphor for their high quantum efficiency in the visible region. These are essentially interesting, as they do not involve any radioactive isotope. particularly SrAl2O4:Eu+2 phosphor excited very bright and long lasting phosphorescence (>50) with emission wavelength of 530-540nm. The synthesis of these materials or display application with considerable good initial brightness and long afterglow has been a major goal of many research groups all over the world both in industry and academia for well over a decode. Commonly followed method of preparation of these group of phosphors – (1) sol-gel techniques, (2) microwave heating techniques, (3) hydroxide precipitation, (4) an electric arc method, (5) hydrothermal synthesis, (6) combustion synthesis.

Solid state reaction technique, in which appropriate oxides/ carbonates along with the do pants and fired at temperatures around 1200-1500ºc for a few hoarse . This treatment results in a highly sintered, dense and hard mass of phosphor, which is difficult to crush and grind. Combustion synthesis route gives a fluffy mass reducible to quite fine particle with almost no effort. Condition prevailing during the processing should favor formation of fine particles in sub-micron region oxidizing atmosphere prevails in combustion process. Incorporation of europium in bivalent state invariably requires reducing atmosphere with a view to develop a process for

the instant synthesis of nanophase particles of the phosphor. We employed combustion route. In the present work an attempt to synthesize nanophase SrAl2O4:Eu+2 phosphor by combustion technique with slight modification has been made. The sample have been characterized for nanophase, structural and luminescence proportion.

Compared with sulphide phosphorescent phosphors, aluminates possess several valuable properties: high radiation intensity, long-lasting photoluminescence, colour purity and chemical, thermal and radiation resistance, which result in an unexpectedly large field of application, such as luminous paints on highways, airports, buildings and ceramic products as well as textiles, the dial plates of luminous watches, warning and escape route signs, ets.

2.2 PHOSPHOR GROWTH FROM COMBUSTION METHODS (SrAl2O4: Eu+2) SrAl2O4: Eu+2 phosphor were prepared by combustion synthesis. The starting material included: Al(NO3)3.9H2O(analysis pure; A.P.),Sr(NO3)2 (A.P.), Eu2O3 (99.9%;3N), CO(NH2)2 (A.P.) and HNO3 (1.4 g/ml). Amounts of urea were added as reducer. The powders were weighted according to the stoichiometry Al(NO3)3.9H2O, Sr(NO3)2 and CO(NH2)2 were dissolved into enough deionized water to obtain a transparent solution the oxides of Eu+2 were two solution were mixed together and stirred for 4h at 70ºC. The process is summarized in a flow chart show in fig.

After stirring was completed, the precursor solution was introduced into a muffle furnace maintained at a temperature in the range of 6000C Initially, the solution boiled and underwent with the escape of large amounts of gases (oxides of carbon nitrogen and ammonia). Then spontaneous ignition occurred and smoldering combustion ensued with enormous swelling producing voluminous white foamy

ashes. The whole process was over within less than 5min after the ashes were cooled to room temperature, milled slightly and SrAl2O4: Eu+2 phosphor thus obtained.

Al(NO3).9H2o, Sr(NO3)2,

Eu2O3 dissolved in

CO(NH2)2 dissolved in

concentrated HNO3

delonized water.

Solutions mixed together and stirred for 4hat 700

combustion in a muffle furnace

Cooled to room temperature SrAl2O4:Eu2+ phosphor

3.1 INTRODUCTION since the ML is excited during the mechanical energy. That is with the stress and strain of the deforming solid is expected.

Two types of devices are generally needed for ML measurement. One for deforming the ML of samples and the other for the spectral measurement .There are various technique used for deforming the phosphor in ML measurement are. (1)Compression (Chandra and Zink, 1980a.b). (2)Bending (Alzelta et al. 1970). (3)Starching (Crasta et al. 1987). (4)Loading (Chandra and elyel 1979, Atari 1982, Atari and RAMANI 1986, Atari and Pamani 1986, Fiel et al 1986). (5)Pisten impact or impulsive (Chandra 1983). (6)Needle impact (Mayer and Pally 1965). (7)Cleaving and cutting (Longchambon 1925, Batying et al 1992, Dickinson et al 1990).

(8)Faster (Hardy et al 1979). (9)Shaking (copy Chapman and Waltor 1983a.b). (10)Air blast (Longchambon 1925, Sodomkal 1968, Meyer and Obrilcal 1969). (11)Seratching (Nakayma et al 1992). (12)Grinding and milling (Imove et al 1939). (13)Tribe or rubbing (Zhenyi et al 1995, Meyer et al 1970).

