Preparation And Luminescence Properties Of Rare Earth Doped Sodium Zinc Aluminum Phosphate Glass

White light emitting diode?WLED?is a new generation of lighting source with great potential,due to its tremendous merits such as compact size,high efficiency,long lifetime,energy saving and environmental protection.At present,phosphor-converted LEDs?pc-LEDs?,based on the combination of blue LED chips and YAG:Ce yellow phosphors,have become a mainstream product to achieve white light.However,there are some innate problems for the commercial dominant pc-LEDs,such as the deficiency of red emissive components and the poor thermal stability of the organic encapsulants,causing cool and not vivid light.To solve the problems,luminescent glass was prepared by a two-step method combining solution combustion method and melt-quenching method.Through different doping combination of Tm³⁺,Dy³⁺,and Eu³⁺,white luminescent glass with excellent luminescent perfomance is obtained.The experiments of solution combustion synthesis had shown that the glass phosphor could be obtained simply by grinding transparent glass.With urea as the fuel and the amount set to 1N?N is the theoretical amount?,glass was prepared under 400 ? for 30 min.During melt-quenching process,the melt was formed at 700 ? for 20 min using the glass phosphor as raw material.And then glass specimen could be obtained after the melt being cast,cooled,annealed cut and polished.As for the influences of oxides on the properties of phosphate glass,the result had shown that excess doping of rare ions leads to crystallization of glass.To make sure the product was homogeneous glass phase,the maximum doping amount of Tm³⁺,Dy³⁺,and Eu³⁺ were 3 mol%,4 mol%,and 2 mol%,respectively.Also,the content of Zn O had a certain influence on the formability and transmittance of the glass.The experimental result determined that the NZAP glass with composition of 15Na₂O-30 Zn O-5Al₂O₃-50P₂O₅ was optimal because of good formability and high transmittance for near violet and visible light.After being doped with rare earth ions,the glass had shown different luminescent properties.It could be found that the emission light is blue,yellow,and red using Tm³⁺,Dy³⁺,or Eu³⁺ as doping ion,respectively.And when the doping consentration of three ions was 2 mol%,3 mol% or 2 mol%,the intensity of respective emission reached the maximum.When Tm³⁺ and Dy³⁺ were co-doped,blue emission and yellow emission could both be found.Furthermore,the proportion of two emissions could be adjusted at different excitation wavelenths and via different doping concentration,thus the coordinates of eventrual emission could be varied in a large range.Via photoluminescence spectra and decay curves under defferent concentration of Dy³⁺,it could be demonstrated that there was energy transfer between Tm³⁺ and Dy³⁺ with high efficiency.and the transfer mechanism was electric dipole-dipole interaction.Moreover,after introducing Eu³⁺ to offset the red deficiency,the luminescent glass NZAP:Tm³⁺,Dy³⁺,Eu³⁺ emited warm white light with low correlated color temperature.With increasing temperature,on one hand,the chromaticity shift at 498 K was just 2.87×10^-2.On the other hand,the integrated emission intensity of the tri-doped glass decreased gradually,but the intensity at 498 K remained over 50% of that observed at 298 K.Therefore,the results indicated that the as-prepared co-doped glass had good thermal stability.