METHOD FOR SECURING VALUE DOCUMENTS USING STORAGE PHOSPHORS

Abstract

A method for checking an authenticity feature having an optical storage phosphor, to an apparatus for checking, an authenticity feature and to a value document having an authenticity feature. The authenticity feature has an optical storage phosphor. In one step, the optical storage phosphor is subjected to at least one query sequence, respectively comprising at least a first readout process and a second readout process. At least a first and a second readout measurement value are captured, which respectively are based on the detection of an optical emission in response to the respectively first or the respectively second associated readout process. A readout measurement value time series is created and is respectively associated with the at least one query sequence, comprising at least the first readout measurement value respectively associated with the first readout process and the second one respectively associated with the second readout process.

Claims

1.-24. (canceled)

25. A method for checking an authenticity feature having an optical storage phosphor, comprising the steps of: a. capturing at least a first measurement value, including a storage charge and/or a light emission of the optical storage phosphor; b. subjecting the optical storage phosphor to at least one charging process; c. capturing at least a second measurement value, including a storage charge and/or a light emission of the optical storage phosphor; and d. quantitatively determining an effect of the charging process on the optical storage phosphor from the at least one first and second measurement value.

26. The method according to claim 25, wherein the optical storage phosphor has light centers and trap centers, wherein, preferably, charge carriers present in the storage phosphor are at least partially transferred to the trap centers by the charging process in step b.

27. The method according to claim 25, wherein the method comprises at least one readout process and the first and/or second measurement value are captured independently of a readout process.

28. The method according to claim 25, wherein the method comprises at least one readout process and the at least first and/or second measurement values are captured as first and/or second readout measurement values which are accordingly captured based on a detection of a light emission in response to at least one readout process, wherein, preferably, the first measurement value is captured as a readout measurement value based on a detection of a light emission in response to a first readout process and the second measurement value as a readout measurement value based on a detection of a light emission in response to a second readout process.

29. The method according to claim 26, wherein the method comprises at least one readout process and the first and/or second measurement value are captured independently of a readout process; wherein by the at least one readout process at the trap centers, stored charge carriers of the trap centers are excited and they transition to the light centers, the charge carriers radiantly relaxing at the light centers.

30. The method according to claim 27, wherein the method has at least one query sequence, comprising at least two readout processes, wherein from the first readout process a first readout measurement value and from the second readout process a second readout measurement value are captured; and the method comprises the steps of: d. creating a readout measurement value time series respectively associated with the at least one query sequence, comprising at least the first readout measurement value respectively associated with the first readout process and the second one respectively associated with the second readout process; and e. evaluating the readout measurement value time series respectively associated with the query sequence for determining a dynamic behaviour from the readout measurement value time series under the respectively associated query sequence.

31. The method according to claim 25, wherein a charging process comprises at least one charging pulse or a continuous charging intensity-modulated over time.

32. The method according to claim 31, wherein the charging pulse has a wavelength region of 240 nm and 550 nm, and/or the pulse duration in a region of 1 s and 100 ms.

33. The method according to claims 30, wherein the method comprises two query sequences which respectively comprise at least a first readout process and a second readout process and wherein preferably the captured readout measurement values are different for each query sequence.

34. The method according to claim 30, wherein in step d) the evaluating of the readout measurement value time series is effected quantitatively in order to determine at least one characteristic memory property of the optical storage phosphor.

35. The method according to claim 27, wherein each readout process comprises at least one readout pulse or a continuous readout intensity-modulated over time.

36. The method according to claim 35, wherein the readout pulse has a centroid wavelength from a wavelength region of 360 to 1200 nm and/or the pulse duration is in a region of 1 s and 100 ms.

37. The method according to claim 30, further comprising at least one charging sequence comprising at least one first charging process for subjecting the optical storage phosphor temporally before the at least one query sequence.

38. The method according to claim 27, comprising a repeated and/or respectively alternating succession of the at least one charging process and the at least one readout process.