Most of the workers in the field of the ML are now a days making attempt to understand the complex processes of ML. In crushing a phosphor aften in a fairly indeterminate manner elastic, plastic and fracture processes comes into play. At the tips of developing cracks local high stresses and temperature exists and virgin surfaces are formed electrical planes by the movement of charged dislocations or even via contact potential differences betweens the crystal and crushing device. In addition the phosphor environment must be considered notably the nature and pressure of the surrounding gases. With so many uncertainties, it is not surprising that relatively little progress has been made in understanding the mechanism responsible for the ML excitation. It is still brother unclear what physical process actually takes place in the ML excitation in piezo electric crystals. The main object of the present investigation is to understand the mechanism of ML excitation in piezo electric crystal. It is believed that the measurement of the ML characteristics of the phosphor may be helpful in unpinning the secrets of excitation process of the ML. With this consideration it is planned to make some systematic measurement with respect to several parameters like intensity of ML. kinetics of ML impact velocity dependence

of ML mass dependence of ML. The present chapter reports the results obtained during impulsive excitation of ML in

3.2 EXPERIMENTAL After growth of phosphor sample of equal size were cleared from grown phosphor blocks taking size of the phosphor as equal as possible. The irradiated samples wrapped in aluminum foil were kept in dark room till ML measurement were carries out in dark room. Fig (A) and (B) show the experimental set up used for the impulsive excitation of ML. A load of particle mass and shape was dropped form different height for striking the phosphor at different impact velocity. The phosphor were reduced to a particular dimension by grinding and polishing. Then a phosphor was placed in a transparent guiding cylinder. An RCA 931 photo multiplier tube was connoted to a phosphorescent screen oscilloscope (scientific 30 Mhz Digital) storage oscilloscope (SM 340) The oscilloscope was operation in a normal triggering mode. In this oscilloscope we hold and store the trace the internal connection of photo multiplier tube are shown in fig(c). For the crystal was placed on the Lucite plate and was covered with thin aluminum tail reflects light and prevents scattering of the fragments during the impact of a moving piston out the phosphor. The rise and decay time of ML at different impact velocities were recorded by tracing the ML pulses appearing on the distance between the load to be dropped and the phosphor on the Lucite platforms the velocity of impact could be changed

from low values to 280 cm/sec . For determining the effect of load on the ML intensity the loads of different value for example 200, 400 and 800 gram were used since the pulley and the guiding cylinder used were of negligible friction the impact velocity V0 was takes as √2gh. Where g is acceleration due to gravity and h is the height through which the load is dropped freely. Since the measurements are relative the estimation does not make any difference. When the phosphor of small cross-section area as compared to the light sensitive area of photo multiplier tube the ML intensity measured is proportional to the intensity of ML intensity could not be measured absolute. In the measurement of the ML intensity was formed to be 15%.

3.3 RESULT Fig 3.3 (a) show the ML emission produced during impact of moving different height (or impact velocity). It is seen that the peak intensity of first and second peak (Im1 & Im2) increase with increasing impact velocity. However the time corresponding to first and second peak (Tm1 & Tm2) shift towards shorted time values with increase impact velocity. Fig (b) show that the total ML intensity IT defined as the area below the ML intensity versus time curve, initially increases with the impact velocity V0 and then it attains a saturation value for higher values of the impact velocity. Fig 3.3 (c) show the ultraviolet-doses dependence of IT (total ML intensity) of SrAl2O4:Eu2+ phosphor. It is seen that the values of IT increase with the irradiation doses gives to the phosphor and it seems to be saturated at highe Fig (d) show the ML spectra of SrAl2O4:Eu2+. Spectra show higher peak in the range 520.

Fig (e) show the absorption spectra of SrAl 2O4:Eu2+. The excitation wavelength for PL is 330nm. A broad band is observed at around 500-550nm in both ML spectra. The wavelength region of this broad band coincides with the green emission. This broad band is ascribable to the 4f6-5d-4f7 transition of the doped Eu2+ ion. Emission due to the 4f-4f transition of Dy3+ is not observed in the TL nor the PL spectrum.

4.1 DISCUSION The ML excitation appears in the elastic, plastic, and fracture region of strontium aluminate phosphor. The time duration of ML puses due to the motion of a single crack is in a microsecond range which is of the order of the time needed for a creak to move through the phosphor. However the time during the order of a load onto the phosphor is of the order of millisecond and depends on the impact velocity. Thus the continuous ML signal produced during the impact should be the superposition of individual ML pulses produced during the motion of many creaks in the phosphor. As such the time dependence of ML produced during the impact of a load onto the phosphor should be related to the number of mobile crack produced in the phosphor.

The linear correlation between the ML intensity and the area of newly created surfaces suggests that the atom or molecules present on the newly created surfaces are subjected to strong deformation during the movement of crack in the considerable importance in the further theoretical and experimental investigation of ML.

It has been found that the ML intensity is higher for higher values of the impact velocities. This fact indicates the creation of more surfaces at higher impact velocity. The increasing in the ML intensity with the increasing size of the phosphor also be due to the creation of more surface area (chandra 1985).

