[Fabrication and Characterization of Planar Luminescent Solar Concentrator Waveguides Based on LR305 Dye].

Photovoltaic power generation is one of the best ways to utilize solar energy, but the cost of electricity is very high. To reduce the cost of photovoltaic power generation, in this paper, a type of planar luminescent solar concentrator waveguides based on Lumogen F Red 305 (LR305) dye with each size of 50 mm×50 mm×5 mm was proposed with radical polymerization method. The optical properties and photo-electricity outputs of the waveguides were characterized.

[Study on Fluorescence Properties of Flavanone and Its Hydroxyl Derivatives].

Flavanone derivatives are important active ingredients of natural medicine, so the synthesis of these compounds is one of the research hotspots of organic synthesis. Nevertheless, there is little research on fluorescence properties of these compounds up to now. Fluorescence properties of flavanone and 6 kinds of hydroxyl derivatives are studied in this paper. It is found that aqueous solutions of flavanone (FV), 7-hydroxyflavanone (7HF) and 6-hydroxyflavanone (6HF) have fluorescence, but aqueous solutions of 2'-hydroxyflavanone (2'HF), 4'-hydroxyflavanone (4'HF), naringenin and pinocembrin basically have no fluorescence. In three dimensional fluorescence spectra, excitation wavelengths λex of FV are located at 235, 265 and 340 nm, emission wavelength λem is at 386 nm; λex of 7HF are at 230, 276 and 315 nm, λem is at 391 nm; λex of 6HF are at 260 and 356 nm, em is at 482 nm. Influences of pH on fluorescence of FV, 7HF and 6HF are studied, and the reasons of pH affects on fluorescence are discussed from the viewpoint of molecular structure. The UV-absorption spectra of 7HF and 6HF at different pH are studied, and the proton ionization constants (pKa) of 7HF and 6HF are determined respectively to be 7.26±0.05 and 9.90±0.02, by a pH-absorption method. Influences of solvent (methanol) on fluorescence of FV, 7HF and 6HF are studied, and find that the fluorescence of FV and 7HF in methanol are weaker than that in water, but the fluorescence of 6HF in methanol is much stronger. In ordered media (SDS, CTAB and ß-CD), fluorescence of FV and 7HF decreased than that in water, but the fluorescence of 6HF enhanced in the media of ß-CD or CTAB. Using quinine sulfate or L-tryptophane as reference, fluorescence quantum yields of FV and 7HF aqueous solutions are measured to be 0.057 and 0.012, respectively; fluorescence quantum yields of 6HF in methanol or in aqueous solution containing 1.62 mg·mL-1 ß-CD are measured to be 0.064 or 0.012, respectively.

[Fluorescence enhancement of flavoxate hydrochloride in alkali solution and its application in pharmaceutical analysis].

Fluorescence enhancement reaction of flavoxate hydrochloride (FX) in strong alkali solution was studied, the mechanism of the reaction was investigated, and a novel fluorimetric method for analysis of FX in drug sample was established. FX has no intrinsic fluorescence, but it can slowly produce fluorescence in strong alkali solution. Heating can promote the fluorescence enhancement reaction. In 3D fluorescence spectra of the decomposition product of FX, two fluorescence peaks, located respectively at excitation wavelengths λex/ emission wavelength λem =223/410 nm, and 302/410 nm, were observed. Using quinine sulfate as a reference, fluorescence quantum yield of the decomposition product was measured to be 0.50. The structural characteriza- tion and spectral analysis of the decomposition product reveal that ester bond hydrolysis reaction of FX is firstly occurred during heating process, forming 3-methylflavone-8-carboxylic acid (MFA), then a cleavage reaction of the γ-pyrone ring of MFA occurred, producing α, ß-unsaturated ketone. This product includes adjacent hydroxyl benzoic acid group in its molecule, which can form intramolecular hydrogen bond under alkaline condition, so that increase the conjugate degree and enhance the rigidity of the molecule, and thereby cause fluorescence enhancement. Based on this fluorescence enhancement reaction, a fluorimetric method was proposed for the determination of FX. A linear calibration curve covered the concentration range 0.020 3-0.487 µg · mL. The regression equation was I(F) = 23.9 + 5357.3 c, with correlation coefficient r = 0.999 7 (n = 8), detection limit D = 1.1 ng · mL(-1). The method was applied to the analysis of FX tablets, with a spiked recovery rate of 100.2%. The reliability of the method was verified by a UV-spectrophotometric method.

