Vol.5, No.11, 1183-1188 (2013) Natural Science
http://dx.doi.org/10.4236/ns.2013.511144
Possibility of using the beet dyes as a laser
gain medium
Abdelaziz Hagar Abdelrahman1,2*, Malik A. Abdelrahman3,4, Mohammed Khaled Elbadawy3
1Laser Institute, Sudan University for Science and Technology (SUST), Khartoum, Sudan;
*Corresponding Author:
2Physics Department, Collage of Science & Arts, Muznab, Qassim University, Qassim, KSA
3Chemistry Department (SUST), Khartoum, Sudan
4Chemistry Department, Collage of Applied Medical Sciences, (TURUBA), Taif University, Taif, KSA
Received 27 July 2013; revised 27 August 2013; accepted 4 September 2013
Copyright © 2013 Abdelaziz Hagar Abdelrahman et al. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Nowadays the dye lasers play as an important
tool and are used in many applications including
spectroscopy, medicine and dermatology. This
research was carried out to study the possibility
of using the beet dyes as a laser gain medium.
The fluorescence quan tum y ield was determine d
by the comparative method with rodamine b as
an organic dye standard. The value of the fluore-
scence quantum yield was found about (0.14)
and the fluorescence quantum yield was devel-
oped until reaching about (0.323). The increas-
ing of fluorescence quantum yield of dye solu-
tion as a result of increasing the viscosity of
solvent was observed clearly. The study con-
cluded that the beet dyes are so sensitive to
fluorescence and it is very suit able to be used as
a laser gain medium.
Keyw ords: Beets; Lasing; Solvents; Quantum Yield
1. INTRODUCTION
From the mid 60s, dye lasers have been attractive
sources of coherent tunable radiation because of their
unique operational flexibility [1]. Light amplification by
stimulated emission of radiation, that is lasers, has be-
come an important tool in chemistry and many sciences. A
dye laser can be defined as a laser utilizing dye [2]. Some
of the most popular and heavily investigated are the rho-
damines and coumarins. Dye lasers have many advan-
tages over their liquid counterparts. They are nontoxic,
nonflammable, and can be engineered to be rugged and
compacted by eliminating the dye flow hardware that is
necessary in a liquid system. Liquid dye lasers rely on dye
flow through the laser cavity to avoid thermal problems
and the buildup of photo degradated dye molecules which
decrease the lasing efficiency [3].
The knowledge of fluorescence quantum efficiency of
organic dyes is important in selecting efficient dye laser
media [4]. Organic dyes dissolved in suitable liquid sol-
vent have found wide application in laser technology
serving as an active gain medium for generation of co-
herent tunable radiation [5].
A dye laser is a laser which uses an organicdye as the
lasing medium, usually as a liquidsolution. For effective
performance, dye molecules should have strong absorp-
tion at excitation wavelength and minimal absorption at
lasing wavelength. Applications of lasers are wide and
varied today. They are found in communication tech-
niques, microsurgery and medicine [6].
2. QUANTUM YIELD
The quantum yield of a radiation-induced process is the
number of times that a defined event occurs per photon
absorbed by the system. Thus, the quantum yield is a
measure of the efficiency with which absorbed light
produces some effect [7].
Quantum yield is essentially the emission efficiency of
a given fluoro chrome. Since not all photons are absorbed
productively, the typical quantum yield will be less than 1
[8].
The fluorescence quantum yield is defined as the ratio
of the number of photons emitted to the number of pho-
tons absorbed or we can written as .[9].
number of photons emitted
number of photons absorbed
QY  (2.1)
In comparative method, the same for different sample
solutions compared under identical conditions of excita-

A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188
1184
tion [9]. We may re-write Equation (2.1) as:

 
number of photons detected
fraction of light absorbed
QY
F


 (2.2)
where α and β are constants related to the fraction of
emitted light entering the light collection optics of the
fluorimeter and the intensity of the excitation source at the
excitation wavelength, respectively. In this equation, the
number of photons detected is the integrated area under
the corrected fluorescence spectrum and the fraction of
light absorbed (F) is obtained from the absorbance at the
excitation wavelength by;
110
D
F  (2.3)
where (D) defined as an optical density of a medium is the
measure of its transmittance for a radiation of particular
wavelength. The relationship between the optical density
and transmittance (T) is an inverse, which expressed as
[10].