4.2 MECHANISM OF MECHANOLUMINESCENCE IN UV IRRADIATED SrAlO: Eu2+ PHOSPHOR The dislocations moving in the course of mechanical deformation are responsible for the ML of colored alkaline earth aluminet phosphor. The dislocation moving under the action of external stresses interact with the F-centers and capture electrons. If the dislocation containing electrons encounters an impurity center and luminescence arises, in which the position of peaks is identical with the position of the luminescence band of the impurity centers. Schematically the ML process can be described by the following equation. D + F ——► D − + e D − + Eu2+ ——► D +(Eu2+)* (Eu2+)* ——► Eu2+ + h where Eu2+ represent the metal ion and D⁻ represents the dislocation containing the anion vacancy left behind the F-center.

The process described above is able to explain ML only n the deformation region. The ML in the post deformation can be realized in principle by Auger process. One may assume that the moving dislocation transfer the electrons from the F-centers to holes. And their subsequent recombination may not only result the light emission but some of them may also result Auger ionization of other electron center. The absorbed ions for instance, can play the role of such trap. The recombination between deep traps and the electrons carried by dislocation on the SrAl2O4 surface

can also cause the Auger ionization of other dislocation electrons to the conduction band bottom.

It has been found that the ML intensity increases with radiation doses given to the phosphor and then it attains a saturation value for the nigher values of ultraviolet. When the phosphor is irradiated electron hole pairs are formed some of the electrons get trapped in the negative ion vacancies, and they formed color centers. Initially the number of color center increases with radiation doses given to the phosphor and thereby, the ML intensity also increases with radiation doses. However, for long duration of irradiation of the phosphor, the recombination between electron and hole takes place and consequently the density of color center in the phosphor attains a saturation value. As a matter of fact, the ML intensity also attains a saturation value for high radiation doses given to the phosphor.

4.4 CONCLUSION The conclusion drawn from the studies on the impulsive excitation of ultraviolet Eu2+ doped SrAl2O4 phosphor are summarized as below • During the impulsive deformation of ultraviolet irradiated Eu2+ doped SrAl2O4 phosphor; two peaks are observed in the ML intensity versus time curve. The first peak Im1 which appears in the deformation region is always greader then the intensity of the second peak Im2 which lies in the post deformation region. • For different impact velocity, ML intensity increases with velocity and total ML intensity increase attains a saturation value for higher impact velocity. • The ML intensity of SrAl2O4 :Eu2+ phosphor increase linearly with increase in mass of load. • Initially the ML intensity increase with ultraviolet does and for larger irradiation dose. It gets saturated.

REFERENCES B.P.CHANDRA : MECHANOLUMINESCENCE IN; LUMINESCENCE OF SOLIDS ED. D.R. VIJ (NEW YORK:PLENUM) PP 361-389 (1998). ZUOLING Fu, SHIHONG ZHOU, YINGING Yu, SIUAN ZHANG : Chemical physics letters 285-289 (2004). HARISH CHANDER, D.HARANATH, VIRENDRA SHANKER, POOJA SHARMA : Synthesis of nanocrystals of long porsisting phosphor modifid combustion techanique. KASHINATH C.PATIL, S.T. ARUNA, TANU MIMANI : Combustion synthisis an update (2002). JORMA HOLSA, TANELI LAAMANEN, MIKA LASTUSAARI, JANNE NIITTYKOSKI, PAVEL NOVAK : Electronic stucture of the SrAl2O4 : Eu2+ persistent luminescence material (2008). B.P.CHANDRA, RADI J.EFFECTS AND DEFFECTS SOLIDS (1996). B.P.CHANDRA AND ELYAS, M.(1977) : Indian J.Pure Appl.Physics;15,744. B.P.CHANSDRA,VERMA R.D., KHOKHAR MSK, BATRA DESHMUKH B.T. : ML excitation in ahc and colouration decay in micro-crystalline powders ; pramana J. phy. Vol. 25, DSE 1985.

KHER R.S., B.P. CHANDRA, SARMA P. : Studies of the ML produced during in ultravoilet irradiated divalent, impurity doped SrAl2O4 phosphor. KHRR R.F., N.BRAHME, BANERJEE M., DHOBLE J.T. & KHOKHER M.S.K. : Deformation luminescence (2006). N.RAJPUT, S.TIWARI & B.P.CHANDRA : Indian journal of physics 569-573 (2004). N.RAJPUR, S.TIWARI & B.P.CHANDRA : NCLA (2006). WOLFF, G.,GROSS, G. & STRANSKI, I.N.(1952) : Z. Eletrochm ;58,420 (1952) HUAJIE SONG & DONGHUA CHEN. B.P.CHANDRA : Luminescence induced by elastic deformation of SrAl2O4 : Eu , Dy crystals. MORITO AKIYAMA, CHAO-NAN Xu, MASANORI TAIRA, KAZUHIRO NONAKA & TADAHIKO WATANABE : Visualization of stress distribution using ML from Sr3Al2O6 : Eu and the nature of the luminescence mechanism.(1999). N.KHOSROVANI & A.W. SLEIGHT ,INT.J.INORG.MATER 1 : 3-11 (1999). J.S.O. EVANS & T.A.MARY,INT J.INORG.MATER 2 : 143-151 (2000).