39. The method according to claim 34, wherein the at least one characteristic memory property is selected from: persistence, memory depth, memory strength, sensitivity, specificity, exchangeability, association, continuity, latency, saturation, isolation, charging speed and/or readout speed.

40. The method according to claim 34, wherein the step of evaluating the readout measurement value time series for at least one characteristic memory property of the optical storage phosphor comprises a determination of the shape of the temporal course of the curve of the readout measurement value time series or a determination of parameters which describe the temporal course of the curve of the readout measurement value time series.

41. The method according to claim 25, wherein at least one charging process differs from another charging process at least in the wavelength and/or intensity and/or pulse length.

42. The method according to claim 31, wherein at least a first charging pulse differs from another charging pulse at least in the pulse duration and/or pulse interval duration.

43. The method according to claim 25, wherein by subjecting the optical storage phosphor to at least one charging sequence and/or at least one preparation step a threshold emission is set.

44. The method according to any claim 28, wherein by the readout measurement value time series of at least two readout measurement values the charging speed of the optical storage phosphor is determined.

45. The method according to claim 25, comprising the step f matching the determined dynamic behaviour of the readout measurement value time series with at least one reference, as well as g. recognizing the authenticity of the authenticity feature as a function of the matching f.

46. The method according to claim 25, comprising the step h. subjecting the optical storage phosphor to at least one thermalizing sequence.

47. An authenticity feature having an optical storage phosphor for checking the authenticity of the authenticity feature with a method according to claim 25, wherein the optical storage phosphor has a charging spectrum with at least one distinctive spectral structure which in the charging efficiency is configured varying with the wavelength, wherein the readout spectrum has at least one local minimum, in which the charging efficiency is reduced by at least 10% in comparison to the flanking maxima.

48. A value document having at least one authenticity feature according to claim 47.

Description

FIGURES

[0276] The invention is hereinafter described in connection with FIG. 1 to FIG. 12. In the Figures there are shown:

[0277] FIG. 1: a measurement sequence of three pulses P1, P2, and P3, three pulse forms being represented exemplarily, rectangle form, impulse form and modified sawtooth form;

[0278] FIG. 2: different charging speeds of three substances (substance I, substance II, substance III);

[0279] FIG. 3: normalized signal course under a pulse pair (first pulse red followed by pulse NIR) together with exponential adaptation of the measuring signal;

[0280] FIG. 4: excitation spectrum, emission spectrum and readout spectrum of substance I;

[0281] FIG. 5: excitation spectrum, emission spectrum and readout spectrum of substance II;

[0282] FIG. 6: excitation spectrum, emission spectrum and stimulation spectrum of substance III;

[0283] FIG. 7: measurement sequence 16(Q), readout repeated 16 times with readout pulse Q and the associated readout curve for substance I together with the exponential adaptation to the envelope;

[0284] FIG. 8: substance I under the alternating sequence succession of the 12 red or NIR-light pulses 12(red NIR) and the readout curve;

[0285] FIG. 9: substance I the value of the signal maxima for each pulse for the sequence 12(red NIR);

[0286] FIG. 10 a-c: examples of exchangeability: 1.sup.st row substance I, 2.sup.nd row substance II, 3.sup.rd row substance III; additionally, the maximum signal amplitudes for each readout pulse are respectively marked (rhombuses);

[0287] FIG. 10a: employed measurement sequences 8(RR *), readout curves for substances

[0288] FIG. 10b: employed measurement sequence 16R, readout curves for substances I-III;

[0289] FIG. 10c: employed measurement sequence 16R*; readout curves for substances I-III;

[0290] FIG. 11: comparison of the distinguishability measure U for substance I, substance II and substance III, calculated under the sequences 8(RR *), 16R and 16R*;

[0291] FIG. 12: comparison of the one-sided and uniform distance for substance I, substance II and substance III as a proof of exchangeability: Only for substance I both measures have small values. For substance I the readout pulse R and R* are thus exchangeable also on these measures.