10
log 1DT
(2.4)
Hence, for sample X, we can write:
x
x
x
A
QY
F


 (2.5)
where Ax is the integrated area under the corrected fluo-
rescence spectrum. For a “standard” material, S, for which
the quantum yield of fluorescence is already known, we
can similarly write:
s
s
s
A
QY
F


 (2.6)
Comparative measurements on solutions of sample X
and a suitable standard, S, can then be used to estimate the
fluorescence quantum yield of X by dividing Equation
(2.4) by Equation (2.5):
x
xs
s
sx
QYA F
QYA F
 (2.7)
where upon the unknown constants α and β cancel out.
Hence:
x
s
xs
s
x
A
F
QY QY
A
F




(2.8)
where all terms on the right hand side of Equation (2.7)
are known. It is assumes that measurements on solutions
of X and S are made under identical conditions of excita-
tion wavelength and aperture settings. If different solvents
are used for X and S, then Equation (2.7) should be further
modified to allow for the effect of refractive index on the
relative amount of fluorescence collected by the fluori-
meter detection optics. The final equation for estimation
of fluorescence quantum yields by the Comparative
Method then becomes:
2
xs x
xs
sx s
AF n
QYQY AF n






(2.9)
where the ns and nx are the refractive indices of the sol-
vents used for the two solutions fluorescence spectra are
always fully corrected using the installed correction
function of the Jobin Yvon Fluorolog spectro fluorimeter.
This function corrects for the variation with wavelength of
the sensitivity of the photomultiplier and the spectral
characteristics of the detection optics (gratings, mirrors,
etc.) [9].
In practice at nanotechnologies, solutions of quantum
yield material are compared with solutions of organic
fluorophores of known quantum yield under the same
conditions of excitation. Absorbance’s of all solutions are
adjusted so as to be preferably in the range (0.02 - 0.07)
and not greater than ca. 0.1 at the excitation wavelength. If
possible, it is best to arrange for the absorbencies of the
sample and standard solutions to be the same (or nearly
the same) at the exciting wavelength. Organic controls
that have been used are as shown in Table 1 [9].
3. CHOICE OF SOLVENT
Prepared laser dye solutions usually contain very small
quantities of dye. Typical dye concentrations are 10−2 to
10−5 molar. For this reason, the solvent in which the dye is
dissolved plays an important role when defining physical
properties and potential hazards.
Table 1. Quantum yields determined by this method are reliable to about ±10%.
Standard Solvent QY Fluorescence max (nm) Useful excitation range (nm)
9.10-diphenylanthracene Ethanol 0.90 406 - 4.27 320 - 370
Coumarin 1 Ethanol 0.70 450 320 - 370
Rhodamine 123 Ethanol 0.96 535 440 - 490
Rhodamine 6G Ethanol 0.95 560 450 - 500
Sulphorhodamine 101 Ethanol 0.95 600 500 - 550