[Fluorimetric analysis of camptothecin in Chinese herbal medicine common Camptotheca fruit].

Three-dimensional (3D) fluorescence spectra and thin layer fluorescence chromatogram of common Camptotheca fruit (CCF) crude drug, camptothecin (CPT) and 10-hydroxycamptothecin (HCPT) have been studied, and a novel fluorimetric method for determination of CPT in CCF crude drug has been established. In 3D fluorescence spectra, CPT presented 3 fluorescence peaks with excitation wavelengths lambdaex of 215, 255 and 365 nm, separately, and all peaks with emission wavelength lambdaem of 430 nm. HCPT presented 4 fluorescence peaks with lambdaex of 220, 265, 325 and 375 nm, separately, and all peaks with lambdaem of 555 nm. The fluorescence of CPT is much stronger than that of HCPT. Comparison of 3D fluorescence spectra and analysis of thin layer fluorescence chromatogram revealed that the main fluorescent component of CCF is CPT. HCPT and other components basically do not interfere with the fluorescence of CPT. Under the condition of pH 3.0-6.7, CCF aqueous solution can produce strong and steady fluorescence. Using methanol as solvent, the extracting solution of CCF was prepared, and diluted properly with water, then measured fluorescence intensity at lambdaex/lambdaem = 365/430 nm to determine the content of CPT. A linear calibration curve covered the concentration range 0.002 35-0.235 microg x mL(-1). The regression equation was IF = 9 + 30,844 c, with correlation coefficient r = 0.999 (n=9). The method has been applied to the analysis of CPT in a CCF sample, with a result of 0.127% and a spiked recovery rate of 102%. The reliability of the method has been verified by a thin layer chromatography-fluorescence scanning method. Experimental results demonstrated that this method can be used for quality evaluation of CCF crude drug.

[Synthesis and characterization of mixed metal oxide pigments].

In the present work, aluminum chloride and various soluble salts of doping ions were dissolved in water. In addition, urea and polyvinyl pyrrolidone (PVP) were also dissolved in the above aqueous solution under supersonic treatments. Then the solutions were heated to induce the hydrolysis of urea so that soluble aluminum and doping ions convert into insoluble hydroxide or carbonate gels. After calcinations, the obtained gels change to mixed metal oxide pigments whose color is related to type and concentrations of the doping ions. XRD characterization demonstrates that the diffraction patterns of the products are the same as that of alpha-alumina. Diffuse reflectance spectra of samples of the samples in UV-Vis regions show that the absorption bands for d-d transitions of the doping ions undergo considerable change as the coordinate environments change. In addition, L*, a* and b* values of the pigments were measured by using UV-Vis densitometer. SEM results indicate that the size of the pigment powders is in the range 200-300 nm. The pigments are quite stable since no evidence of dissolution was observed after the synthesized pigment is soaked for 24 hours. ICP test shows that very little amount of doped metal occurs in the corresponding filtrate. The above results suggest that these new kinds of mixed metal oxide pigments are stable, non-toxic, environmental friendly and they may be applicable in molten spinning process and provide a new chance for non-aqueous printing and dyeing industry.

[Synthesis and characterization of chromium doped Y3Al5O12 compound pigment].

The authors synthesized a new kind of green pigment via co-precipitation method by doping Y3Al5O12 with Cr+. The size of the pigment particles is around 200 nm as observed under scanning electron microscope. XRD results demonstrate that the pigment crystalline form of the pigment is yttrium alluminium garnet. UV-Vis spectra were used to investigate the coordination states and transition behavior of the doping ions. In addition, the colour feature was measured by CIE L* a* b* chroma value. The pigment was blended with polypropylene and then polypropylene fiber was produced using the polypropelene-pigment composite via molten spinning process. The distribution of the pigment particles in the polypropylene fibers was characterized by Xray computed tomography (CT) technique on the Beijing synchrotron radiation facility. The result states that the composite oxide pigment particles are homogeneously dispersed in the polypropylene fibers. The pigments are stable, non-toxic to the environment, and may be applied in non-aqueous dyeing to reduce waste water emitted by textile dyeing and printing industry.

[Fluorescence spectra and absorption spectra of carvacrol].