EMBODIMENT EXAMPLE 1

[0292] Substance I: Strontium Sulphide Doped with Copper and Bismuth Manufacture 19.93 g SrCO3, 0.03 g Bi.sub.2O.sub.3 and 0.01 g CuS were mixed carefully and poured into a corundum crucible. The mixture was overlaid with 24 g of a 1:1 mixture of elementary sulphur and Na.sub.2CO.sub.3 and covered with a lid. Subsequently, the material was annealed at 900 C. for 6 h. The sintered material was crushed, and ground in a swing mill. The finished product is present after a final heating step (12h at 550 C.). The associated spectra are represented in FIG. 4.

[0293] Substance II: Strontium sulphide doped with europium and samarium Preparation analogous to substance I. The associated spectra are represented in FIG. 5.

[0294] Substance III: Strontium aluminate doped with europium and thulium Preparation follows Katsumata, T., et al Trap Levels in Eu-doped SrAl.sub.2O.sub.4 Phosphor Crystals Co-Doped with Rare-Earth Elements. J.A. Ceram. Soc. In 2006, Vol. 89, 3, P. 932-936. The associated spectra are represented in FIG. 6.

EMBODIMENT EXAMPLE 2

Measurement Sequence, Readout Repeated 16 Times with Readout Pulse Q, 16(Q)

[0295] In the first example, the excited substance I (excitation was effected with a blue light pulse) is read out repeatedly 16 times with the same readout pulse (designated as Q) and the occurring signal in the region of 490 nm to 550 nm is measured with an avalanche photodiode at 2 MHz sampling frequency and recorded as a readout curve. The parameters describing the readout pulse are summarized in the following table.

TABLE-US-00001 TABLE 1 Parameters of the readout pulse red Parameter Readout pulse Q Wavelength of the laser diode 638 nm Current 500 mA Pulse duration 4 s Pulse distance 6 s

[0296] In FIG. 7 the pulse train of the readout pulse (vertical axis on the right) and the readout curve (vertical axis on the left) are represented versus time. The charging pulse (laser diode 450 nm, current 800 mA, duration 200 s) was effected outside the represented data (at the time t=0). In the measurement data additionally the exponential adaptation to the envelope, beginning with the 2nd pulse, is entered as a dashed line. Substance I additionally has a certain afterglow which becomes visible in the signal rise from the first to the second pulse of the pulse train. This afterglow is superimposed on the OSL signal. This is a very specific property of the system described here including substance I, the measuring apparatus and the measurement sequence used, which property is based on the strong interlacing of these components of the authenticity system. This is advantageously used for the authenticity evaluation of the marked item.

[0297] For the evaluation of the readout curve, the lifetime from the exponential adaptation to the envelope can be used, this value is 341.3 s here. Moreover, the emptying ratio can be used, which is defined here via the difference of the maximum signal intensity of the a.sup.th pulse at the beginning of S(a) and of the b.sup.th pulse near the end of the sequence S(b), weighted with the sum of these intensities,

[00001]$=\frac{S\left(a\right)-S\left(b\right)}{S\left(a\right)+S\left(b\right)}.$

In the represented case, for a=2, b=15 there results the value =0.198.

[0298] Furthermore, for the evaluation, the exact shape of the readout curve can compared with a reference curve, or selectively further characteristic aspects of the curve, such as e.g. the build-up or decay times of the intensities of the single pulses or the respective afterglow portion can be compared with corresponding reference values.

Embodiment Example 3: Measurement Sequence, Alternating Readout 12 (red NIR)

[0299] In this example, the charged substance I is exposed to the sequence 12 (red NIR) and the occurring signal in the region of 500 and 550 nm is measured: initially, the substance is charged with the process W (the charging pulse ends at the time t=300 s), after a waiting period (delay, 2 ms) one reads out at first with the process red, then with the process NIR. The waiting period ensures that no afterglow contributes to the signal. A different (in particular shorter) waiting period is possible, but leads to a different readout curve because of the afterglow and other relaxation effects. Ultimately, a measurement sequence with a different waiting period represents a different measurement sequence. This succession of the readout pulses is repeated 12 times. The processes are defined in Table 2 and represented in FIG. 8. By way of example, the authenticity analysis is effected on the basis of several measure values.