A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188 1185
Lasing wavelength and energy are very sensitive to the
choice of solvent. Most laser dyes are polar molecules,
and excitation into their lowest-lying singlet state is ac-
companied by an increase in the dipole moment. Ac-
cordingly, solvent polarity plays an important role in
shifting the lasing wavelength. In a majority of circum-
stances, increasing solvent polarity will shift the gain
curve toward longer wavelength. In the case of more polar
dyes, the shift can be as high as 20 - 60 nm.
The output power of dye lasers is strongly dependent on
the purity of the solvent. Impurities and additives may
strongly affect upper state lifetime of the dye or may
catalyse photochemical reactions. Therefore, for best
results, only high quality solvents are to be recommended
[11].
With the exception of water, all solvents should be
considered hazardous. In many instances, the solvent in
which the dye is dissolved plays a major role in the hazard
presented by the final solution.
Water is called the universal solvent because more
substances dissolve in water than in any other chemical.
This has to do with the polarity of each water molecule.
The hydrogen side of each water (H2O) molecule carries a
slight positive electric charge, while the oxygen side car-
ries a slight negative electric charge. This helps water
dissociate ionic compounds into their positive and nega-
tive ions. The positive part of an ionic compound is at-
tracted to the oxygen side of water while the negative
portion of the compound is attracted to the hydrogen side
of water.
These hazards must be addressed carefully in dye han-
dling and solution preparation. Nearly all solvents are
highly flammable. Therefore, a small fire extinguisher
should be installed near the laser in a readily accessible
and unobstructed area.
A particular fire hazard that is not commonly known
occurs with nonpolar and, hence, nonconductive solvents.
If these solvents are circulated at a high speed through
plastic tubings, the pump unit acts as a van de Graff gen-
erator, producing up to 100 kV, and sparks may pierce the
tubing and ignite the solvent. The dye selectors use
grounding wires inside the plastic tubings to eliminate
these problems. However, when using such solvents,
check first for static electricity before opening the reser-
voir. Static electricity is present when hair on the back of
your hand or forearm is attracted to the plastic tubing. do
not circulate dye solutions made with such solvents for
more than a minute, unless the cuvette has been placed
into the crate and is grounded [12].
4. BEET ROOTS AND BEET DYES
The beet (Beta vulgaris) is a plant in the amaranth
family. It is best known in its numerous cultivated varie-
ties, the most well-known of which is probably the red
root vegetable known as the beetroot or garden beet.
However, other cultivated varieties include the leaf
vegetables chard and spinach beet, as well as the root
vegetables sugar beet, which is important in the produc-
tion of table sugar, and mangel-wurzel, which is a fodder
crop. Three subspecies are typically recognized. All cul-
tivated varieties fall into the subspeciesBeta vulgaris
subsp. vulgaris, while Beta vulgaris subsp. maritima,
commonly known as the sea beet, is the wild ancestor of
these and is found throughout the Mediterranean, the
Atlantic coast of Europe, the Near East, and India. A
second wild subspecies, Beta vulgaris subsp. adanensis ,
occurs from Greece to Syria.
Betacyanins (Bc) is extracted dyes from beetroot or
beet red (Beta vulgaris). The two hydro-soluble com-
pounds: betacyanin (Bc) and betaxanthins (Bx), which
present absorption bands at 540 and 480 nm, respectively
are obtained from aqueous extraction of beet red [13] as
seen in Figur e 1.
5. METHODOLOGY
5.1. Sample Preparation
The beet samples were collected from local markets in
Khartoum state and the dye solution was extracted by
water and the extracted was separated by filtration. Then
the ability of dyes solution to work as a laser gain medium
has been testified.
The dye solution was extracted by 0.1% aqueous TFA
(Tetra Fluoro Acetic acid).
Sample one: 1 ml of dye 0.1 solution was added to 100
ml of water (the absorbance of sample was adjusted to be
less than 0.1 au. Four different concentrations were pre-
pared by water dilution in the range of (0.1 - 0.01 au abs).
Sample two: 1 ml of dye solution was added to 100 ml
of glycerin-water (1:10) solution. Four different concen-
trations were prepared by dilution in the range of (0.1 -
0.01 au abs).
Sample three: 1 ml of dye solution was added to 100
ml of glycerin-water (2:10) solution. Four different con-
Figure 1. Structure of the main beetroot dyes. (A) betacyanins
(Bc) also known as betanin (with sugar moiety) and betanidine
without sugar and (B) betaxanthins (Bx).

A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188
1186
centrations were prepared by dilution in the range of (0.1 -
0.01 au abs).
Sample four: 1ml of dye solution was added to 100 ml
of glycerin-water (4:10) solution. Four different concen-
trations were prepared by dilution in range of (0.1 - 0.01
au abs).
5.2. Measurement Procedure
First step the absorbance at 538 nm for solution of
sample one was recorded, second one the fluorescence
spectrum of the same solution was recorded in 10 mm
fluorescence cuvette. Step 1 and 2 were repeated for four
solutions with increasing concentration of sample one.
Ostwald Device was used to determine the viscosities
of samples solvents.
Refractive indices and densities were determined by
using the mettler Toledo DR40 refractometer. Then the
fluorescence quantum yields of the solvents were deter-
mined by using the value of the refractive indexes which
given above.
6. RESULT AND DISSECTION
Table 2 shows relationship between the maximum
wavelength of light absorption (λmax) and beet dyes on
different pH was observed. The λmax of light absorption is
shifted as a result of the pH varying and the dye solution
showed instability at pH more than 8
Figure 2 showed four peaks and the HPLC fluores-
cence was running in 530 nm excitation wave length and
the emission wave length at 630 nm the result also showed
four strong peaks. One of the four components displayed
high emission peak this might mean that the dye solution
should have a significant fluorescence quantum yield.
Fluorescence of a molecule depends on the structure
and environment of the molecule such as interaction with
solvent and other dissolved compounds in the matrix, the
pH and concentration of the fluorescing species. Uncal-
Calib\beet root mix2 shown in Table 3.
The dye solutions of various concentrations were
pumped by a He-Ne flash lamp laser and the scatter light
was collected at 90˚ from the cuvette but unfortunately the
source of laser emission is weak at green area which is
absorbed by the dye solution, the results showed fluo-
rescence λmax that differ from fluorescence λmax of He-Ne
flash lamp laser (632.8 nm) that means the dye solution
should have a significant fluorescence quantum yield.
7. CALCULATION OF FLUORESCENCE
QUANTUM YIELD
To get fluorescence efficiency of various concentra-
tions of beet dyes a He-Ne flash lamp laser pumped them
to obtain fluorescence spectra peaks. Fluorescence spectra
peaks of various concentrations of beet dyes which are
pumped by a He-Ne flash lamp laser.
7.1. Density and Refractive Indices of
Solvents Samples Were Determined
as in Table 4
7.2. Fluorescence Quantum Yields
To calculate the fluorescence quantum yields for beet
dyes on different solvents, one can use the comparative
method by this equation;
Figure 2. HPLC-fluorescence for beet dyes solution.
Table 2. λmax depend on pH of solvent.
pH 3.15 4.07 5.15 6.30 7.19 8.24 9.03 10.15 11.00 12.00
λmax (nm) 485 485 475 475 480 ------ ------ 395 ------ ------
Table 3. Shows (Uncal-Calib\beet root mix2).
W05 [min] Height [%] Area [%] Height [mV] Area [mV.s] Reten. Time [min]
0.42 59.7 57.3 0.895 22.533 12.388 1
0.47 29.4 32.2 0.441 12.664 12.984 2
0.43 9.8 9.4 0.147 3.703 14.612 3
0.43 1.2 1 0.018 0.398 19.436 4
100 100 1.5 39.298 Total

