Near-infrared emitting Ca5 (PO4 )3 Cl:Eu2+ ,Nd3+ phosphor for modification of the solar spectrum.

Intense near-infrared (NIR) emitting phosphors Ca5 (PO4 )3 Cl:Eu2+ ,Nd3+ were synthesized using a conventional solid-state reaction method and characterized using X-ray diffraction, reflectance, photoluminescence (PL) emission and PL excitation (PLE) spectroscopy, and PL lifetime measurements. The emission could be excited by broad band radiation in the nUV region as a consequence of Eu2+ →Nd3+ energy transfer. The efficiency of Eu2+ →Nd3+ energy transfer was as high as 80.8%. Two components observed in the decay curves could be identified with Eu2+ substituting different Ca2+ sites. Eu2+ lifetimes were shortened after Nd3+ doping. Near infra-red emission intensity was limited by Nd3+ →Nd3+ energy transfer and the consequent concentration quenching. The critical distance for Nd3+ →Nd3+ energy transfer was estimated to be 11.41 Å. Absorption of nUV radiations followed by conversion to NIR indicated the potential application in solar photovoltaics.

Metal Quinolates as Phosphors for PC-LED Applications.

Metal quinolates, Liq Alq3 Znq2 Mgq2 exhibit efficient luminescence in blue green region and find applications as emission layer in OLEDs. In most of these quinolates the excitation spectra are broad in the range 350 to 410 nm, just short of emission spectra of efficient GaN based blue LEDs. In this paper we report metal quinolates synthesized by slightly modified method in which the excitation gets extended beyond 450 nm so that there is better overlap between emission spectra of blue LED and the excitation spectra. Therefore these phosphors may be used for PC-LED applications.

Synthesis and luminescence characterization of Y2 BaZnO5 :RE (RE = Eu3+ , Tb3+ , Pr3+ and Sm3+ ) phosphors.

Modified synthesis and luminescence of Y2 BaZnO5 phosphors activated with the rare earths (RE) Eu3+ , Tb3+ , Pr3+ and Sm3+ are reported. RE2 BaZnO5 phosphors have attracted attention because of their interesting magnetic and optical properties; and are usually prepared using a two-step solid-state reaction. In the first step, carbonates or similar precursors are thoroughly mixed and heated at 900°C to decompose them to oxides. To eliminate the unwanted phases like BaRE2 O4 , the resulting powders are reheated at 1100°C for a long time. We prepared Y2 BaZnO5 phosphors activated with various activators by replacing the first step with combustion synthesis. The photoluminescence results are presented. The photoluminescence results for Eu3+ , Tb3+ and Pr3+ are in good agreement with the literature. However, photoluminescence emission from Sm3+ has not been documented previously. The excitation spectrum of Eu3+ is dominated by a charge transfer band around 261 nm, and an additional band around 238 nm is always present, irrespective of the type of activator. The presence of this band for all these different types of activators was interpreted as host absorption.

Phosphor for phototherapy: Review on psoriasis.

We review developments in the field of phototherapy in terms of the treatment wavelength, dosimetry and phosphor used for different dermatoses. We attempt to categorize skin lesions and diseases by morphology, focusing on conditions that can be treated using phototherapy and photochemotherapy. Recent research and review articles are studied, the treatments explained and information on phototherapy that is applicable to psoriasis and other diseases is tabulated. The clinical features, epidemiology, epitalogy and various types of psoriasis, together with the therapies available to treat them are reported. Needs-based research has been carried out on narrow and broad band UVB wavelength-emitting phosphors and psoralen combined with UVA (PUVA) depending upon the disease undergoing treatment. Somewhat detailed descriptions of the different types of therapies used in the treatment of psoriasis are given. Phototherapy is shown to be a good therapeutic option for various types of skin diseases. The use of natural therapy has diminished as more people move towards artificial phototherapy like narrow band UVB, broad band UVB, PUVA and targeted phototherapy. The main advantages of these treatments are that they are safe and reduce erythema following treatment. Regarding safety issue the targated phototherapy pay more attention towards researcher.

Luminescence in Li2BaP2O7.

The photo-, thermo- and optically stimulated luminescence in Li2BaP2O7 activated with Eu(2+) /Cu(+) are reported. Strong thermoluminescence, which is about two times greater than LiF-TLD 100 was observed in the Eu(2+) -activated sample. It also exhibited optically stimulated luminescence sensitivity of ~20% that of commercial Al2O3:C phosphor.