TABLE-US-00002 TABLE 2 Parameters of the charging pulse W and the readout pulses red and NIR Processes and parameters W red NIR Wavelength 455 nm 638 nm 853 nm Current 1000 mA 800 mA 1000 mA Rel. intensity after attenuator 100% approx. 40% 100% Pulse duration 80 s 2.5 s 2.5 s Pulse distance 2 ms 11.25 s 11.25 s

[0300] The storage properties used in this invention as an authenticity feature can be determined with the help of the readout curve. For this purpose, there are ascertained, for example, the signal maxima (or the integral of the signal for each pulse) of the processes red and NIR and represented as a time series:

[0301] As visible in FIG. 9, falling curves are the result for each of the processes. The quantities red(n) or NIR(n) designate the maximum signal, the quantities sum_red(n) or sum_NIR(n) the integrated signal associated with the n.sup.th application of the respective process. Table 3 summarizes some possible measure values of the invention and the associated results in this example.

TABLE-US-00003 TABLE 3 Examples of characteristic measure values and their evaluation for substance I Result Comment [00002]${}_{\mathrm{rot}}=\frac{\mathrm{rot}\left(1\right)-\mathrm{rot}\left(12\right)}{\mathrm{rot}\left(12\right)}$ 0.6 Emptying ratio for the readout pulse red [00003]${}_{\mathrm{NIR}}=\frac{\mathrm{NIR}\left(1\right)-\mathrm{NIR}\left(12\right)}{\mathrm{NIR}\left(12\right)}$ 1.0 Emptying ratio for the readout pulse NIR [00004]$b=\frac{1}{11}.Math.\underset{n=2}{\overset{12}{.Math.}}.Math.\frac{\mathrm{NIR}\left(n\right)}{\mathrm{rot}\left(n\right)}$ 1.83 Mean value of the signal intensity ratios of the two readout processes red and NIR. The first pulse pair is ignored in order to intercept possible transient behaviour. The ratio NIR(n)/red(n) for n > 2 is near 1.83 within 5% deviation. [00005]$B=\frac{1}{11}.Math.\underset{n=2}{\overset{12}{.Math.}}.Math.\frac{\mathrm{sum\_NIR}.Math.\left(n\right)}{\mathrm{sum\_rot}.Math.\left(n\right)}$ 1.66 Mean value of the ratio of the signal intensities of the two readout processes red and NIR, integrated over the respective pulse. The first pulse pair is ignored in order to intercept possible transient behaviour. The ratio sum NIR (n)/sum red(n) for n > 2 is near 1.66 within 5% deviation. [00006]$d=\frac{\mathrm{NIR}\left(2\right)-\mathrm{NIR}\left(12\right)}{\mathrm{rot}\left(2\right)-\mathrm{rot}\left(12\right)}$ 2.0 Ratio of the signal intensity differences of the two readout processes red and NIR. The first pulse pair is ignored in order to intercept possible transient behaviour. [00007]$D=\frac{\mathrm{NIR}\left(2\right)-\mathrm{rot}\left(12\right)}{\mathrm{rot}\left(2\right)-\mathrm{NIR}\left(12\right)}$ 15.2 A possible measure for the variability of the effect of the two readout processes red and NIR. The first pulse pair is ignored in order to intercept possible transient behaviour.

[0302] Besides the entire readout curve, also each pulse can be viewed. The build-up or decay behaviour of a single pulse gives characteristic information about the time behaviour of the light center as well as possibly occurring afterglow. FIG. 3 shows the normalized signal course under a pulse pair red/NIR, i.e. first pulse red followed by pulse NIR together with exponential adaptations of the measuring signal to the part of the readout curve in which respectively the readout pulse is off and the signal has substantially decayed. From these data, the exponent of adaptation can be utilized as a further measure value. Alternatively, intensity ratios can be formed at different times and used as a measure for the characteristic time behaviour of the luminescence.

