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We report a change in the red photoluminescence of the Eu3+ doped Na 2 Sr 2 Al 2 PO 4 Cl 9 phosphor via doping of singly, doubly and triply ionized ions. The synthesized phosphors show good crystalline nature. The EDS analysis confirms the presence of desired elements in the phosphor samples. The vibrational feature of the phosphor was confirmed by FTIR analysis. The photoluminescence excitation spectra of the phosphor show three peaks at 317, 395 and 467 nm. The Eu3+ doped Na 2 Sr 2 Al 2 PO 4 Cl 9 phosphor emits intense red color on excitations with 395 and 467 nm wavelengths. However, the photoluminescence intensity of the phosphor is larger for 395 nm excitation. When the singly, doubly and triply ionized ions are co-doped in the Eu3+ doped Na 2 Sr 2 Al 2 PO 4 Cl 9 phosphor (i.e. F−, WO 4 2−, MoO 4 2−, VO 4 3−, La3+, and Y3+) the photoluminescence intensity of the phosphor is decreased significantly. The decrease in photoluminescence intensity is due to change in local crystal structure created by these ions. Interestingly, the photoluminescence intensity of phosphor increases many times when the (Y3+) ion incorporated phosphor is excited with 317 nm wavelength. The CIE diagram shows color emitted in the red region of visible spectrum and the color purity is larger for triply ionized (Y3+) ion. Thus, the singly, doubly and triply ionized ions activated Na 2 Sr 2 Al 2 PO 4 Cl 9 : Eu3+ phosphor may be used in displays devices, photonic devices, solid state lighting and white LEDs. Image 1 • A change in red photoluminescence was observed in the Eu3+ doped Na 2 Sr 2 Al 2 PO 4 Cl 9 phosphor via doping of ionised ions. • The phosphor emits intense red color on excitations with 317, 395 and 467 nm. • On doping of these ions, the PL intensity of the phosphor is decreased significantly. • The decrease in PL intensity is due to change in local crystal structure. • The PL intensity of phosphor enhances many times in the (Y3+) ion incorporated phosphor. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Sm3+ doped Y 2 O 3 phosphor was synthesized through solution combustion method. • The structural analysis shows an increase in the particles size of the phosphor. • The phosphor emits reddish orange color at 606 nm on excitation with 238, 363, 407, 424 and 464 nm wavelengths. • The emission intensity of the annealed phosphor is enhanced upto three times. • The lifetime of the 4G 5/2 level is increased in the annealed phosphor. Abstract This paper reports the downconversion photoluminescence in Sm3+ doped Y 2 O 3 nano-crystalline phosphor synthesized through solution combustion method. The structural characterization of the phosphor has been carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, which reveals its nano-crystalline nature. The particles size of the phosphor increases on annealing it, which has been confirmed by SEM measurement. The energy dispersive spectroscopic (EDS) measurement verifies the presence of Y, Sm and O elements in the phosphor. The Fourier transform infrared (FTIR) measurements show the presence of vibrational bands due to different groups in the phosphor. The photoluminescence excitation spectra of the phosphor show large number of excitation bands due to CTS and 4f-4f electronic transitions of Sm3+ ion. The Sm3+ doped Y 2 O 3 phosphor emits an intense reddish orange color centered at 606 nm due to 4G 5/2 → 6H 7/2 transition upon excitation with different wavelengths such as 238, 363, 407, 424 and 464 nm. The photoluminescence intensity is observed larger for 407 nm excitation. Interestingly, the peaks observed in the emission match well with those present in the excitation upon 238 and 363 nm excitations in lower wavelength side. The photoluminescence intensity of the phosphor sample is enhanced upto three times after annealing the as-synthesized phosphor. The improvement in the photoluminescence intensity is due to an increase in crystallinity, particles size and reduction in optical quenching centers. The lifetime of the 4G 5/2 level is found to be increased in the annealed phosphor. Thus, the Sm3+ doped Y 2 O 3 nano-crystalline phosphor may be a suitable candidate for displays and photonic devices. [ABSTRACT FROM AUTHOR]