Optically stimulated luminescence in LiCaAlF6:Eu2+ phosphor.

Results on optically stimulated luminescence (OSL) in LiCaAlF6:Eu(2+) are reported. Continuous wave OSL signal as recorded using blue (470 nm) stimulation was found to be ~31% that of standard phosphor lithium magnesium phosphate. The rate of OSL depletion for standard phosphor lithium magnesium phosphate is only three times less as compared with that of LiCaAlF6:Eu(2+). Strong photoluminescence (PL) in the near ultraviolet region is observed for LiCaAlF6:Eu(2+) with the characteristic Eu(2+) emission at 369 nm for 254 nm excitation. The thermoluminescence (TL) glow peak for LiCaAlF6:Eu(2+) was observed at around 180°C. The glow peak was about six times more intense compared with the dosimetric peak of the well known thermoluminescence dosimetric (TLD) phosphor LiF-TLD 100. Thus this phosphor deserves much more attention than it has received until now and may be useful as a dosimetric material in radiation dosimetry.

Luminescence and energy transfer in Ce3+, Mn2+- doped K2AEP2O7 (AE = Ca, Sr) phosphor.

Pyrophosphates K2AEP2O7 (AE = Ca, Sr) prepared by the classical solid-state technique and activated with Ce(3+) are described. Intense emission was observed in K2AEP2O7 (AE = Ca, Sr). The effect of Mn(2+) co-doping was studied. The broad emission peak of Mn(2+) was observed at 534 nm in K2 rP2O7:Ce(3+) and at 539 nm in K2CaP2O7:Ce(3+), Mn(2+). Mn(2+) emission was greatly enhanced by addition of the sensitizer Ce(3+) due to efficient energy transfer from Ce(3+) to Mn(2+).

Modification of luminescence spectra of CaF2:Eu2+.

CaF2:Eu(2+) is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid-state lighting (SSL), and down-conversion for solar cells. However, emission of CaF2:Eu(2+) is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue - 450 nm, green - 540 nm or red - 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF2:Eu(2+) to meet these requirements using co-dopants. A Ca0.49 Sr0.50 Eu0.01 F2 phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies.

Dy3+ and Mn2+ emission in fluoride- and chloride-based Na3 (SO4)X (X = F or Cl) phosphors.

In the present study, Na3 (SO4)X (X = F or Cl) halosulphate phosphors have been synthesized by the solid-state diffusion method. The phase formation of the compounds Na3 (SO4)F and Na3 (SO4)Cl were confirmed by X-ray powder diffraction (XRD) measurement. Photoluminescence (PL) excitation spectrum measurement of Na3 (SO4)F:Ce3+ and Na3 (SO4)Cl:Ce3+ shows this phosphor can be efficiently excited by near-ultraviolet (UV) light and presents a dominant luminescence band centred at 341 nm for Ce3+, which is responsible for energy transfer to Dy3+ and Mn2+ ions. The efficient Ce3+ → Dy3+ energy transfer in Na3 (SO4)F and Na3 (SO4)Cl under UV wavelength was observed due to 4 F(9/2) to 6H(15/2) and 6H(13/2) level, while Ce3+ → Mn2+ was observed due to (4) T1 state to (6) A1 . The purpose of the present study is to develop and understanding the photoluminescence properties of Ce3+ -, Dy3+ - and Mn2+ -doped fluoride and chloride Na3 (SO4)X (X = F or Cl) luminescent material, which can be the efficient phosphors in many applications, such as scintillation applications, TL dosimetry and the lamp industry, etc.

Wet-chemical preparation of Ce3+-activated K2LaX5 (X = Cl, Br or I) phosphors.

There has been a renewed interest in Ce(3+) -activated halide phosphors due to applications as scintillation detectors, especially for positron emission tomography. For K(2) LaCl(5), the light yield increases and the energy resolution (FWHM) improves with increasing Ce(3+) doping. K(2) LaX(5) compounds are also important as laser hosts for the mid-IR range. K(2) LaCl(5):Nd crystals show bright mid-IR luminescence, which makes them a candidate for IR laser materials. Efficient emission in the IR range has also been reported in K(2) LaCl(5):U(3+). A one-step, wet chemical process for preparing Ce(3+)-activated K(2) LaCl(5) phosphor is described. Intense luminescence of Ce(3+) can be observed in the as-prepared powders without any heat treatment. The availability of such powders opens up several exciting possibilities, such as growing single crystals without going to the high temperatures required for melting the constituent chlorides, or even obtaining processed, transparent, Ce(3+)-activated materials without taking recourse to crystal growth.