TABLE-US-00004 TABLE 4 Examples of a characteristic measure value which is based on luminescence decay times and afterglow and the evaluation thereof for substance I Result Comment Exponential adaptation to 122144 This quantity describes the signal pulses normal- s.sup.1 (NIR) the luminescence lifetime ized to the maximum of NIR, 114967 or also portions of the as of a distance of 2.5 s s.sup.1 (red) afterglow from the pulse maximum, the exponent thereof

EMBODIMENT EXAMPLE 4

Exchangeability and Libraries

[0303] In this example, substance I is incorporated as an authenticity feature in a bank note paper, the substances II and III represent an alternative substance and an imitator. Substance I and II noticeably differ spectrally, while substance I and III have very similar emissions.

[0304] At first, two readout pulses are established for the feature substance I, which are exchangeable in their effect, namely readout pulse R and R*. The parameters of the two readout pulses are summarized in the Table 5 below. Exchangeability means that the order of the two readout pulses can be exchanged within a sequence without the readout curve being changed noticeably.

TABLE-US-00005 TABLE 5 Parameters of the readout pulse R and R* R R* Wavelength 638 nm 853 nm Current 800 mA 1000 mA Rel. intensity after attenuator approx. 40% 100% Pulse duration 2 s 2 s Pulse distance 8 s 8 s

[0305] Suitable measurement sequences which include R and R* can test the exchangeability for the proof of authenticity. An example of such sequences is the sequence 8 (R R *) in which R and R* alternate. The sequence begins with R and comprises a total of 16 readout pulses. The measurement sequence and the readout curve for the substances I, II and III charged before (by a blue light pulse) under this sequence are represented in FIG. 10a to c.

[0306] While the readout curve for substance I shows a uniform fall of the intensity, the readout curve for substance II and in particular for substance III is clearly modulated. If one views also the equally long measurement sequences which include only one of the two readout pulses, namely 16R and 16R*, the readout curves for all three substances (I, II, III) behave in a uniformly falling fashion.

[0307] For the proof of authenticity, distinguishability measures are defined. Such a measure describes, to what extent two pulses within a sequence are distinguishable in their effect. For the measurement sequence 8(R R *) the distinguishability measure U is determined as follows: At first, for each readout pulse the value of the associated maximum of the readout curve is determined (marked as rhombuses in FIG. 10a to c). This value is designated as a pulse intensity P.sub.n, the index n designating the n.sup.th pulse of the measurement sequence. For the viewed n.sup.th pulse of the measurement sequence it is calculated how far it is away from the geometric mean of the pulse intensities of the neighboring pulses of the measurement sequence, i.e.

d.sub.n={square root over (P.sub.n1P.sub.n+1)}P.sub.n,

where n is from 2 to 15, because the first and the last pulse have no neighbours. The standard deviation of the values d.sub.n is designated as the distinguishability measure U. In FIG. 11, there is respectively represented the distinguishability measure U for the measurement sequence 8 (R R *) for the substances I, II and III. For comparison, moreover, the value of the distinguishability measure U is respectively drawn in for the sequences 16R and 16R*. Substance I from all three measurement sequences has a small distinguishability, U (substance I) <0.1. The two other substances have a distinguishability U>0.3 under the measurement sequence 8 (R R *). For substance II and substance III, the readout pulse R and R* are not exchangeable in their effect.

[0308] Besides, for the measurement under the sequence 8 (R R *) there is also used the sequence 16 R* and/or 16R. The readout curve under 16 R* serves as an estimator for the readout curve and thus for the pulse intensities under the measurement sequence 8 (R R *). For the proof of authenticity, the one-sided distance or the uniform distance of the readout curves is determined. For this purpose, first the pulse intensities of the readout curves are normalized such that respectively the pulse intensity of the first readout pulse of a measurement sequence is set to the value 1. The such normalized pulse intensity of the n.sup.th pulse under a measurement sequence is designated as .