Fluorescence spectra and absorption spectra of carvacrol, an active component of Chinese herbal medicines, have been studied. The ionization constant and fluorescence quantum yield of carvacrol were measured according to spectral data. Under the condition of pH < 2.0, fluorescence intensity of carvacrol increases with the increase in pH value. In the range of pH 2.0-8.0, carvacrol gives a strong and steady fluorescence with maximum excitation wavelength 278 nm and emission wavelength 306 nm. When pH > 8.0, the fluorescence intensity decreases with the increase in pH value. Ionization constant of carvacrol was measured to be pK(a) = 10.44 +/- 0.06 using a pH-absorbance method; and pK(a) = 10.40 +/- 0.04 using a pH-fluorescence method. Fluorescence intensity of carvacrol was remarkably enhanced when methanol was added into its aqueous solution. Using L-tryptophane as a reference, the fluorescence quantum yield of carvacrol aqueous solution was measured to be 0.121 at excitation wavelength 278 nm; while in a solution containing 80% methanol, the quantum yield was measured to be 0.324.

[Using barium fluoride fine particles as stationary phase for TLC/FTIR analysis].

In situ TLC/FTIR technique has tremendous potential in the analysis of complex mixtures. However, the progress in this technique was quite slow. The reason is that conventional stationary phase such as silica gel etc. has strong absorption in FTIR spectrum and thus brings about severe interference in the detection of samples. To solve the problem, the authors propose to use barium fluoride fine particles as stationary phase of TLC plate. The reasons are as follows: Barium fluoride wafer has been extensively used as infrared window in FTIR experiments and it has no absorbance in an IR region between 4 000 and 800 cm'. As a matter of fact, the atomic mass of barium and fluoride is quite large, thus the normal vibration of BaF2 lattice is limited in far-IR region and low frequency part of mid-IR region. Therefore, the interference caused by IR absorption of stationary phase can be resolved if BaF2 is used as stationary phase of TLC plate. Moreover, BaF2 is quite stable and insolvable in water and most organic solvents and it will not be dissolved by mobile phase or react with samples in TLC separation. Additionally, decreasing the particle size of BaF2 is very important in TLC/FTIR analysis technique. The reason is two-fold: First, decreasing the particle size of stationary phase is helpful to improving the efficiency of separation by TLC plate; second, decreasing the size of BaFz particle can improve the quality of FTIR spectra by alleviating the problem of light scattering. By optimizing the synthetic conditions, fine particles of barium fluoride were obtained. SEM results indicate that the size of the BaF2 particles is around 500 nm. FTIR spectrum of the BaF2 particles shows that no absorption of impurity was observed. Moreover, the elevation of baseline caused by light scattering is insignificant. The authors have developed a new technique named "settlement volatilization method" to prepare TLC plate without polymeric adhesive that may bring about significant interference in FTIR analysis. Preliminary TLC experiments proved that the TLC plate using BaF2 fine particles as stationary phase can separate rhodamine B from methylene blue successfully. Applications of barium fluoride fine particles as stationary phase have bright perspective in the development of new in-situ TLC/FTIR analysis techniques.

[Preliminary investigation on the formation mechanism of CCL4-water-cetyl trimethyl ammonium bromide (CTAB) gel].

Gels are gaining extensive interest owing to their versatile applications in fields such as drug delivery, tissue engineering, cosmetics, templated materials and food industry. Surfactants have an ability to self-assemble into a variety of supramolecular aggregate structures and morphologies. Of particular interest in resent years are surfactant-based gels, one special class of materials due to surfactant assemblies resulting in viscoelastic solid-like rheological behaviors. Up to now, there is only limited understanding on the mechanism of gel formation, especially on the interaction among water, organic solvents and surfactant during thegel formation. In this study we prepare a Low-molecule-gel that is composed of cetyl trimethyl ammonium bromide (CTAB), water and carbon tetrachloride. Based on the experimental result of XRD and titration, the authors find that CTAB in gel are more than in saturated CTAB solution but CTAB is not solide in gel. CTAB is not solvented in CCl4. The solubility of CTAB in saturated CTAB solution is limited. So the authors suppose that CTAB is a synergistically solubilized by water and CCl4 in the gel. In addition, both NMR and FTIR spectroscopic results demonstrate that CTAB cations form a quasi-ordered structure in the gel.