Luminescence studies of decomposition of ceric sulfate.

Literature results on the decomposition products of ceric sulfate are inconsistent. A group of researchers claim that ceric sulfate decomposed to ceric oxide without going through a cerous phase at any stage, while the results of the other group show that cerous sulfate is formed as an intermediate phase. Most of these studies used DTA/TGA, XRD and IR techniques. Cerous compounds can also be detected by the characteristic luminescence of Ce(3+). Using such techniques we show that the thermal decomposition of both monoclinic and ßCe(SO(4) )(2) · 4H(2) O in air at 500°C leads to the formation of cerous sulphate. Use of various atmospheres (air/N(2) /vacuum) and temperature profiles for the decomposition by the different researchers may be responsible for the discrepancies between literature results.

DEVELOPMENT OF NACL-BASED OPTICALLY STIMULATED LUMINESCENT PHOSPHORS FOR THE POSSIBLE APPLICATIONS IN DOSIMETRY.

New highly sensitive optically stimulated luminescent phosphors with NaCl moiety and dopants Ca,Cu,P/Mg,Cu,P are developed. These phosphors show very high optically stimulated luminescence (OSL) sensitivity. The dose response for NaCl:Ca,Cu,P is linear up to 1.2 Gy and for NaCl:Mg,Cu,P is slightly sub linear from 0.2 Gy. These phosphors show 30% fading during first 4 and later signal gets stabilised with no further signal loss. These sensitive phosphors will find applications in radiation dosimetry using OSL.

Local structure around Mn and Co in LaMn(1-x)Co(x)O(3 ± δ): an EXAFS study.

Detailed investigations of extended x-ray absorption fine structure (EXAFS) associated with the K-edges of Mn and Co have been carried out for LaMn(1-x)Co(x)O(3 ± δ) (0.3≤x≤1) compounds. It is found that the local structure around Mn is different from that around Co. The distortion in MnO(6) octahedra decreases with the increasing Co content whereas CoO(6) octahedra are undistorted over the entire range of x. The Co-O bond length has been found to decrease with the increase in x. Based on the information about the first shell, the structural anomalies observed in these compounds have been discussed. Complementary information obtained from the XRD and EXAFS studies have been used to explain the behaviour of resistivity in these compounds.

PHASE DEPENDENT OPTICALLY STIMULATED LUMINESCENCE IN CU-DOPED Sr4Si3O8Cl4.

Phase dependent optically stimulated luminescence (OSL) is studied in Cu-doped Sr4Si3O8Cl4. The Study shows that samples in which amount of contributing strontium metasilicate phase in Cu-doped Sr4Si3O8Cl4 is less, show intense OSL while those samples in which strontium metasilicate phase is more show weak OSL. The observed Cu luminescence is also found to be phase dependent. Sample in which Sr4Si3O8Cl4 phase is dominant, the observed Cu luminescence is around 350 nm whereas an additional longer wavelength band around 450 nm is observed when the strontium metasilicate phase is present in significant amount. The relatively phase pure, Cu-doped Sr4Si3O8Cl4 shows good OSL properties. The sensitivity of such material is 3.89 times more compared to commercial Al2O3:C (Landauer Inc.). High sensitivity, good linearity and reusability, along with low fading make this material as good OSL phosphor and may find applications in OSL based radiation dosimetry.

PHOTOLUMINESCENCE, THERMOLUMINESCENCE AND OPTICALLY STIMULATED LUMINESCENCE STUDIES IN ZINC-BASED FLUOROPERVOSKITES.

The optically stimulated luminescence, thermoluminescence and photoluminescence in various Cu and Ag doped zinc based fluoropervoskites are studied. In all the samples, photoluminescence of Cu+ and Ag+ is observed which could be attributed to 3d94 s1←→3d10 and 4d95 s1←→5d10 transitions, respectively. The observed emission is double humped and the main emission band shifts to the lower wavelength side with increasing ionic size of the alkali ion. All the studied fluoropervoskites show reasonable OSL sensitivity. Highest sensitivity is observed for Cu doped ZnNaF3 and is 25% compared to commercial Al2O3:C. Weak thermoluminescence is observed in all samples. In all Ag doped samples the TL peak is observed at 200°C whereas for Cu doped samples peak is observed at 150°C, and correlated with the OSL. The samples show good linear dose response in the 10 mGy-1.2 Gy range and show good reusability characteristics. This study will lead to the development of zinc-based fluoropervoskite phosphors for the radiation dosimetry using OSL.