[0309] The one-sided distance here results from

[00008]$\mathrm{.Math.}=\sqrt{\underset{n=1}{\overset{16}{.Math.}}.Math..Math.{\left({\hat{P}}_n\left[8.Math.\left({\mathrm{RR}}^{*}\right)\right]-{\hat{P}}_n\left[16.Math.R^{*}\right]\right)}^2}$

[0310] The uniform distance here is calculated via

[00009]$=\frac{1}{16}.Math.\underset{n=1}{\overset{16}{.Math.}}.Math.\sqrt{.Math.{\left({\hat{P}}_n\left[8.Math.\left({\mathrm{RR}}^{*}\right)\right]-{\hat{P}}_n\left[16.Math.R^{*}\right]\right)}^2+{\left({\hat{P}}_n\left[8.Math.\left({\mathrm{RR}}^{*}\right)\right]-{\hat{P}}_n\left[16.Math.R^{*}\right]\right)}^2}$

[0311] Both measures ultimately describe how readily the effect of the readout pulses R and R* are exchangeable, the measurement sequences 16R and 16R* providing estimators for the measurement sequence 8 (R R *).

[0312] The FIG. 12 summarizes the values of the one-sided and uniform distance for substance I, substance II and substance III, calculated as stated above with the data of FIG. 10a to c. Only for substance I both measures have small values (<0.1; <0.1). Only for substance I, the readout pulses R and R* are exchangeable in their effect also on these measures.

[0313] This approach can be generalized, and not only alternating pulse trains but also more complicated measurement sequences can be used. Exchangeability can be also defined for more than two different readout pulses. For the proof of authenticity, suitable measurement sequences are thus summarized to reference libraries. Here, for example the mentioned measurement sequences 8 (R R *), 16R and 16 R* belong to one reference library. A further sequence of this reference library is summarized from groups of the readout pulses R and R*, whereby in the measurement sequence at first R is executed eight times and afterwards R* is executed eight times, i.e. 8R8R*. Also for this measurement sequence, a distinguishability measure can be defined and/or the one-sided and/or the uniform distance can be calculated and be used for the proof of authenticity. Furthermore, the reference library includes further measurement sequences of the length 16, different permutations of the succession of R and R* being used.

[0314] As needed, short and long measurement sequences expand the reference library, for example, the sequence RRR* or R*RR are also part of the library as 100R, 100R*, 100(RR*), which can be utilized, for example, for the proof of authenticity in different employment scenarios, e.g. quality assurance of the feature, of an intermediate product or of the bank note without disclosing the evaluation process running in the machine bank note processing. Alternatively, likewise, different check locations of the banknotes (e.g., POS cash point versus central banks) may use different measurement sequences of the reference libraries.

[0315] As needed, measurement sequences using other readout pulses are added to the reference library. These readout pulses include, for example, those with longer pulse duration (10 s, 100 s) and/or with other wavelengths (for example, 488 nm, 532 nm, 658 nm, 758 nm, 808 nm, 915 nm, 980 nm) and/or other intensities of the light sources. With these pulse sequences (which are formed in analogy to the mentioned ones and/or other pulse orders) it is ensured that a substance can be reliably proven on different sensors. In particular, the reference library also includes measurement sequences of at least three different readout pulses, for example, the sequence 4 (SRR*), the readout pulse S being defined by the parameters in the subsequent Table 6: Parameters of the readout pulse.

TABLE-US-00006 TABLE 6 Parameters of the readout pulse S Wavelength 1064 nm Current 1000 mA Rel. intensity after attenuator approx. 40% Pulse duration 4 s Pulse distance 8 s

[0316] This additional readout pulse serves for the differentiation of substance I and substance II in the reference library and causes a strong signal for substance II, while substance I delivers only a weak signal.

EMBODIMENT EXAMPLE 5

Superimposed Readout Pulses and Third Readout Pulse

[0317] In a further example, substance I is incorporated into a suitable transparent lacquer system and doctored onto a carrier foil (10 weight percent of feature powder in the lacquer, wet film thickness 50 m).

[0318] In a reference library three query sequences are deposited.