A comparison of several second-order algorithms for simultaneous determination of neomangiferin and mangiferin with severe spectral overlapping in Anemarrhenae Rhizoma.

This work presents a greener approach for simultaneous determination of neomangiferin and mangiferin, the major bioactive constituents with severe spectral overlapping in Anemarrhenae Rhizoma, combining the sensitivity of molecular fluorescence and the selectivity of chemometric multivariate calibration algorithms. In this study, we compared the analytical performance of two group chemometric algorithms including trilinear algorithms such as parallel factor analysis (PARAFAC), alternating trilinear decomposition (ATLD), self-weighted alternating trilinear decomposition (SWATLD) and alternating penalized trilinear decomposition (APTLD), and PLS-based methods such as unfolded partial least-squares or the multi-dimensional partial least-squares, both combined with residual bilinearization (U-PLS/RBL, N-PLS/RBL). The statistical parameters for the validation set of the second calibration were evaluated through the relative error of prediction (REP%), the average recovery (Rec%), and the root mean square error of prediction (RMSEP). Prediction results for the validation set by trilinear algorithms showed that the values were satisfactory for neomangiferin, and higher and not acceptable values for mangiferin, while U-PLS and N-PLS predictions were very successful for two analytes. Therefore, U- and N-PLS/RBL were chosen to determine neomangiferin and mangiferin in more complex real samples simultaneously, and U-PLS/RBL algorithm showed the best performance. The predicted concentrations by proposed methods were satisfactorily compared with those obtained using high performance liquid chromatography with ultraviolet detection.

Time-resolved fluorescence and chemometrics-assisted excitation-emission fluorescence for qualitative and quantitative analysis of scopoletin and scopolin in Erycibe obtusifolia Benth.

This paper presents a new strategy for qualitative identification of scopoletin and scopolin in Erycibe obtusifolia Benth using time-resolved (lifetimes) fluorescence and quantitative analysis with chemometrics-assisted excitation-emission matrix (EEM) fluorescence. Due to the significant spectral overlapping among analytes and interference, the use of the more selective time-resolved fluorescence is proposed for qualitative identification in quality control of traditional Chinese medicine (TCM) for the first time. Using the strategy of combining EEM fluorescence with second-order calibration method, i.e. parallel factor analysis (PARAFAC), the simultaneous quantification of scopoletin and scopolin in the complex system of Erycibe obtusifolia Benth was achieved successfully. The predicted concentrations were compared with the values obtained using high performance liquid chromatography-coupled to fluorimetric detector (HPLC-FLD), and no significant differences between them were observed. Therefore, the proposed methods using time-resolved fluorescence for qualitative analysis and EEMs coupled with second-order calibration for quantitative analysis in TCM are comparable and provide a suitable alternative to the chromatography-based method.

[Fluorescence spectra and quantum yield of TiO2 nanocrystals synthesized by alcohothermal method].

Fluorescence spectra and fluorescence quantum yield of TiO2 nanocrystals were studied. Using tetra n-butyl titanate as a starting material, a facile alcohothermal technique was used to synthesize TiO2 nanocrystals. As can be seen from the transmittance electron microscopy (TEM) image, TiO2 nanocrystals with a relatively uniform particle size distribution of < 10 nm are present in the transparent sol. The transparent sol presents a strong stable fluorescence emission with a maximum at 450 nm, which is greatly dependent on the size quantization effects, defect energy level and the surface state of TiO2 nanocrystals. The quantum yield (gamma) of TiO2 was determined by the relative comparison procedure, using freshly prepared analytical purity quinine sulfate in 0.05 mol x L(-1) H2SO4 as a relative quantum yield standard. The emission quantum yield of TiO2 nanocrystals prepared in alcoholic media was calculated to be about 0.20 at wavelengths ranging from 330 to 370 nm, which was much higher than the values reported in previous works. So, it is supposed that nano-TiO2 will be applied as a potential quantum dots fluorescence probe in biological analysis.

Simultaneous determination of α-asarone and ß-asarone in Acorus tatarinowii using excitation-emission matrix fluorescence coupled with chemometrics methods.