Three photon upconversion photoluminescence has been observed in Tm 3+ , Yb 3+ co-doped ZnWO 4 phosphor synthesized through solid state reaction method. The structural measurements reveal an increase in crystallinity and particles size on Mg 2+ incorporation. The EDS spectrum shows the presence of Zn, W, Tm, Yb, Mg and O elements in the phosphor. The UV–vis-NIR absorption spectra contain CTB and 4f-4f transitions due to Tm 3+ and Yb 3+ ions, respectively. The Tm 3+ , Yb 3+ co-doped phosphor gives intense blue and NIR emissions alongwith a weak red emission due to 1 G 4 → 3 H 6 , 3 H 4 → 3 H 6 and 1 G 4 → 3 F 4 transitions, respectively upon 976 nm excitation. The emission intensity of the phosphor is found optimum at 2 mol% concentration of Yb 3+ ion. When the Mg 2+ ion is incorporated in the co-doped phosphor, the emission intensity enhances upto two times. This may be due to improved crystal structure and an increase in the intensity of absorption bands. The FIR analysis in the Stark components of 1 G 4 level suggests an efficient optical heating and temperature sensing ability. The temperature sensing sensitivity is found to be 34 × 10 −4 °K -1 at 300°K. Thus, the Tm 3+ , Yb 3+ , Mg 2+ tri-doped ZnWO 4 phosphor may be used in photonic devices, NIR source, as an optical heater and temperature sensor purposes. [ABSTRACT FROM AUTHOR]

The Tm 3+ , Yb 3+ co-doped gadolinium tungstate phosphor in presence and absence of alkali ions (i.e. Li + , Na + and K + ) has been synthesized through solid state reaction method. The structural characterization confirms the crystalline nature with coexistence of the two monoclinic phases. The phase fraction varies on addition of alkali ions. The Tm 3+ , Yb 3+ co-doped phosphor emits intense blue and near infrared emissions centered at 472 and 793 nm due to 1 G 4 → 3 H 6 and 1 G 4 → 3 H 5 transitions, respectively and a weak red emission at 655 nm due to 1 G 4 → 3 F 4 transition of Tm 3+ on excitation with 976 nm. The emission intensity of near infrared band dominates over the blue and red bands. When the alkali ions are added in the Tm 3+ , Yb 3+ co-doped phosphor, the emission intensity of the bands is enhanced significantly due to modification in the local crystal field. The emission intensity is highest for K + incorporation compared to Li + and Na + due to its occupancy at the interstitial sites. The lifetime measurement reveals an enhancement in the emission intensity. The pump power dependent emission intensity plots confirm the involvement of three photons for blue and two photons for red and NIR emissions. Thus, the Li + , Na + and K + incorporated Tm 3+ , Yb 3+ co-doped gadolinium tungstate phosphor emitting intense blue and NIR radiations may be useful for photonic devices, bio-imaging and solar converters. [ABSTRACT FROM AUTHOR]

This paper reports the frequency upconversion and downshifting emissions from Yb 3+ , Pr 3+ co-doped strontium aluminate nano-phosphor synthesized through solution combustion method. The structural measurements show nano-crystalline nature of the samples. The Fourier transform infrared measurements of the samples confirm the presence of different molecular species in the sample. The UV–vis–NIR spectrum of the sample shows absorption bands due to charge transfer band (CTB) and 4f–4f transition. The sample gives intense NIR upconversion emission centered at 854 nm on excitation with 976 nm laser. The emission intensity is optimum for 0.10 mol% concentration of Pr 3+ ion. The power dependent emission intensity measurement indicates the involvement of two photons for the upconverted emissions. The sample also emits intense blue upconversion and red downshifting emissions on excitation with 532 nm laser. The emission intensity of the bands is enhanced significantly on annealing the samples at higher temperature. The large enhancement in the emission intensity is a combined effect of rare earth concentration, crystallinity and reduction in optical quenching centers. Thus, the multi-modal Yb 3+ , Pr 3+ co-doped strontium aluminate nano-phosphor may be used for monochromatic source of NIR light, optical and display devices. [ABSTRACT FROM AUTHOR]