Optically stimulated luminescence study in rare earth doped SrBPO5.

Optically stimulated luminescence (OSL) was studied in rare earth doped SrBPO5 for the possible applications in radiation dosimetry using optically stimulated luminescence. The study shows that the sensitivity of the Eu doped SrBPO5 shows good OSL and the sensitivity is comparable to that of Al2O3:C. It is observed that annealing has a profound effect on the OSL sensitivity. Slowly cooled Eu doped sample shows highest sensitivity and is 77% compared to that Al2O3:C whereas lowest sensitivity is observed in the quenched sample. Other properties like good linearity and low fading will make this phosphor suitable for the applications in radiation dosimetry using OSL.

Effect of Al(3+) co-doping on the luminescence properties of Cu doped Na2SiF6.

Studies were carried out to assess the correlation between thermoluminescence (TL) and optically stimulated luminescence (OSL) of this phosphor. It was observed that the OSL and TL glow curve consists of a wide distribution of traps having different photo-ionization cross-sections, trap depths and frequency factors. In case of Al doped sample, some of the traps up to 200°C are assumed to act as a source traps for the observance of OSL due to thermal transfer of charge carriers into the deep traps beyond 480°C. This suggests that Al impurities play an important role in the thermal transfer OSL process. As most of the work on this phenomenon is done on natural materials (mainly quartz) in which aluminum is a natural impurity, this study will explain the role of Al in this phenomenon.

Optically stimulated luminescence in doped NaF.

OSL in doped NaF is studied. Study shows that NaF:Mg,Cu,P phosphor possess good OSL properties having sensitivity comparable to that of commercially available Al2O3:C (Landauer Inc.). For the luminescence averaged over 3s the obtained OSL is 37% of that commercial available Al2O3:C. Of the several phosphors investigated, phosphor with impurities concentration Mg(0.01mol%), Cu(0.2mol%), P(1mol%) shows good OSL sensitivity good linearity in the 10mGy to 1Gy dose range and negligible fading. This sample shows a intense single TL peak around 350°C which gets depleted by 14% after the OSL readout. This imply that maximum OSL is coming from deep traps giving stability to the signal. The ease of preparation along with other good OSL properties will make this phosphor suitable for radiation dosimetry applications using OSL.

A new highly sensitive low-Z LiF-based OSL phosphor for radiation dosimetry.

A new low-Z lithium fluoride-based optical stimulated luminescent (OSL) phosphor is developed. The phosphor shows good OSL properties, and its sensitivity is comparable with that of the commercial Al2O3:C (Landauer, Inc.) phosphor. For the luminescence averaged over initial 3 s, blue stimulated luminescence (BSL) and green stimulated luminescence (GSL) sensitivities were found to be 0.27 and 4 times, respectively, than that of Al2O3:C (Landauer, Inc.). The BSL decay is fast, and the whole signal decays within 3 s; the GSL decay is relatively slow, and the signal decays in 25 s. The fast decay, good sensitivity, good linearity and its near tissue equivalence (Zeff ∼8.14) will make this phosphor suitable for radiation dosimetry particularly in personnel as well as in medical dosimetry.

Optically stimulated luminescence studies in combustion synthesized Al2O3:C,Cu,P.

A new Al2O3:C,Cu,P phosphor is developed by the combustion synthesis technique which exhibits entirely different OSL properties as compared to that of the commercial alumina. No thermoluminescence (TL) is observed in this phosphor which also differentiates the present phosphor from the commercially available Al2O3:C (Landauer). The phosphor shows good optically stimulated luminescence (OSL) sensitivity for ionizing radiation with a fast OSL decay as compared to the commercial Al2O3:C. The phosphor heated in air followed by heating under the reactive atmosphere exhibits maximum sensitivity amongst several other phosphors. On the basis of area integration method; integrated over initial 3s, the sensitivity of this phosphor is about 67% of that of commercial Al2O3:C.