A chemometrics-assisted excitation-emission matrix (EEM) fluorescence method was proposed for simultaneous determination of α-asarone and ß-asarone in Acorus tatarinowii. Using the strategy of combining EEM data with chemometrics methods, the simultaneous determination of α-asarone and ß-asarone in the complex Traditional Chinese medicine system was achieved successfully, even in the presence of unexpected interferents. The physical or chemical separation step was avoided due to the use of "mathematical separation". Six second-order calibration methods were used including parallel factor analysis (PARAFAC), alternating trilinear decomposition (ATLD), alternating penalty trilinear decomposition (APTLD), self-weighted alternating trilinear decomposition (SWATLD), the unfolded partial least-squares (U-PLS) and multidimensional partial least-squares (N-PLS) with residual bilinearization (RBL). In addition, HPLC method was developed to further validate the presented strategy. Consequently, for the validation samples, the analytical results obtained by six second-order calibration methods were almost accurate. But for the Acorus tatarinowii samples, the results indicated a slightly better predictive ability of N-PLS/RBL procedure over other methods.

[Fluorescence spectra of Bletilla striata aqueous extraction].

Three-dimensional fluorescence spectrum and ultraviolet absorption spectrum of Bletilla striata extraction drawn by boiling water were reported. Three fluorescence peaks, located at lambda(ex)/lambda(em) = 227/299 nm, 271/299 nm and 258/ 389 nm respectively, were observed in the three-dimensional fluorescence spectrum. Among them, the two former peaks having the same emission wavelengths were produced by one fluorescent component, while the latter peak was produced by another. Three-dimensional fluorescence spectrum is a characteristic mark of Bletilla striata, therefore it can be used in qualitative identification. The distance between emission wavelengths of the two components was 90 nm, so the fluorescence intensity of two components could be measured separately without pre-separation. For dilute solutions of Bletilla striata aqueous extraction, good linear relationships between fluorescence intensity and concentration of two components were obtained, thereby the quantitative determination of the two components may be carried out. In the range of pH 1.5 to pH 12.5, the fluorescence intensity of the two components changes with the increase in pH, indicating dissociable protons exist in the molecular structure of the two components.

[Fluorescence spectra of Dichroa febrifuga aqueous extraction].

Fluorescence spectra of chang shan (Dichroa febrifuga Lour) aqueous extraction were studied. In the three-dimensional fluorescence contour spectrum, three fluorescence peaks of quinazoline alkaloids, which are the active components of chang shan, were observed. The excitation wavelengths of the peaks were 235, 270 and 320 nm, respectively, and the emission wavelength of all the peaks was 430 nm. Three-dimensional fluorescence contour spectrum is the very image of fingerprint, suitable for qualitative identification of traditional Chinese medicine. In the range of pH 3 to pH 6, the fluorescence spectrum of chang shan aqueous extractions changes with the variation in pH value. The reason for this spectral change might be the protonation of N-1 in quinazolone ring of beta-dichroine (febrifugine) molecule. There is an excellent linear relationship between the fluorescence intensity and the concentration of chang shan under nearly neutral conditions, thereby a quantitative method for the determination of quinazoline alkaloids may be established.

[Fluorescence spectra and fluorescence quantum yield of triton X-100].

Fluorescence spectra and fluorescence quantum yield of triton X-100 (TX) aqueous solution are reported. In strong acidic solutions, TX gives no fluorescence. When pH > 1, TX gives a strong and steady fluorescence with the maximum excitation wavelengths at 229 and 275 nm, and the maximum emission wavelength at 302 nm, respectively. TX aqueous solution can produce resonance fluorescence. The resonance fluorescence peak is located at 285 nm. A linear relationship between the fluorescence intensity and TX concentration was found in the range of 0. 1-90 mg x L(-1). The detection limit of TX is 0.1 mg x L(-1). By using L-tryptophan as a reference, the fluorescence quantum yield of TX at maximum excitation wavelength 280 nm was measured to be 0.121.

[Ultraviolet absorption spectra of iodine, iodide ion and triiodide ion].

Ultraviolet absorption spectra of iodine I2, iodide ion I(-) and triiodide ion I3(-) were studied, and molar absorptivities of these species were determined. Absorption spectrum of I2 aqueous solution appears as an absorption peak at 203 nm with a molar absorptivity of 1.96 x 10(4) L x mol(-1) x cm(-1). Absorption spectrum of I(-) appears as two absorption peaks at 193 and 226 nm with molar absorptivities of 1.42 x 10(4) and 1.34 x 10(4) L x mol(-1) x cm(-1), respectively. When I2 aqueous solution is mixed with KI solution, two absorption peaks appear at 288 and 350 nm, respectively, indicating the formation of I3(-). Using saturation method, molar absorptivities of I3(-) at 288 and 350 nm were determined to be 3.52 x 10(4) and 2.32 x 10(4) L x mol(-1) x cm(-1), respectively.