We report the structural and optical properties of Yb 3+ , Pr 3+ co-doped Y 2 O 3 nano-phosphor synthesized through solution combustion method. The structural studies reveal the nano-crystalline structure of the sample. The energy dispersive spectroscopy (EDS) measurements confirm the presence of Y, O, Pr and Yb elements in the sample. Fourier transform infrared studies show the vibrational features of the samples. The fluorescence spectra of the samples have been monitored on excitation with 976 nm and the intense green upconversion emission observed at 552 nm is due to 3 P 0 → 3 H 5 electronic transition. The concentration of Pr 3+ ion in the sample is optimized and the fluorescence intensity is maximum at 0.08 mol% of Pr 3+ . The power dependence studies reveal the involvement of two photons in the emission process. The possible mechanism of upconversion has been discussed on the basis of schematic energy level diagram. The sample annealed at higher temperature enhances the fluorescence intensity up to 8 times and this enhancement is discussed in terms of the removal of optical quenching centers. The nano-phosphor can be applicable in the field of display devices and green laser. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, Sm3+ doped La(OH)3 nano-phosphor (∼40nm) has been synthesized using combustion synthesis method and detailed structural and spectroscopic characterizations are carried out. On excitation with 532nm, several photoluminescence peaks extending over green to NIR regions have been observed and assigned to be due to 4f–4f transitions of Sm3+ ions. A bright orange-red perception is observed in annealed sample, which is 10 times higher than as synthesized sample. Time resolved emission spectroscopy reveals pronounced effect of heating, which induce good crystalline in the host. [Copyright &y& Elsevier]

• Eu3+ doped La 2 (MoO 4) 3 phosphor was prepared by solid state reaction method. • PLE spectra show an intense peak at 467 nm due to Eu3+ ion. • Eu3+ doped phosphor emits strong red emission upon 467 nm excitation. • Presence of PO 4 3-, SO 4 2- and VO 4 3- ions increase emission intensity of the phosphor. • This is due to an increase in local crystal structure and particles size. In this study, the Eu3+ doped La 2 (MoO 4) 3 phosphor has been successfully prepared by solid state reaction method. The prepared phosphors are crystalline and the particle size increases in the presence of phosphate, sulphate and vanadate ions. The photoluminescence excitation (PLE) spectrum of the Eu3+ doped La 2 (MoO 4) 3 phosphor shows an intense peak centered at 467 nm due to absorption by Eu3+ ions. On the excitation at 467 nm, the Eu3+ doped La 2 (MoO 4) 3 phosphor emits strong red emission centered at 614 nm, which is attributed to the 5D 0 → 7F 2 transition of Eu3+ ions. The emission intensity of the phosphors has been optimized by appropriate selection of the concentration of Eu3+ ions. When the phosphate, sulphate and vanadate ions are incorporated in the thermally stable Eu3+ doped La 2 (MoO 4) 3 phosphor the emission intensity of Eu3+ion is enhanced significantly. This occurs due to modification in the local crystal structure and the particle size increase. The CIE diagram shows the presence of emission bands in the visible spectrum. It also shows color tunability with a high color purity of the phosphor. The phosphate, sulphate and vanadate doped La 2 (MoO 4) 3 : Eu3+ phosphors may act as good candidates for the phosphor converted white LEDs in solid state lighting technology. [ABSTRACT FROM AUTHOR]