A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188 1187
Ta b l e 4 . Densityand refractive indices of solvents of beet dyes
solutions.
Refractive indices
Density (g⁄cm3) at 23˚C No of sample
1.334 0.9979 1
1.342 1.0229 2
1.361 1.0563 3
1.380 1.0890 4
Grand
ФФ
Grand
XX
XST
ST ST








(7.1)
where, ФX, ФST, Ƞx, ȠST stand for fluorescence quantum
field of sample, fluorescence quantum field of standard,
refractive index of sample solventand refractive index of
standard solvent respectively. The value of ФX of four
samples were obtain, as shown in Table 5.
Calculation of the viscosity of solvents:
The calculation of the viscosity of solvents were shown
in Table 6.
The relationship between fluorescence quantum yield
and viscosity of solvent isrepresented as in the Figure 3.
The result gave a logarithmic function. The values of
Log Fluorescence quantum yieldand Log Viscosity of
solvent were presented in Table 7.
The relation of Log Fluorescence quantum yield and
Log Viscosity of solvent were presented in Figure 4.
The relationship between fluorescence quantum yield
(Ф) and the viscosity (λ) of the solvent has been derived
analytically and experimentally and is known as the
Forster-Hoffmann equation


log Фlo gCx

 where
C is a temperature-dependent constant and x is a dye-
dependent constant [14].
8. CONCLUSIONS
The fluorescence quantum yields of beet dyes solutions
were determined by the comparative method with rho-
damine b as standard. The fluorescence quantum yield
was developed by increasing the viscosity of solvents as
shown in Tables 6 and 7.
The result in Table 4 established that the beet dyes
solution has a high fluorescence quantum yield to act as a
laser gain medium.
Figure 2 shows four peaks, one of these components
displayed high emission, and this means that the dye
solution should have a significant fluorescence quantum
yield, which leads the solvent to act as gain medium.
The increasing of fluorescence quantum yield value as
a result of increasing the viscosity of solvent means that
the dye behaves like intramolecular charge transfer (ICT)
compounds because of the nitrogen atom attached the
-conjugation system [14].
Table 5. The values of fluorescence quantum yields for beet
dyes on different solvents.
No Sample
Gradx GradST ФST ȠST Ƞx Фx
1 313.5 899 0.31 1.3341.3440.114
2 483 899 0.31 1.3341.3420.169
3 577.7 899 0.31 1.3341.3610.200
4 874.2 899 0.31 1.3341.3800.323
Table 6. Viscosity values of solvents.
No Sample Solvent (ml:ml) Viscosity (cent-poise)
1 Water 0.9325
2 Water-glycerin (23:2) 2.1092
3 Water-glycerin (20:5) 3.7860
4 Water-glycerin (17:8) 7.6730
Table 7. Logarithmic data.
Log Fluorescence quantum yieldLog Viscosity of solvent
−0.943 −0.0303
−0.772 0.3228
−0.699 0.5782
−0.491 0.8900
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
02468
Fluorescence quantum yield
Viscosity (centi poise)
10
Figure 3. Relationship between fluorescence quantum yield and
viscosity of solvent.
-1
-0.8
-0.6
-0.4
-0.2
0
-0.200.2 0.4 0.6 0.81
log f q y
log viscosity
Figure 4. Function linearization.
On the basis of the results presented in this paper, it can
initially be concluded that lasing in beet dyes solution is

A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188
1188
possible. This is in agreement with the results of fluores-
cence quantum yield values of beet dyes solutions.
The measurements showed that the lasing wavelength
depends on the pH of the solvent and also the efficiency of
fluorescence depends on the viscosity of solvent.
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