[Resonance light scattering of 4-(2-pyridylazo)-resorcinol (PAR)].

Mechanism and influence factors of resonance light scattering (RLS) spectra of 4-(2-pyridylazo)-resorcinol (PAR) aqueous solution were studied. In weak acidic solutions, strong RLS of PAR can be observed. The spectral feature of RLS is related to the absorption spectra of PAR. Acidity of the solutions influenced the acid-base equilibrium of PAR and its existing state, thereby influenced the RLS intensity. At pH 3.1 to pH 6.2, PAR exists as neutral molecule, which may assemble into molecular aggregates by hydrophobic force giving a light scattering enhancement. By a light polarization experiment, the RLS of PAR was demonstrated to be complete polarized light. The relationship between RLS intensity and PAR concentration was examined to be linear at a given set of experimental conditions.

[Spectral properties, protonation and fluorescence quantum yield of ciprofloxacin].

Fluorescence spectra, ultraviolet absorption spectra, and protonation of Ciprofloxacin (CIP) at different pH values have been studied. Fluorescence quantum yield of CIP under neutral condition has been measured. In HCl medium with [H+] > 1 mol x L(-1), CIP molecules (simplified as HL) may accept three protons to exist as H4L3+ with very weak fluorescence, and its maximum fluorescence emission wavelength (lambdamax) is 456 nm. In acidic solution of pH 0 to pH 2, CIP mainly exists as H3L2+ form with lambdamax at 450 nm, and fluorescence intensity is relatively weak and increases with increasing of pH. In the range of pH 2 to pH 4, CIP mainly exists as H2L+ form with a strong fluorescence, and lambdamax is still at 450 nm. When pH>4, lambdamax gradually blue-shifts to 414 nm, fluorescence intensity slightly decreases as pH increases, and at the same time an evident change in ultraviolet absorption spectrum is observed, indicating that H2L+ has lost proton to exist as dipole ion form HL. When pH>8, the fluorescence intensity decreases until disappearance as pH increases, indicating that HL has lost proton to exist as non-fluorescence anion ion form L-. In the molecular form changing process, the maximum excitation wavelength of CIP is essentially constant at 275 nm, but the maximum emission wavelength changes obviously. In a buffer solution with pH 7.0, and using quinine bisulphate as a reference, the fluorescence quantum yield of CIP at maximum excitation wavelength 275 nm was measured to be 0.12.

[Fluorescence spectra and protonation of ofloxacin].

Fluorescence spectra, ultraviolet spectra and protonation of Ofloxacin (OFL) at different pH values have been studied. In strong acidic solutions, OFL molecule might accept two protons to exist as ternary acid H3L2+ with a maximum emission wavelength (lambdamax) at 505 nm. Along with the increase in pH value, fluorescence spectrum of OFL changed, an iso-fluorescence point at 352 nm was found in the fluorescence excitation spectra, and at the same time, isosbestic points were found in its UV absorption spectra. This spectral feature reveals that H3L2+ gradually lost hydrogen ion combined on C-4 keto oxygen. In the range of pH 2.5 to pH 4, OFL exists as H2L+ with lambdamax at 499 nm. When pH>4, the fluorescence emission peak at 499 nm gradually blue-shifted to 455 nm as pH was increasing, and an iso-fluorescence emission point was formed at 484 nm, indicating the dissociation of hydrogen ion of carboxylic acid at C-3. At about pH 7.0, OFL exists in the dipole ion form HL with lambdamax at 455 nm, which is the strongest fluorescence form. When pH>8, lambdamax red-shift from 455 to 475 nm as pH increases, meanwhile, fluorescence intensity decreases, indicating that HL lost hydrogen ion combined on N-4 of piperazinyl group. When pH>10, OFL exists in anion ion form L-, and fluorescence intensity decreases with pH increasing, but lambdamax remains essentially constant, indicating that medium environment influences the fluorescence property of OFL.