The Ca 2 Pb 3 (PO 4) 3 Cl: RE3+ (RE = Tb, Sm, Dy and Eu) phosphor materials were prepared by wet chemical method. The synthesized phosphors were analyzed by using XRD, SEM and photoluminescence (PL) characterization techniques. The excitation spectrum of the Ca 2 Pb 3 (PO 4) 3 Cl:Tb3+ phosphor consists of several bands in the 300–400 nm region by monitoring emission at 545 nm, which are assigned due to electronic transitions from 7F 6 to the upper levels of Tb3+ ion. The Ca 2 Pb 3 (PO 4) 3 Cl:Tb3+ phosphor emits efficient narrow green emission at 545 nm due to 5D 4 → 7F 5 transition upon 371 nm excitation. The PL excitation spectrum of the Ca 2 Pb 3 (PO 4) 3 Cl:Sm3+ phosphor exhibits narrow bands in the near ultraviolet (NUV) region due to Sm3+ ion. The Ca 2 Pb 3 (PO 4) 3 Cl: Sm3+ phosphor shows orange red emission centered at 598 nm, which is attributed to the 4G 5/2 → 6H 7/2 transition of Sm3+ ion. The concentration quenching has been studied in both the cases and the critical distance was calculated as 38.5 Å. The blue (482 nm) and yellow (576 nm) emissions are obtained in the Ca 2 Pb 3 (PO 4) 3 Cl:Dy3+ phosphor under 352 nm and 455 nm excitations, which are attributed to the 4F 9/2 → 6H 15/2 and 4F 9/2 → 6H 13/2 transitions of Dy3+ ion, respectively. However, the Ca 2 Pb 3 (PO 4) 3 Cl:Eu3+ phosphor emits strong orangish red emission centered at 594 nm, which is attributed to the 5D 0 → 7F 1 transition of Eu3+ ion on excitation with 396 nm. The CIE diagram shows green and orange red photoluminescence for the Ca 2 Pb 3 (PO 4) 3 Cl:Tb3+ and Ca 2 Pb 3 (PO 4) 3 Cl:Sm3+ phosphors, respectively whereas the bluish-yellow and orangish red photoluminescence for the Ca 2 Pb 3 (PO 4) 3 Cl:Dy3+ and Ca 2 Pb 3 (PO 4) 3 Cl:Eu3+ phosphors, respectively. The CIE coordinates indicate that the present phosphors have high color purity. These phosphors may act as good candidates for phosphor converted LEDs for solid state lighting technology. Image 1 • The Ca 2 Pb 3 (PO 4) 3 Cl: RE3+ (RE = Tb, Sm, Dy and Eu) phosphors were prepared by wet chemical method. • The Ca 2 Pb 3 (PO 4) 3 Cl: RE3+ (RE = Tb, Sm, Dy and Eu) phosphors emit multi-color photoluminescence upon suitable excitations. • The concentration quenching was explained by critical distance between the ions. • The CIE coordinates verify the presence of emitted colors in visible region. [ABSTRACT FROM AUTHOR]

The present study details the downshifting, frequency upconversion and intrinsic optical bistability in CaSc 2 O 4 :Ho3+/Yb3+ and upconversion in CaY 2 O 4 :Ho3+/Yb3+ phosphors synthesized by a complex-based precursor solution method. The X-ray powder diffraction confirms the formation of highly crystalline phosphors with pure orthorhombic phase. Fourier transform infrared studies of synthesized phosphors show vibrational bands due to the presence of Ca–O, Sc–O and Y–O groups. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to presence of Ho3+ and Yb3+ ions. The values of optical band gap (Eg) are found to be 5.69 eV and 5.58 eV for the Ho3+/Yb3+ codoped CaSc 2 O 4 and CaY 2 O 4 phosphors, respectively. The Ho3+/Yb3+ codoped CaSc 2 O 4 phosphors display intense green downshifting emission upon 454 nm excitations. The lifetime of green luminescence of CaSc 2 O 4 :Ho3+/Yb3+ phosphors with varied Yb3+ concentrations have also been measured. The decay curves show a non-exponential nature fitted to the Inokuti-Hirayama model and the energy transfer microscopic parameters have been also calculated. The Ho3+/Yb3+ co-doped CaSc 2 O 4 and CaY 2 O 4 phosphors display intense green alongwith weak blue, red, and near-infrared upconversion (UC) emissions upon 980 nm excitations. The spectral color purity (S gr) of CaSc 2 O 4 :Ho3+(1%)/Yb3+(5%) phosphor is calculated to be 0.78. Importantly, the variation of pump power generates intrinsic optical bistability (IOB) in the CaSc 2 O 4 :Ho3+(1%)/Yb3+(5%) phosphor for the green emission, which is not observed in the CaY 2 O 4 :Ho3+(1%)/Yb3+(5%) phosphor. Therefore, the Ho3+/Yb3+ co-doped CaSc 2 O 4 phosphor could potentially be used in UC-based devices, optical memory devices, optical gates, optical transistors and switching devices for optical communications. • The Ho3+/Yb3+ codoped CaSc 2 O 4 /CaY 2 O 4 phosphors were synthesized by complex based precursor solution method. • The Ho3+/Yb3+ codoped CaSc 2 O 4 phosphor displays intense green downshifting emission upon 454 nm excitation. • The Ho3+/Yb3+ co-doped CaSc 2 O 4 and CaY 2 O 4 phosphors produce intense green UC emission excited by 980 nm radiation. • The spectral color purity of (1%) Ho3+/(5%) Yb3+ codoped CaSc 2 O 4 phosphor is found to be 0.74. • The (1%) Ho3+/(5%) Yb3+ codoped CaSc 2 O 4 phosphor gives intrinsic optical bistability for the green emission. [ABSTRACT FROM AUTHOR]