[0319] As a first query sequence a pulse train is used in which at first 6 pulses of the type Q are employed, as in Example 2. Subsequently, the authenticity feature is illuminated with three further pulses of the type Q superimposed by a long lasting pulse L (wavelength 780 nm, energization 1000 mA, pulse duration 30 s, pulse distance 30 s). The negative pulse distance ensures the superimposition. Via an attenuator the illuminance is set such that the signal intensity caused by the first pulse of the superimposition is twice as large as the signal intensity caused by the first pulse Q of the query sequence. In a proof of authenticity this is checked and the readout speeds are determined for both parts of the query sequence. During the superimposition the authenticity feature can be read out substantially faster.

[0320] In comparison to the authenticity feature, substance II and substance III have a ratio of the signal intensity of the first pulse of the superimposition to the signal intensity of the first pulse of the query sequence which deviates from the factor 2. The influence of the superimposition on the readout speed is substantially lower for substance II and substance III.

[0321] As a second query sequence the alternating sequence 8 (RR *) of Example 4 is deposited. The proof of authenticity follows Example 4.

[0322] As a third query sequence an alternating succession 5 (RTR*) is employed. Pulse T uses the same illumination source as L (780 nm), but is defined as a short pulse (pulse duration 1 s, pulse distance 4 s). Again, the pulses R and R* are exchangeable for the authenticity feature. Pulse T does not disturb the exchangeability.

EMBODIMENT EXAMPLE 6

Different Effects of Charging Pulses

[0323] In FIG. 2, the different charging speeds of the three OSL substances, substance I, substance II and substance III, are evaluated. For this purpose, respectively the same succession of readout pulse and charging pulse repeated ten times is composed into one sequence and the effect thereof on the three OSL substances is compared.

[0324] The readout pulse measures here the effect of the previously running charging pulse. From the maxima of the readout pulses there thus results an evaluateable curve for the charging speed of these substances. Here, one recognizes significant differences in the effect of the charging pulses on the substances I, II or III: While the charging pulses show no significant effect on substance I, a significant increase of the intensity of the optical emission is observed for substance II in response to the respectively associated readout process. With a suitable quantitative evaluation the substances II and III can also be differentiated from each other with the help of their charging behaviour.

EMBODIMENT EXAMPLE 7

Charging Processes with Different Efficiency

[0325] The OSL substances substance I and substance II are subjected to a repeated sequence of

5 charging pulse 280 nm
5 readout pulse 900 nm
4 charging pulse 450 nm
4 readout pulse 900 nm.

[0326] Here, for substance I and for substance II there is observed a respectively quantitatively different charging effect for the two charging processes at 280 nm or at 450 nm, with the help of which the two substances can be differentiated.

[0327] For a person skilled in the art it is a matter of course that the mentioned examples are stated merely exemplarily and, if possible, other combinations and values ranges, as stated, are conceivable. The stated examples should therefore not be read as limiting, but can also be read along in combination with the different features stated herein.

LIST OF LITERATURE

[0328] 1. Chen, R. and McKeever, S. W. S. Theory of thermoluminescence and related phenomena. Singapore: World Scientific Publishing, 1997.

[0329] 2. Garlick, G. F. J. Phosphors and Phosphorescence. Reports on Progress in Physics. 1949, Vol. 12, p. 34-55.

[0330] 3. McKeever, S. W. S. Thermoluminescence of solids. Cambridge: Cambridge University Press, 1988.

[0331] 4. Yukihara, E. G. and McKeever, S. W. S. Optically Stimulated Luminescence. s.1.: Wiley, 2011.

[0332] 5. Ronda, C. Luminescence: From Theory to Applications. Weinheim: Wiley-VCH, 2008.

[0333] 6. Urbach, F., Pearlman, D. and Hemmendinger, H. On Infra-Red Sensitive Phosphors. Journal of the Optical Society of America. 1946, Vol. 36, 7, p. 372-381.

[0334] 7. Katsumata, T., et al., Trap Levels in Eu-doped SrAl2O4 Phosphor Crystals Co-Doped with Rare-Earth Elements. J. A. Ceram. Soc. In 2006, Vol. 89, 3, P. 932-936.